Module 3: Toolbox of Individual Traffic Calming Measures Part 2

3.9 Roundabout

DESCRIPTION AND GENERAL PURPOSE

A roundabout is an intersection design that contrasts with designs that require traffic signal control or stop control. A roundabout is often used as a replacement for a signalized intersection. A small modern roundabout and mini-roundabout are similar (presented as a separate traffic calming measure in section 3.8 of this ePrimer [provide link]).

A full roundabout is typically appropriate only at the intersection of two arterial streets or of an arterial street with a collector street. The full roundabout does not generally fit within the footprint of lower classification street intersections.

A roundabout is sized to accommodate all large vehicles circulating the center island and the center island is non-traversable.

A roundabout provides a horizontal deflection with an island at the entry point and requires every vehicle to follow a circuitous path no matter which departure leg of the intersection is the destination (as illustrated in Figure 3.9.1). As a result, traffic speeds are moderated (note: even though overall delay per vehicle may be reduced in comparison to a signalized or stop-controlled intersection).

The roundabout is included as a traffic calming measure in this ePrimer because it can be used to change the operating character of a roadway as it transitions from a higher-speed operation to a lower-speed operation within a higher-density community with more pedestrian presence.

The reader is referred to NCHRP Report 672, Roundabouts: An Informational Guide for a thorough description of roundabout characteristics, applicability, effectiveness, and design issues.

just looked at it. looks like those links weren't on the legacy page (https://web.archive.org/web/20220707031920/https://safety.fhwa.dot.gov/hsip/legislation_guidance/). The page was edited on drupal and links added. But I can certainly migrate those pages.
Figure 3.9.1. Single-Lane Roundabout
(Source: Omni-Means, Ltd.)

APPROPRIATE APPLICATION

Appropriate Application – Roundabout
Type of Street	Appropriate for the junction of arterial streets and of arterial streets with collector streets¹⁰
Intersection or Roadway Segment	Applicable only at an intersection Can be used to realign a closely-spaced offset intersection into a single intersection; if intersection remains offset, roundabout can be laid out in the form of a "dogbone-shape" design
Roadway Cross-Section	Can be used at intersection of both one-way and two-way streets Approach legs can be multiple lanes Preferable to have an urban cross-section (i.e., curb and gutter) like that shown in Figure 3.9.2 Can be applied on a cross-section both with and without a bicycle facility; bicycle lane not striped within a roundabout Can be applied along a roadway with on-street parking
Speed Limit	Can accommodate any typical urban operating speed
Vehicle Traffic Volume	Can be appropriate at any level of traffic volume; multi-lane modern roundabout can be effective at daily entering volumes up to 60,000
Emergency Route	Can be appropriate along primary emergency vehicle route or street that provides access to a hospital or emergency medical services
Transit Route	Can be appropriate along a bus transit route
Access Route	Can be appropriate along a primary access route to commercial or industrial site
Grade	Can be installed on a crest vertical curve only if there is adequate stopping sight distance or warning signs are provided Maximum grade should comply with local standards and criteria; as an example, Portland OR limits longitudinal street grades at a roundabout to 10 percent

¹⁰ A mini-roundabout or traffic circle should be considered for the intersection of lower-classified roadways

Figure 3.9.2. Roundabout with Urban Cross-Section (i.e., Curb and Gutter)
(Source: James R. Barrera)

EFFECTS AND ISSUES

A complete description and discussion of the effects of a roundabout on mobility and safety is presented in NCHRP Report 672, Roundabouts: An Informational Guide.

ADDITIONAL DESIGN CONSIDERATIONS

A complete description and design considerations for a roundabout is presented in NCHRP Report 672, Roundabouts: An Informational Guide.

The MUTCD has sample striping layouts for single, multi-lane, and hybrid roundabouts.

3.10 Speed Hump

DESCRIPTION AND GENERAL PURPOSE

ITE has developed a recommended practice entitled Guidelines for the Design and Application of Speed Humps. Further guidance and clarification can be found in that publication.

A speed hump is an elongated mound in the roadway pavement surface extending across the travel way at a right angle to the traffic flow (see Figure 3.10.1). A speed hump is typically 3 inches in height (with applications as high as 4 inches) and 12 feet in length along the vehicle travel path axis (note: a speed hump that is 20 feet in length and flat in the middle is considered a speed table in this ePrimer).

At typical travel speeds along a residential street or in a small commercial business district, a speed hump produces sufficient discomfort to a motorist driving above the speed hump design speed to discourage speeding. It encourages the motorist to travel at a slow speed both upstream and downstream of as well as over the speed hump.

[A speed hump is also referred to as a road hump or undulation.]

[What's the difference between a speed hump and a speed bump? A speed hump is typically 12 feet in length (in the direction of travel), between 3 and 4 inches in height, and is intended for use on a public roadway. A speed bump is much shorter, between 1 and 2 feet in length (in the direction of travel). A speed bump can be as much as 6 inches in height. A speed bump is typically found in a parking lot or commercial driveway, but not on a public roadway.]

The initial speed hump applications were similar to the 12-foot speed hump, characterized in this section of the ePrimer. Variations in length and shape were applied and were initially considered speed hump variations. As the 20-foot measure became a standardized size and shape, it became known as a speed table. The reader is cautioned that when reviewing literature, design standards, and effectiveness analyses for speed hump, what is included within the umbrella of "speed humps" has varied over time.

[Five field studies of 51 speed humps measured crash reductions between 33 and 48 percent (Source: FHWA, Engineering Speed Management Countermeasures: A Desktop Reference of Potential Effectiveness in Reducing Crashes, July 2014) https://www.highways.dot.gov/safety/speed-management/engineering-speed-management-countermeasures-desktop-reference-potential]

[Seven field studies of 199 speed humps measured reductions between 6 and 13 mph for 85^th percentile speeds (Source: FHWA, Engineering Speed Management Countermeasures: A Desktop Reference of Potential Effectiveness in Reducing Speed, July 2014 https://www.highways.dot.gov/safety/speed-management/engineering-speed-management-countermeasures]

Figure 3.10.1. Speed Hump with Bicycle Lane and On-Street Parking
(Source: Scott Batson)

APPROPRIATE APPLICATION

Appropriate Application – Speed Hump
Type of Street	Appropriate for a residential local street or any street where the primary function is to provide access to abutting residential property (see Figure 3.10.2) Appropriate for a street that provides access to a school, park, or community center Also appropriate for neighborhood or residential collectors
Intersection or Roadway Segment	Placed at a midblock location, and not near an intersection; as an example, Pennsylvania recommends a distance of 150 feet from an unsignalized intersection and 250 feet from a signalized intersection Should not be placed on a sharp curve; ITE Guidelines for the Design and Application of Speed Humps recommends a minimum horizontal curve radius of 300 feet (see Figure 3.10.3)
Roadway Cross-Section	Can be used on a single-lane one-way street or two-lane two-way street; should stretch across only one travel lane in each direction Typically installed on a roadway with an urban cross-section (i.e., curb and gutter)¹¹ Typically placed one foot from a curb for drainage or six inches from the edge of a non-curbed roadway A speed hump can be applied on a cross-section both with and without sidewalks or bicycle facilities
Speed Limit	Appropriate if posted speed limit is 30 mph or less (per ITE Guidelines for the Design and Application of Speed Humps); many jurisdictions adhere to ITE maximum (e.g., South Carolina, Pennsylvania); some use a 25 mph ceiling (e.g., Delaware) Generally not appropriate when the pre-implementation 85th percentile speed is 45 mph or more
Vehicle Traffic Volume	Appropriate if daily traffic volume is relatively low; as examples, Pennsylvania sets a maximum daily volume of 3,500; South Carolina uses a maximum of 4,000; Pasadena, CA (41) uses a daily volume maximum of 4,000, with at least 1,000 vehicles in each direction ITE Guidelines for the Design and Application of Speed Humps recommends consideration only if no more than five percent of the overall traffic flow consists of long-wheelbase vehicles
Emergency Route	Generally not appropriate for a primary emergency vehicle route or a street that provides access to a hospital or emergency medical services; speed cushion and speed table are similar vertical measures that could be appropriate An emergency vehicle can cross a properly designed speed hump but at a slow speed
Transit Route	Generally not appropriate for a bus transit route but examples of speed humps on bus routes do exist; a speed table and speed cushion are similar vertical measures that could be appropriate
Access Route	Not appropriate along the primary access to a commercial or industrial site
Grade	Can be installed on, or beyond, a crest vertical curve only if there is adequate stopping sight distance or warning signs are provided ITE Guidelines for the Design and Application of Speed Humps recommends consideration only on a street with a grade of 8 percent or less (see Figure 3.10.4); many jurisdictions adhere to that maximum (e.g. Pennsylvania, South Carolina) but others follow a lower value: Delaware – 6 percent; Minnesota and Pasadena, CA -5 percent

¹¹ If the street does not have curbing, an obstruction such as signing, flexible delineator posts, or bollards may be necessary to discourage a motorist from driving around the hump. Potentially hazardous objects (e.g., rocks, boulders) should not be used.

Figure 3.10.2. Speed Hump on Residential Neighborhood Street
(Source: Lucy Gibson)

"Figure 3.10.3. Speed Hump Along Horizontal Curve. This figure contains a photograph of a curving two lane road divided by a double yellow line in a wooded area. Just before the curve a speed hump is in place a short distance from a cross walk. The crosswalk is indicated by green diamond signs on the right hand side of the road."
Figure 3.10.3. Speed Hump Along Horizontal Curve
(Source: Scott Wainwright)

"Figure 3.10.4. Speed Hump on a Grade. This figure contains a photograph looking down a hill. The two lane, unmarked road, has an oncoming car in the left lane just about to cross over a speed hump."
Figure 3.10.4. Speed Hump on a Grade
(Source: Scott Wainwright)

EFFECTS AND ISSUES

Effects and Issues – Speed Hump
Vehicle Speed	Single speed hump reduces vehicle speeds to the range of 15 to 20 mph when crossing the hump; speed reduction effects decline at the rate of approximately 0.5 to 1 mph every 100 feet beyond the 200 foot approach and exit of a speed hump; in order to retain slower vehicle speeds over longer distance, series of speed humps is needed (see Figure 3.10.5) ITE Guidelines for the Design and Application of Speed Humps recommends spacing of 260' to 500' to keep 85th percentile operating speed between 25 and 30 mph; some jurisdictions have refined guidelines: Pennsylvania – spacing between 250 and 600 feet South Carolina – spacing of no less than 350 feet Virginia – spacing of approximately 500 feet, clear visibility of 200 feet, and placement no closer than 200 feet from an intersection Pasadena – speed hump series only on street segment that is at least 1,200 feet in length and traffic signals or Stop signs are at least 1,200 feet apart Proper placement of initial speed hump in a series is significant; ITE Guidelines for the Design and Application of Speed Humps recommends that the first speed hump in a series be normally located in a position where it cannot be approached at high speed from either direction; to achieve this objective, it is typically installed within 200 feet or less of a small-radius curve or Stop sign or, if installed on a street with a significant downgrade, at the top of a hill Refer to Module 4 for additional data
Vehicle Volume	As single installation, there is little traffic diversion from the street; as part of a series, typical volume reductions of 20 percent observed Refer to Module 4 for additional data
Pedestrian Safety and Mobility	Not a preferred location for a crosswalk Refer to Module 6 for additional discussion
Bicyclist Safety and Mobility	Bicyclist safety should not be affected; some jurisdictions use maximum street grade of 5 percent on a street with a speed hump if designated as a bicycle route Bicyclist can negotiate speed hump with little delay or discomfort; it is also possible for a bicyclist to bypass a speed hump by passing through the gap between the hump and the curb and gutter Refer to Module 6 for additional discussion
Motorist Safety and Mobility	Speed effects of a single or series of speed humps are greater than for any other traffic calming measure with the exception of route diversions that eliminate a particular traffic movement Produces sufficient discomfort to a motorist driving above the speed hump design speed to discourage speeding
Emergency Vehicle Safety and Mobility	Typical delay for a fire truck is in the 3 to 5 second range; for an ambulance with a patient, delay can be as much as 10 seconds Refer to Module 5 for additional discussion
Large Vehicle Safety and Mobility	Typical delay for a large commercial vehicle is in the 3 to 7 second range Refer to Module 5 for additional discussion
Accessibility of Adjacent Property	Does not typically require removal of any on-street parking or affect accessibility of adjacent property (see Figure 3.10.6)
Environment	Potential for increased noise due to vehicle braking and accelerating and to the vibration of loose items in truck beds or trailers
Design Issues	Placement factors include vertical and horizontal alignment of the street, proximity to the nearest intersection, location of driveways and on-street parking, presence or absence of street lighting, location of designated pedestrian crossings, drainage, and utility access points (drains, valves, etc.) Should not require relocation of above- and below-ground utilities May not be appropriate on a roadway where drainage gutter or flow of water is in the center of the roadway; drainage and hydraulic impacts need careful evaluation

"Figure 3.10.5. Series of Speed Humps. This figure contains a photograph of an undivided street in a tree-lined residential area. A sign post with a yellow diamond speed hump sign and a rectangular 15 MPH speed limit sign is on the right hand side of the street. A series of speed humps is visible as the street vanishes into the distance."
Figure 3.10.5. Series of Speed Humps
(Source: City of Stockton, California)

"Figure 3.10.6. On-Street Parking Adjacent to Speed Hump. This figure contains a photograph of a curved street in a residential area. A car is parked near the curb beside a signpost with a yellow diamond speed hump sign and a 15 MPH speed limit sign. Other cars can be seen parked on either side of the street."
Figure 3.10.6 Adjacent to Speed Hump
(Source: Lewis Grimm)

ADDITIONAL DESIGN CONSIDERATIONS

ITE provides specific design and application guidance for speed humps; refer to Guidelines for the Design and Application of Speed Humps.

ITE guidelines specify a speed hump that is 12 feet long (in the direction of travel) and 3 inches in height.

A sample design for a speed hump is presented in Figure 3.10.7.

Figure 3.10.7. Sample Design for Speed Hump
(Source: Delaware Department of Transportation)

3.11 Speed Cushion

DESCRIPTION AND GENERAL PURPOSE

A speed cushion consists of two or more raised areas placed laterally across a roadway (see Figure 3.11.1). The height and length of the raised areas are comparable to the dimensions of a speed hump. The primary difference is that a speed cushion has gaps (often referred to as "cutouts") between the raised areas to enable a vehicle with a wide track (e.g., a large emergency vehicle, some trucks, some buses) to pass though the feature without any vertical deflection.

Another difference between a speed cushion and a speed hump is the common practice for the top of the speed cushion to be level. Like a speed hump, the profile of a speed cushion is gentle enough to provide a comfortable ride when traversed at a speed of approximately 20 to 25 MPH.

[A speed cushion is also known as a speed lump, speed slot, and speed pillow.]

The cutouts in the speed cushions are positioned such that a passenger vehicle cannot pass it without traveling over a portion of the raised pavement.

A speed cushion is often a preferred alternative to a speed hump on a primary emergency response route or on a transit route with frequent service.

[Two field studies of three speed cushions measured reductions between 5 and 7 mph for 85^th percentile speeds (Source: FHWA, Engineering Speed Management Countermeasures: A Desktop Reference of Potential Effectiveness in Reducing Speed, July 2014) https://www.highways.dot.gov/safety/speed-management/engineering-speed-management-countermeasures]

Figure 3.11.1. Speed Cushion with Passage that Straddles Centerline
(Source: Jeff Gulden)

APPROPRIATE APPLICATION

Appropriate Application – Speed Cushion
Type of Street	Generally appropriate for both local and collector streets
Intersection or Roadway Segment	Placed at a midblock location; as an example, Pennsylvania recommends a distance of 150 feet from an unsignalized intersection and 250 feet from a signalized intersection Should not be placed on a sharp curve; ITE Guidelines for the Design and Application of Speed Humps recommends a minimum horizontal curve radius of 300 feet
Roadway Cross-Section	Can be used on a single-lane one-way or two-lane two-way street (examples are shown in Figures 3.11.2 and 3.11.3) Typically installed with an urban cross-section (i.e., curb and gutter)¹² Can be applied on a cross-section both with and without sidewalks or bicycle facilities
Speed Limit	Appropriate maximum speed limit is 30 mph or less (per ITE Guidelines for the Design and Application of Speed Humps); many jurisdictions follow the same maximum speed limit (e.g., South Carolina, Pennsylvania); others have chosen a 25 mph maximum (e.g., Delaware, Pasadena)
Vehicle Traffic Volume	Appropriate measure if the daily traffic volume is relatively low; a variety of maximum volumes are in use for speed humps; as examples, Pennsylvania sets a maximum daily volume of 3,500; South Carolina uses a maximum of 4,000; on a local level, Pasadena, CA uses a daily volume maximum of 4,000, with at least 1,000 vehicles in each direction ITE Guidelines for the Design and Application of Speed Humps recommends consideration only if no more than five percent of the overall traffic flow consists of long-wheelbase vehicles
Emergency Route	Appropriate for a primary emergency vehicle route and on a street that provides access to a hospital or emergency medical services An emergency vehicle can cross a properly designed speed cushion at a speed near the speed limit
Transit Route	Appropriate for a bus transit route
Access Route	Appropriate along the primary access to a commercial or industrial site
Grade	Can be installed on a crest vertical curve only if there is adequate stopping sight distance or warning signs are provided IT E Guidelines for the Design and Application of Speed Humps recommends consideration only on a street with a grade of 8 percent or less; many jurisdictions adhere to that maximum (e.g. Pennsylvania, South Carolina) but others follow a lower value: Delaware – 6 percent; Minnesota and Pasadena, CA – 5 percent

¹² If the street does not have curbing, an obstruction such as signing, flexible delineator posts, or bollards may be acceptable to prevent a motorist from driving around the cushion. Potentially hazardous objects (e.g., rocks, boulders) should not be used.

"Figure 3.11.2. Speed Cushion with Median. Please see the Extended Text Description below."
Figure 3.11.2. Speed Cushion with Median
(Source: Scott Wainwright)

Figure 3.11.2. Speed Cushion with Median. Please see the Extended Text Description below.
Figure 3.11.3. Speed Cushion with Continuous Two-Way Left-Turn Lane
(Source: www.pedbikeimages.org / Michael Cynecki)

EFFECTS AND ISSUES

Effects and Issues – Speed Cushion
Vehicle Speed	Single speed cushion reduces vehicle speeds to the range of 15 to 20 mph when crossing the cushion; speed reduction effects decline at the rate of approximately 0.5 to 1 mph every 100 feet beyond the 200 foot approach and exit of a speed cushion; in order to retain slower vehicle speeds over longer distance, a series of speed cushions needed Average speeds are typically higher than for a speed hump because speed cushion allows a motorist to pass over the cushion with one wheel on the cushion and one wheel off ITE Guidelines for the Design and Application of Speed Humps recommends spacing of 260' to 500' to keep 85th percentile operating speed between 25 and 30 mph; some jurisdictions have refined guidelines: Pennsylvania – spacing between 250 and 600 feet South Carolina – spacing of no less than 350 feet Virginia – spacing of approximately 500 feet, clear visibility of 200 feet, and placement no closer than 200 feet from an intersection Pasadena – speed cushion series only on street segment that is at least 1,200 feet in length and traffic signals or Stop signs are at least 1,200 feet apart Proper placement of initial speed cushion in a series is significant; ITE "Guidelines for the Design and Application of Speed Humps" recommends "the first speed [cushion] in a series is normally located in a position where it cannot be approached at high speed from either direction; to achieve this objective, it is typically installed within 200 feet or less of a small-radius curve or Stop sign or, if installed on a street with a significant downgrade, at the top of a hill" Refer to Module 4 for additional data
Vehicle Volume	As single installation, there is little traffic diversion from the street; as part of a series, typical volume reductions of 20 percent observed Refer to Module 4 for additional data
Pedestrian Safety and Mobility	Not a preferred location for a crosswalk Refer to Module 6 for additional discussion
Bicyclist Safety and Mobility	Bicyclist safety and mobility not affected; bicyclist can pass through the speed cushion gaps Refer to Module 6 for additional discussion
Motorist Safety and Mobility	Speed effects of a single or series of speed cushions are greater than for any other traffic calming measure with the exception of route diversions that eliminate a particular traffic movement Produces sufficient discomfort to a motorist driving above the speed cushion design speed to discourage speeding In the UK, where speed cushions are more common than they are currently in the United States, a field study found that 45 percent of passenger car motorists aimed for the gaps when traversing a speed cushion (i.e., one wheel on the hump and one wheel on the flat pavement); this is a safety concern when the speed cushion gaps coincide with the street centerline A motorcycle can pass through a speed cushion gap without slowing
Emergency Vehicle Safety and Mobility	Speed reduction for emergency vehicles is minimal because the larger vehicles can straddle the cushions (see Figure 3.11.4); if the emergency vehicle has the track width of a passenger car (e.g., an ambulance), there is delay Offset speed table is a comparable vertical measure designed to accommodate emergency vehicle mobility Refer to Module 5 for additional discussion
Large Vehicle Safety and Mobility	Speed reduction for large commercial vehicles is minimal because the larger vehicles can straddle the cushions Refer to Module 5 for additional discussion
Accessibility of Adjacent Property	On-street parking does not need to be removed and there is no reduction in accessibility of adjacent property
Environment	Potential for increased noise due to vehicle braking and accelerating and to the vibration of loose items in truck beds or trailers
Design Issues	Placement factors include vertical and horizontal alignment of the street, proximity to the nearest intersection, location of driveways and on-street parking, presence or absence of street lighting, location of designated pedestrian crossings, drainage, and utility access points (drains, valves, etc.) Should not require relocation of above- and below-ground utilities

Figure 3.11.4. Fire Truck Approaching Test Speed Cushion
(Source: Jeff Gulden)

ADDITIONAL DESIGN CONSIDERATIONS

Pavement markings (e.g., striping, arrows) and signage for a speed cushion should replicate those for a speed hump.

A speed cushion is typically designed with sides that taper off at the gutter for drainage. This design may be modified to end the taper further from the gutter to create a wide, flat surface for a bicycle bypass lane, if desired.

An issue that has generated discussion regarding speed cushion applications is the appropriate cushion width. It is common for heavier vehicles like transit buses and fire trucks to use dual rear wheels. These result in the clear space between the wheels of large vehicles to more closely match the track width of a larger sedan or SUV. The cushion width should be wide enough to slow personal passenger vehicles and yet narrow enough to permit fire trucks and transit vehicles to pass easily, without overloading the rear axles of those heavier vehicles.

Sample designs for speed cushions without and with a median are presented in Figures 3.11.5 and 3.11.6, respectively.

Figure 3.11.5. Sample Design for Speed Cushion without a Median
(Source: Delaware Department of Transportation)

Figure 3.11.6. Sample Design for Speed Cushion with a Median
(Source: Delaware Department of Transportation)

3.12 Speed Table

DESCRIPTION AND GENERAL PURPOSE

A speed table is a raised area placed across the roadway designed to physically limit the speed at which a vehicle can traverse it. Like a speed hump, it extends across the travelway. Unlike a speed hump, a speed table has a long enough flat top (typically, 10 feet) to accommodate the entire wheelbase of most passenger cars. The longer longitudinal depth in the direction of travel enables comfortable and safe vehicle operating speeds that are faster than for a speed hump. Figure 3.12.1 illustrates a typical application.

When a speed table is designated as a crosswalk through the use of striping, it is known as a raised crosswalk (see section 3.14).

[Three field studies of 27 speed tables measured crash reductions between 36 and 64 percent (Source: FHWA, Engineering Speed Management Countermeasures: A Desktop Reference of Potential Effectiveness in Reducing Crashes, July 2014) https://www.highways.dot.gov/safety/speed-management/engineering-speed-management-countermeasures-desktop-reference-potential]

[Six field studies of 98 speed tables measured reductions between 4 and 11 mph for 85th percentile speeds (Source: FHWA, Engineering Speed Management Countermeasures: A Desktop Reference of Potential Effectiveness in Reducing Speed, July 2014) https://www.highways.dot.gov/safety/speed-management/engineering-speed-management-countermeasures]

Figure 3.12.1. Typical Speed Table Application
(Source: www.pedbikeimages.org / Austin Brown)

APPROPRIATE APPLICATION

Appropriate Application – Speed Table
Type of Street	Can be installed on a local street, collector street, and in certain circumstances, an arterial street
Intersection or Roadway Segment	Placed at a midblock location; Pennsylvania recommends a distance of 150 feet from an unsignalized intersection and 250 from a signalized intersection If placed at an intersection, called a raised crosswalk or raised intersection Should not be placed on a sharp curve; ITE Guidelines for the Design and Application of Speed Humps recommends a minimum horizontal curve radius of 300 feet
Roadway Cross-Section	Can be used on a single-lane one-way or two-lane two-way street (see Figure 3.12.2) Typically installed with an urban cross-section (i.e., curb and gutter)¹³ but an open section can be acceptable Can be applied both with and without sidewalks or bicycle facilities
Speed Limit	ITE Guidelines for the Design and Application of Speed Humps recommends consideration only on a street with a posted speed limit of 30 mph or less; many jurisdictions follow the same maximum (e.g., South Carolina, Pennsylvania); others have chosen a 35 mph maximum (e.g., Delaware, Pasadena) Generally not appropriate when the pre-implementation 85th percentile speed is 45 mph or more
Vehicle Traffic Volume	Some jurisdictions provide guidance on a maximum traffic volume that can be properly accommodated; Pennsylvania sets a maximum daily volume of 3,500; South Carolina uses a maximum of 4,000; Pasadena, CA uses a maximum of 4,000, with at least 1,000 vehicles in each direction ITE Guidelines for the Design and Application of Speed Humps recommends consideration if no more than five percent of the overall traffic flow consists of long-wheelbase vehicles
Emergency Route	Generally not appropriate for a primary emergency vehicle route or street that provides access to a hospital or emergency medical services; another form of vertical deflection – a speed cushion -could be appropriate
Transit Route	Generally not appropriate for a bus transit route with BRT, Express, or Limited Stop service (unless the posted speed limit is 30 mph or less); speed cushion could be appropriate Can be appropriate along a neighborhood circulator or other local bus service route Should not be located near bus stop to insure passengers are not transitioning between standing and sitting as the bus crosses over the speed table
Access Route	Not appropriate along the primary access to a commercial or industrial site
Grade	Can be installed on, or beyond, a crest vertical curve only if there is adequate stopping sight distance or warning signs are provided ITE Guidelines for the Design and Application of Speed Humps recommends consideration only with a grade of 8 percent or less; many jurisdictions adhere to that maximum grade (e.g. Pennsylvania, South Carolina) but others follow a lower maximum: Delaware – 6 percent; Minnesota – 5 percent

¹³ If the street does not have curbing, an obstruction such as signing, flexible delineator posts, or bollards may be acceptable to prevent a motorist from driving around the table. Potentially hazardous objects (e.g., rocks, boulders) should not be used.

Figure 3.12.2. Speed Table with Choker
(Source: Google Street View)

EFFECTS AND ISSUES

Effects and Issues – Speed Table
Vehicle Speed	Single speed table reduces 85^th percentile speeds to the range of 25 to 35 mph when crossing the table; speed reduction effects decline at the rate of approximately 0.5 to 1 mph every 100 feet beyond the 200 foot approach and exit of a speed table; in order to retain slower vehicle speeds over a longer distance, a series of speed tables is needed (as shown in Figure 3.12.3) ITE Guidelines for the Design and Application of Speed Humps recommends a spacing of between 260 and 500 feet; some jurisdictions have refined these guidelines: Pennsylvania – spacing between 250 and 600 feet South Carolina – spacing of no less than 350 feet Virginia – spacing of approximately 500 feet, with clear visibility of 200 feet, and placement no closer than 200 feet from an intersection Pasadena – only on a street segment that is at least 1,200 feet in length and on which any traffic signals or Stop signs are at least 1,200 feet apart Proper placement of the initial speed table in a series is significant; ITE Guidelines for the Design and Application of Speed Humps recommends "the first speed [table] in a series is normally located in a position where it cannot be approached at high speed from either direction; to achieve this objective, it is typically installed within 200 feet or less of a small-radius curve or Stop sign or, if installed on a street with a significant downgrade, at the top of a hill" Refer to Module 4 for additional data
Vehicle Volume	As single installation, there is little traffic diversion from the street; as part of a series, typical volume reductions of 20 percent observed Refer to Module 4 for additional data
Pedestrian Safety and Mobility	Appropriate location for a crosswalk; in traffic calming terms, a crosswalk on a speed table is called a raised crosswalk [provide link to section 3.14] Refer to Module 6 for additional discussion
Bicyclist Safety and Mobility	Bicyclist safety should not be affected; some jurisdictions use a maximum street grade of 5 percent if the street is designated as a bicycle route Bicyclist can negotiate a speed table with little delay or discomfort; it is also possible to bypass speed table by passing through the gap between the table and the curb and gutter
Motorist Safety and Mobility	Produces sufficient discomfort to a motorist driving above the speed table design speed to discourage speeding Can be constructed with brick or other textured materials on the flat section
Emergency Vehicle Safety and Mobility	Less speed delay than for a speed hump Has less jarring effect on long, stiff-bodied emergency service vehicle than speed hump Refer to Module 5 for additional discussion
Large Vehicle Safety and Mobility	Larger vehicle typically crosses at slower speed than does a personal passenger motor vehicle Refer to Module 5 for additional discussion
Accessibility of Adjacent Property	May result in the removal of on-street parking adjacent to speed table, on both sides of the street Should be placed at least five feet from a driveway for comfort
Environment	Potential for increased noise due to vehicle braking and accelerating and to the vibration of loose items in truck beds or trailers
Design Issues	Placement factors include vertical and horizontal alignment of street, proximity to nearest intersection, location of driveways and on-street parking, presence or absence of street lighting, location of designated pedestrian crossings, drainage, and utility access points (drains, valves, etc.) Should not be located as to require the relocation of above-ground and below-ground utilities A speed table does not extend from curb to curb Typically, does not interfere with drainage because table does not extend from curb to curb; however, if drainage gutter or flow of water is in the center of the roadway, drainage and hydraulic impacts need to be evaluated

Figure 3.12.3. Speed Table in a Series
(Source: James R. Barrera)

ADDITIONAL DESIGN CONSIDERATIONS

Most agencies implement speed tables with a height of between 3 and 3.5 inches and an overall travel length of 22 feet. The most common speed table consists of a 10 foot plateau with 6 foot approaches on both sides that can be straight, parabolic or sinusoidal in profile. Speed tables with heights as great as 6 inches, ramps of up to 10 feet, and plateaus between 18 and 23 feet in length have been tested and found to better accommodate large vehicles with long wheelbases (such as fire trucks and transit buses).

A speed table should be clearly marked, so all roadway users are able to anticipate it and reduce their speeds appropriately.

[The primary difference between a speed table design and a raised crosswalk design is the height and manner in which it meets the curb: with or without a side taper.]

3.13 Offset Speed Table

DESCRIPTION AND GENERAL PURPOSE

An offset speed table is a raised area placed across the roadway designed to physically limit the speed at which a vehicle can traverse it. Like a speed table, it extends across the travelway and has a long enough flat top (typically, 10 feet) to accommodate the entire wheelbase of most passenger cars.

The offset speed table is split down the centerline of the street with the two halves separated longitudinally (as shown in Figure 3.13.1). The offset tables enable an emergency response vehicle to bypass the speed tables by travelling in the opposing traffic lane for a short distance. This maneuver removes most of the emergency vehicle delay associated with a standard speed table.

Figure 3.13.1. Offset Speed Table
(Source: Jeff Gulden)

APPROPRIATE APPLICATION

Appropriate Application – Offset Speed Table
Type of Street	Can be installed on a local street, collector street, and in certain circumstances, an arterial street
Intersection or Roadway Segment	Placed at a midblock location; Pennsylvania recommends a distance of 150 feet from an unsignalized intersection and 250 feet from a signalized intersection Should not be placed on a sharp curve; ITE Guidelines for the Design and Application of Speed Humps recommends a minimum horizontal curve radius of 300 feet
Roadway Cross-Section	Appropriate for a two-lane two-way street Typically installed with an urban cross-section (i.e., curb and gutter)¹⁴ but an open section can be acceptable Can be applied both with and without sidewalks or bicycle facilities
Speed Limit	ITE Guidelines for the Design and Application of Speed Humps recommends consideration only on a street with a posted speed limit of 30 mph or less; many jurisdictions follow the same maximum (e.g., South Carolina, Pennsylvania); others have chosen a 35 mph maximum (e.g., Delaware, Pasadena) Generally not appropriate when the pre-implementation 85th percentile speed is 45 mph or more
Vehicle Traffic Volume	Some jurisdictions provide guidance on a maximum traffic volume that can be properly accommodated; Pennsylvania sets a maximum daily volume of 3,500; South Carolina uses a maximum of 4,000; Pasadena, CA uses a maximum of 4,000, with at least 1,000 vehicles in each direction ITE Guidelines for the Design and Application of Speed Humps recommends consideration if no more than five percent of the overall traffic flow consists of long-wheelbase vehicles
Emergency Route	Can be appropriate for a primary emergency vehicle route or street that provides access to a hospital or emergency medical services; another form of vertical deflection – a speed cushion – could also be appropriate
Transit Route	Generally not appropriate for a bus transit route with BRT, Express, or Limited Stop service (unless the posted speed limit is 30 mph or less); speed cushion could be appropriate Can be appropriate along a neighborhood circulator or other local bus service route Should not be located near bus stop to ensure passengers are not transitioning between standing and sitting as the bus crosses over the offset speed table
Access Route	Not appropriate along the primary access to a commercial or industrial site
Grade	Can be installed on, or beyond, a crest vertical curve only if there is adequate stopping sight distance or warning signs are provided ITE Guidelines for the Design and Application of Speed Humps recommends consideration only with a grade of 8 percent or less; many jurisdictions adhere to that maximum grade (e.g. Pennsylvania, South Carolina) but others follow a lower maximum: Delaware – 6 percent; Minnesota – 5 percent

¹⁴ If the street does not have curbing, an obstruction such as signing, flexible delineator posts, or bollards may be acceptable to prevent a motorist from driving around the table. Potentially hazardous objects (e.g., rocks, boulders) should not be used.

EFFECTS AND ISSUES

Effects and Issues – Offset Speed Table
Vehicle Speed	Single offset speed table reduces 85^th percentile speeds to the range of 20 to 30 mph when crossing the table; speed reduction effects decline at the rate of approximately 0.5 to 1 mph every 100 feet beyond the 200 foot approach and exit of a speed table; in order to retain slower vehicle speeds over a longer distance, a series of speed tables is needed ITE Guidelines for the Design and Application of Speed Humps recommends a spacing of between 260 and 500 feet; some jurisdictions have refined these guidelines: Pennsylvania – spacing between 250 and 600 feet South Carolina – spacing of no less than 350 feet Virginia – spacing of approximately 500 feet, with clear visibility of 200 feet, and placement no closer than 200 feet from an intersection Pasadena – only on a street segment that is at least 1,200 feet in length and on which any traffic signals or Stop signs are at least 1,200 feet apart Proper placement of the initial speed table in a series is significant; ITE Guidelines for the Design and Application of Speed Humps recommends "the first speed [table] in a series is normally located in a position where it cannot be approached at high speed from either direction; to achieve this objective, it is typically installed within 200 feet or less of a small-radius curve or Stop sign or, if installed on a street with a significant downgrade, at the top of a hill" Refer to Module 4 for additional data
Vehicle Volume	As single installation, there is little traffic diversion from the street; as part of a series, typical volume reductions of 20 percent observed Refer to Module 4 for additional data
Pedestrian Safety and Mobility	Not a preferred location for a crosswalk
Bicyclist Safety and Mobility	Bicyclist safety should not be affected; some jurisdictions use a maximum street grade of 5 percent if the street is designated as a bicycle route Bicyclist can negotiate a speed table with little delay or discomfort; it is also possible to bypass speed table by passing through the gap between the table and the curb and gutter
Motorist Safety and Mobility	Produces sufficient discomfort to a motorist driving above the speed table design speed to discourage speeding Can be constructed with brick or other textured materials on the flat section
Emergency Vehicle Safety and Mobility	Minimal delay for emergency service vehicle that bypasses tables Refer to Module 5 for additional discussion
Large Vehicle Safety and Mobility	Larger vehicle typically crosses at slower speed than does a personal passenger motor vehicle Refer to Module 5 for additional discussion
Accessibility of Adjacent Property	May result in the removal of on-street parking adjacent to offset speed table, on both sides of the street Should be placed at least five feet from a driveway for comfort
Environment	Potential for increased noise due to vehicle braking and accelerating and to the vibration of loose items in truck beds or trailers
Design Issues	Placement factors include vertical and horizontal alignment of street, proximity to nearest intersection, location of driveways and on-street parking, presence or absence of street lighting, location of designated pedestrian crossings, drainage, and utility access points (drains, valves, etc.) Driver circumnavigation can be minimized with small median islands leading up to each table, with double-centerline and raised pavement markers Should not be located as to require the relocation of above-ground and below-ground utilities Typically, does not interfere with drainage; but roadway, drainage and hydraulic impacts should be evaluated

ADDITIONAL DESIGN CONSIDERATIONS

The spacing between offset speed tables is typically a minimum of 50 feet (measured between the closest taper edges).

Typical height of offset speed tables is between 3 and 3.5 inches, with an overall travel length of 22 feet. The most common speed table consists of a 10 foot plateau with 6 foot approaches on both sides that can be straight, parabolic or sinusoidal in profile. Speed tables with heights as great as 6 inches, ramps of up to 10 feet, and plateaus between 18 and 23 feet in length have been tested and found to better accommodate large vehicles with long wheelbases (such as fire trucks and transit buses).

An offset speed table should be clearly marked, so all roadway users are able to anticipate it and reduce their speeds appropriately.

3.14 Raised Crosswalk

DESCRIPTION AND GENERAL PURPOSE

A raised crosswalk is a variation of a flat-topped speed table. A raised crosswalk is marked and signed as a pedestrian crossing. The 10-foot flat top on a typical speed table conforms to a desired crosswalk width (see Figure 3.14.1).

There are two distinct raised crosswalk designs. Both use a modified version of the common 22-foot speed table:

The most common type is constructed flush against the roadside curb.
The other type is constructed on an open section (requiring a curb ramp on the raised crosswalk) or separate from the curb (requiring a curb ramp on both the curb and the raised crosswalk).

A raised crosswalk improves pedestrian safety by causing motorist speed to decrease at the crossing (see Figure 3.14.2).

A raised crosswalk is typically between 3 and 6 inches above street level. It is common for a raised crosswalk to be level with the street curb. This height increases the visibility of a pedestrian in a crosswalk to a motorist. It also improves the line of sight for a pedestrian toward an oncoming vehicle.

A raised crosswalk can be placed midblock or at an intersection.

A stop-animation film that demonstrates the benefits of a raised crosswalk can be accessed at the following hyperlink: http://www.streetfilms.org/raised-crosswalk/ (Source: Streetfilms)

A video of pedestrians, bicyclists, and motor vehicles passing over a raised crosswalk can be accessed at the following hyperlink:

http://www.yargerengineering.com/articles/traffic calming.html#Raised crosswalk (Source: Yarger Engineering, Inc.)

Figure 3.14.1. Raised Crosswalk Schematic
(Source: Delaware Department of Transportation)

Figure 3.14.2. Typical Raised Crosswalk Application
(Source: Jeff Gulden)

APPROPRIATE APPLICATION

Appropriate Application – Raised Crosswalk
Type of Street	Appropriate if there is an existing crosswalk in the approximate crossing location or if a crosswalk is warranted based on local standards and criteria Generally installed on a residential local street or a collector street (or on a low-speed arterial street through a commercial district)
Intersection or Roadway Segment	Can be placed at a midblock location (see Figure 3.14.3) or at an intersection (see Figure 3.14.4) Should not be placed on a sharp curve; ITE Guidelines for the Design and Application of Speed Humps recommends a minimum horizontal curve radius of 300 feet
Roadway Cross-Section	Can be used on a single-lane one-way or two-lane two-way street Typically installed with an urban cross-section (i.e., curb and gutter)¹⁵ but an open section can be acceptable Cross-section can include on-street parking Can be applied both with and without sidewalks or bicycle facilities
Speed Limit	ITE Guidelines for the Design and Application of Speed Humps recommends consideration only on a street with a posted speed limit of 30 mph or less; many jurisdictions follow the same maximum (e.g., South Carolina, Pennsylvania); others have chosen a 35 mph maximum (e.g., Delaware, Pasadena) Generally not appropriate when the pre-implementation 85th percentile speed is 45 mph or more
Vehicle Traffic Volume	A maximum traffic volume could be appropriate if the raised crosswalk functions more as a speed table; however, many raised crosswalks are installed at locations with high pedestrian volume, high vehicle volume, and low vehicle speed (for example, in a downtown)
Emergency Route	Generally not appropriate for a primary emergency vehicle route or street that provides access to a hospital or emergency medical services
Transit Route	Can be appropriate for a bus transit route if typical bus operating speeds are in 25 mph range Should not be located near bus stop to insure passengers are not transitioning between standing and sitting as the bus crosses over raised crosswalk
Access Route	Not appropriate along the primary access to a commercial or industrial site
Grade	Can be installed on a crest vertical curve only if there is adequate stopping sight distance or appropriate warning signs provided ITE Guidelines for the Design and Application of Speed Humps recommends consideration only with a grade of 8 percent or less; many jurisdictions adhere to that maximum grade (e.g. Pennsylvania, South Carolina; Portland OR) but others follow a lower maximum: Delaware – 6 percent; Minnesota – 5 percent

¹⁵ If the street does not have curbing, an obstruction such as signing, flexible delineator posts, or bollards may be acceptable to prevent a motorist from driving around the table. Potentially hazardous objects (e.g., rocks, boulders) should not be used.

Figure 3.14.3. Raised Crosswalk Midblock
(Source: R. Goldberg)

Figure 3.14.4. Raised Crosswalk at Intersection
(Source: City of Cambridge, Massachusetts)

EFFECTS AND ISSUES

Effects and Issues – Raised Crosswalk
Vehicle Speed	Single raised crosswalk reduces 85^th percentile speeds to the range of 20 to 30 mph when crossing the crosswalk; speed reduction effects decline at the rate of approximately 0.5 to 1 mph every 100 feet beyond the 200 foot approach and exit of a raised crosswalk; in order to retain slower vehicle speeds over a longer distance, a series of speed tables or raised crosswalks is needed ITE Guidelines for the Design and Application of Speed Humps recommends a spacing of between 260 and 500 feet; some jurisdictions have refined these guidelines: Pennsylvania – spacing between 250 and 600 feet South Carolina – spacing of no less than 350 feet Virginia – spacing of approximately 500 feet, with clear visibility of 200 feet, and placement no closer than 200 feet from an intersection Pasadena – only on a street segment that is at least 1,200 feet in length and on which any traffic signals or Stop signs are at least 1,200 feet apart Proper placement of the initial raised crosswalk in a series is significant; ITE Guidelines for the Design and Application of Speed Humps recommends "the first [raised crosswalk] in a series is normally located in a position where it cannot be approached at high speed from either direction; to achieve this objective, it is typically installed within 200 feet or less of a small-radius curve or Stop sign or, if installed on a street with a significant downgrade, at the top of a hill" Refer to Module 4 for additional data
Vehicle Volume	As single installation, there is little traffic diversion from the street; as part of a series, typical volume reductions of 20 percent observed Refer to Module 4 for additional data
Pedestrian Safety and Mobility	Pedestrian safety improved because (1) vehicle speed is lowered at crosswalk, (2) pedestrian in a raised crosswalk is more visible to an oncoming motorist and (3) pedestrian has an elevated view of oncoming traffic; raised crosswalk could be combined with a curb extension to provide additional visibility for pedestrian (see Figure 3.14.5) If raised crosswalk is the same height as the curb, edge of the raised crosswalk should be differentiated with a detectable warning or truncated domes to warn a person with a visual impairment Refer to Module 6 for additional discussion
Bicyclist Safety and Mobility	Bicyclist safety should not be affected; some jurisdictions use a maximum street grade of 5 percent if the street is designated as a bicycle route Bicyclist can negotiate a raised crosswalk with little delay or discomfort (see Figure 3.14.6)
Motorist Safety and Mobility	Produces sufficient discomfort to a motorist driving above the raised crosswalk design speed to discourage speeding
Emergency Vehicle Safety and Mobility	Less speed delay than for a speed hump Has less jarring effect on long, stiff- bodied emergency service vehicle Refer to Module 5 for additional discussion
Large Vehicle Safety and Mobility	Larger vehicle typically crosses at slower speed than does a personal passenger motor vehicle Refer to Module 5 for additional discussion
Accessibility of Adjacent Property	May result in the removal of on-street parking adjacent to raised crosswalk, on both sides of the street Typically placed at least five feet from a driveway but can be designed to incorporate a driveway
Environment	Potential for increased noise due to vehicle braking and accelerating and to the vibration of loose items in truck beds or trailers
Design Issues	Placement factors include vertical and horizontal alignment of street, proximity to nearest intersection, location of driveways and on-street parking, presence or absence of street lighting, location of designated pedestrian crossings, drainage, and utility access points (drains, valves, etc.) Extends from curb to curb and therefore affects surface drainage on the roadway; likely that a catch basin will be required on the upstream side of the raised crosswalk; drainage and hydraulic impacts need to be evaluated Should not be located as to require the relocation of above-ground and below-ground utilities

Figure 3.14.5. Raised Crosswalk with Curb Extension
(Source: Scott Batson)

Figure 3.14.6. Raised Crosswalk with Bicycle Lane
(Source: Scott Batson)

ADDITIONAL DESIGN CONSIDERATIONS

The primary difference between a speed table design and a raised crosswalk design is the height and manner in which it meets the curb.

Most agencies implement raised crosswalks with a height of between 3 and 3.5 inches and an overall travel length of 22 feet. The most common raised crosswalk consists of a 10 foot plateau with 6 foot approaches on either side that can be straight, parabolic, or sinusoidal in profile.

A raised crosswalk requires incorporation of all the standard crosswalk design elements. The markings must be visible to motorists, especially at night.

For a raised crosswalk, the longitudinal drainage taper can be removed to form a level pedestrian crossing. Drainage will still need to be provided, such as by using a trench drain through the raised crosswalk and covered with an ADA-compliant grate (see Figure 3.14.7). Another option is to place the drainage inlet upstream of the raised crosswalk.

A raised crosswalk should be clearly marked, so all roadway users are able to anticipate it and reduce their speeds appropriately.

So that a person with visual impairment can differentiate the roadway from the sidewalk at a raised crosswalk, color contrasts and detectable warnings or truncated domes at edges can enable a pedestrian with a vision impairment to detect the crossing.

A sample design for a raised crosswalk is presented in Figure 3.14.8.

Figure 3.14.7. Raised Crosswalk Design to Accommodate Drainage
(Source: Jeff Gulden)

Figure 3.14.8. Sample Design for Raised Crosswalk
(Source: Delaware Department of Transportation)

3.15 Raised Intersection

DESCRIPTION AND GENERAL PURPOSE

A raised intersection is a flat, raised area covering an entire intersection with ramps on all approaches. It is essentially a speed table that covers an entire intersection, including the crosswalks (see Figure 3.15.1).

The purpose of a raised intersection is to slow vehicle traffic through the intersection and to improve safety for pedestrians. It has the advantage of calming two streets at once.

A raised intersection typically rises to sidewalk level.

A raised intersection is especially applicable in a dense urban area (see Figure 3.15.2). A typical installation is at a signal-controlled or all-way stop-controlled intersection with a large volume of street-crossing pedestrians. A raised intersection reinforces the need for a motorist to drive cautiously and be wary of crossing pedestrians.

[A raised intersection is also called a raised junction, intersection hump, or plateau.]

[Two field studies of five raised intersections measured reductions between 1 and 5 mph for 85^th percentile speeds (Source: FHWA, Engineering Speed Management Countermeasures: A Desktop Reference of Potential Effectiveness in Reducing Speed, July 2014) https://www.highways.dot.gov/safety/speed-management/engineering-speed-management-countermeasures]

A video of pedestrians, bicyclists, and motor vehicles passing over a raised intersection can be accessed at the following hyperlink:

http://www.yargerengineering.com/articles/traffic calming.html#Raised intersections (Source: Yarger Engineering, Inc.)

Figure 3.15.1. Raised Intersection
(Source: Yarger Engineering, Inc.)

""Figure 3.15.2. Raised Intersection in Dense Urban Setting. This figure contains a picture of a two lane, one way road between two strands of palm trees and multi-story buildings. There is oncoming traffic in both lanes. Two entrances to the raised intersection can be seen. The intersection itself is done in light red brick.
Figure 3.15.2. Raised Intersection in Dense Urban Setting
(Source: Ian Lockwood)

APPROPRIATE APPLICATION

Appropriate Application – Raised Intersection
Type of Street	Appropriate if there are existing crosswalks on all four legs of the intersection or if crosswalks are warranted Appropriate for the intersection of collector, local, and residential subdivision streets Can be appropriate in both a residential setting (see Figure 3.15.3) and in a commercial business district Could be acceptable on a low-speed arterial in a downtown business district with significant pedestrian activity
Intersection or Roadway Segment	Placed at an intersection Can be a T-intersection or multi-leg intersection
Roadway Cross-Section	Approach legs can be either one-way or two-way Appropriate only with an urban cross-section (i.e., curb and gutter) that includes sidewalks on all sides of the intersection Can include on-site parking on the approach legs Appropriate if a bicycle facility passes through the intersection
Speed Limit	Maximum speed limit of 30 mph based on ITE Guidelines for the Design and Application of Speed Humps and some jurisdictions (e.g., South Carolina, Pennsylvania); others use a 35 mph maximum (e.g., Delaware)
Vehicle Traffic Volume	Appropriate if the daily traffic volume on each intersection approach is relatively low; example thresholds include Pennsylvania with a maximum of 10,000 vehicles per day and South Carolina which uses 4,000 on each leg in a residential setting and 6,000 on each leg in a commercial area
Emergency Route	Can be an appropriate application for a primary emergency vehicle route or on street that provides access to a hospital or emergency medical services
Transit Route	Can be an appropriate application for a bus transit route
Access Route	Generally not appropriate along the primary access to a commercial or industrial site
Grade	Can be installed on a crest vertical curve only if there is adequate stopping sight distance or if appropriate warning signs are provided Maximum grade of 8 percent recommended in ITE Guidelines for the Design and Application of Speed Humps and used by some jurisdictions (e.g., Pennsylvania, South Carolina); Delaware uses a maximum of 6 percent; Minnesota uses a maximum of 5 percent

Figure 3.15.3. Raised Intersection in Residential Setting without Raised Crosswalks
(Source: Google Street View)

EFFECTS AND ISSUES

Effects and Issues – Raised Intersection
Vehicle Speed	A single raised intersection reduces 85^th percentile speeds to the range of 25 to 35 mph when crossing the intersection; vehicle speeds at some distance from the intersection have not been shown to change appreciably
Vehicle Volume	As a single installation, there is little traffic diversion from the intersection
Pedestrian Safety and Mobility	Pedestrian safety is improved because a pedestrian is more visible to an oncoming motorist and the pedestrian has an elevated view of oncoming traffic (see Figure 3.15.4) If the same height as the curb, the edge of the raised intersection should be differentiated with a tactile measure to warn a person with a visual impairment Refer to Module 6 for additional discussion
Bicyclist Safety and Mobility	Should not be affected by a raised intersection unless pavers (or some other textured surface) are used
Motorist Safety and Mobility	Produces sufficient discomfort to a motorist driving above the raised intersection design speed to discourage speeding
Emergency Vehicle Safety and Mobility	A large emergency vehicle typically crosses a raised intersection at a slower speed than does a personal passenger motor vehicle Refer to Module 5 for additional discussion
Large Vehicle Safety and Mobility	A larger vehicle typically crosses a raised intersection at a slower speed than does a personal passenger motor vehicle; a typical raised intersection delay for a large commercial vehicle is in the range of 2 to 6 seconds Refer to Module 5 for additional discussion
Accessibility of Adjacent Property	Should not result in any change in accessibility to property along all legs of the intersection; on-street parking restrictions and driveway accessibility should be the same whether intersection is raised or level
Environment	Can serve as a form of gateway treatment at or near the entrance to an area for which traffic calming is desired Traffic noise may increase from braking and acceleration of vehicles
Design Issues	Likely requires changes in access to below-ground utilities Requires redesign of surface drainage structures that serve the intersection and approach legs

Figure 3.15.4. Raised Intersection with Raised Crosswalks
(Source: Google Street View)

ADDITIONAL DESIGN CONSIDERATIONS

The design of a raised intersection needs to pay close attention to the existing drainage systems because the grade of the entire intersection will be raised. Additional (or relocated) drainage inlets will likely be required.

In order to enable a pedestrian with a visual impairment to differentiate between the roadway and the sidewalk, measures such as color contrasts and detectable warning truncated domes at edges must be included.

A minimum pavement slope of 1 percent (or the local practice standard) should be provided within the raised intersection to facilitate surface drainage. Surface drainage implications on the approaches to a raised intersection should also be addressed.

A sample design for a raised intersection is presented in Figure 3.15.5.

Figure 3.15.5. Sample Design for Raised Intersection
(Source: Delaware Department of Transportation)

3.16 Corner Extension/Bulbout

DESCRIPTION AND GENERAL PURPOSE

[Other terms include neckdown, corner extension, pop-out, bump out, knuckle and nub. If coupled with a crosswalk, a roadway narrowing can be referred to as a safe cross. When placed at the entrance to a neighborhood, often with textured paving between a pair of them, a bulb-out or corner extension is called a gateway or entry feature.]

A curb extension is a horizontal extension of the sidewalk into the street resulting in a narrower roadway section (see Figure 3.16.1). This device may be used at either corner or midblock. A curb extension at an intersection is called a corner extension or bulbout. A curb extension located midblock is called a choker [provide link to section 3.17].

When combined with on-street parking, a corner extension can create a protected parking bay.

The effect of a corner extension on vehicle speeds is limited because of the absence of either a pronounced vertical or horizontal deflection. Its primary purpose is to "pedestrianize" an intersection. A corner extension (with a reduced corner radius) slows automobile turning speeds, shortens pedestrian crossing distance, and increases pedestrian visibility (see Figure 3.16.2).

When a corner extension is part of a downtown redevelopment project, it can go hand-in-hand with on-street parking bays and crosswalks (in "safe cross" designs).

A corner extension can be combined with a vertical speed control device (e.g., a raised crosswalk) to achieve a greater reduction in vehicle speed.

[Two field studies of five corner extensions measured reductions between 1 and 3.5 mph for 85^th percentile speeds (Source: FHWA, Engineering Speed Management Countermeasures: A Desktop Reference of Potential Effectiveness in Reducing Speed, July 2014) https://www.highways.dot.gov/safety/speed-management/engineering-speed-management-countermeasures]

Figure 3.16.1. Corner Extension Schematic
(Source: Delaware Department of Transportation)

Figure 3.16.2. Corner Extension with Shortened Pedestrian Crossing Distance
(Source: Hillary Orr)

APPROPRIATE APPLICATION

Appropriate Application – Corner Extension/Bulbout
Type of Street	Appropriate for all street classifications – arterial, collector, or local street Can be appropriate in both an urban and suburban setting (see Figures 3.16.3 and 3.16.4)
Intersection or Roadway Segment	Applicable only at an intersection; if placed midblock, considered a choker [provide link to section 3.17] Can be applied on any or all of the approach legs of an intersection with any number of legs
Roadway Cross-Section	Can be used on both one-way and two-way streets Can be installed only on a roadway with an urban cross-section (i.e., curb and gutter) Can be applied both with and without a bicycle facility Can be applied on a roadway with, and can protect, on-street parking
Speed Limit	Can be appropriate for any speed limit, provided an adequate shy distance is provided between the travel lane and the corner extension curb Pennsylvania uses a maximum of 40 mph provided travel lanes are not narrowed; Delaware uses 35 mph
Vehicle Traffic Volume	Can be appropriate at all levels of traffic volume; Pennsylvania permits daily volumes as high as 15,000 provided travel lanes are not narrowed
Emergency Route	Can be appropriate along a primary emergency vehicle route or street that provides access to a hospital or emergency medical services (if appropriate turning radii can be provided)
Transit Route	May not be appropriate where a bus turns along a transit route if an adequate turning radius cannot be provided; the stop bar on the opposite travel lane on the receiving leg of the intersection may need to be moved back in order to accommodate frequent transit vehicles making a turn; the number of turning transit vehicles and the total traffic volume on the receiving street are both factors when a corner extension is considered An extended length corner extension could enable a bus stop landing area for both front and back transit bus doors, thereby eliminating the need for a bus to pull out of (and pull back into) traffic A corner extension bus stop eliminates the need to remove on-street parking that would enable a transit vehicle to maneuver to and from the traditional curb
Access Route	Typically not appropriate along a primary access route to a commercial or industrial site if an adequate turning radius cannot be provided; the number of large turning vehicles and the total traffic volume on the receiving street are both factors when a corner extension is considered
Grade	Can be installed on a crest vertical curve only if there is adequate stopping sight distance or if appropriate warning signs are provided Maximum grade should comply with local standards and criteria; Delaware uses a maximum grade of 6 percent

Figure 3.16.3. Corner Extension in Urban Setting
(Source: Jennifer Rosales)

Figure 3.16.4. Corner Extension in Suburban Setting
(Source: www.pedbikeimages.org / Michael Austin)

EFFECTS AND ISSUES

Effects and Issues – Corner Extension/Bulbout
Vehicle Speed	Can slow traffic by funneling through narrower street opening than is provided in upstream cross-section; speeds likely to decrease slightly; amount of speed reduction depends on volume and distribution of traffic Speeds are reduced on intersection approach and through intersection area Shorter curb radius can slow turning vehicles; if large right-turning volume, could increase delay and lower speeds
Vehicle Volume	Has little effect on traffic volumes; access and turns are maintained and traffic speeds are not changed dramatically
Pedestrian Safety and Mobility	Shortens intersection crossing distance for a pedestrian; shorter distance reduces the potential for pedestrian-vehicle conflict and likely improves pedestrian safety Provides additional queuing space for pedestrians at corner Because corner extension is elevated above the vehicle travel lanes, improves line-of-sight for pedestrian at the corner and makes that pedestrian more visible to oncoming motorist; also enables pedestrian to stand at edge of parked vehicles, further increasing visibility Refer to Module 6 for additional discussion
Bicyclist Safety and Mobility	Should not extend into a bicycle lane (see Figure 3.16.5)
Motorist Safety and Mobility	Likely to have minimal effect on motorist mobility and safety Presence of physical feature reduces possibility of illegal parking close to intersection
Emergency Vehicle Safety and Mobility	Retains sufficient width to allow for continued easy flow of emergency vehicles Shortened curb radius may require emergency vehicle turning at intersection to swing across centerline Refer to Module 5 for additional discussion
Large Vehicle Safety and Mobility	Retains sufficient width to allow for continued easy flow of large vehicles like combination trucks Shortened curb radius may require large vehicle turning at intersection to swing across centerline Refer to Module 5 for additional discussion
Accessibility of Adjacent Property	May require removal of some on-street parking immediately adjacent to intersection
Environment	Can be used as a landscaping opportunity; many cities use bioswale curb extensions to capture stormwater (see Figure 3.16.6); if the corner extension includes a pedestrian crossing, the landscaping should be designed to not obstruct pedestrian visibility
Design Issues	Relocation of curbing and pedestrian queuing area may require relocation of drainage features such as catch basins, concrete channels, valley gutters, inlets, and trench drains May require relocation of above- and below-ground utilities

Figure 3.16.5. Corner Extension and Bicycle Lane
(Source: Scott Batson)

Figure 3.16.6. Corner Extension with Bioswale
(Source: Scott Batson)

ADDITIONAL DESIGN CONSIDERATIONS

The design of a corner extension needs to pay close attention to the existing drainage system because the gutter alignment will be altered (see Figure 3.16.7). A corner extension could necessitate a major utility relocation particularly if additional drainage inlets are required (see Figure 3.16.8).

A corner extension is typically constructed to a width of between 6 and 8 feet. It should be offset from the through traffic lane by 1.5 feet.

A sample design for a corner extension is presented in Figure 3.16.9.

Figure 3.16.7. Corner Extension with Realigned Gutter
(Source: Jeff Gulden)

Figure 3.16.8. Corner Extension with Drainage Structure Relocation
(Source: James R. Barrera)

)
Figure 3.16.9. Sample Design for Corner Extension
(Source: Delaware Department of Transportation)

3.17 Choker

DESCRIPTION AND GENERAL PURPOSE

A curb extension is a horizontal extension of the curb into the street resulting in a narrower roadway section. This device may be used at either corner or midblock. A curb extension located midblock is called a choker. A curb extension located at an intersection is called a corner extension or bulbout [provide link to section 3.16].

A choker is the narrowing of a roadway through the use of curb extensions or roadside islands (see Figure 3.17.1). It can be created by a pair of curb extensions at a midblock location that narrows the street by widening the sidewalk or planting strip at that location. A choker can also be created through the use of roadside islands. This narrowing is intended to discourage motorist speeding and to reduce vehicle speeds in general.

Within a choker on a two-way, two lane roadway, vehicles are able to pass each other without conflict. But the narrower cross-section lowers the margin of error for motorists who, as a result, tend to moderate their speed. In some applications, a double-lane choker is combined with a median island as a means to reduce the possibility of opposing vehicle conflicts.

A one-lane choker forces two-way traffic to take turns going through the pinch point. If the roadway is narrowed to a single lane, the lane can be either parallel to the initial roadway alignment or angled to the alignment. The former is called a parallel choker, the latter an angled choker, twisted choker, or angle point (see Figure 3.17.2).

A choker can be located at any spacing desired for traffic calming. A choker is often combined with on-street parking to create a protected parking bay.

Landscaping on a choker can make the traffic calming feature attractive and can make it more visible to the motorist.

A choker may be a good location to place a midblock crosswalk (either level with the roadway or as a raised crosswalk) because it shortens the distance a pedestrian walks on the travelway.

[Other terms for choker include pinch point, midblock narrowing, midblock yield point, constriction, or edge island. If the choker is marked with a crosswalk, it is sometimes called a safe cross.]

[Four field studies of 12 chokers measured reductions between 1 and 4 mph for 85^th percentile speeds (Source: FHWA, Engineering Speed Management Countermeasures: A Desktop Reference of Potential Effectiveness in Reducing Speed, July 2014) https://www.highways.dot.gov/safety/speed-management/engineering-speed-management-countermeasures]

Figure 3.17.1. Choker Schematic
(Source: Delaware Department of Transportation)

Figure 3.17.2. Angled Choker
(Source: Dan Burden)

APPROPRIATE APPLICATION

Appropriate Application – Choker
Type of Street	Appropriate for an arterial, collector, or local street – whether in an urban or suburban setting (see Figures 3.17.3 and 3.17.4)
Intersection or Roadway Segment	Applicable only midblock; if placed at an intersection, considered a corner extension/bulbout [provide link to section 3.16]
Roadway Cross-Section	Can be used on a one-lane, one-way and two-lane, two-way street Most easily installed on a roadway with an urban cross-section (i.e., curb and gutter) Can be applied both with and without a bicycle facility Can be applied on a street with, and can protect, on-street parking
Speed Limit	Can be appropriate for any speed limit, provided an adequate shy distance is provided between the travel lane and the choker curb; Pennsylvania uses a maximum of 40 mph provided travel lanes are not narrowed; Delaware uses 35 mph
Vehicle Traffic Volume	Can be appropriate at all levels of traffic volume
Emergency Route	Can be appropriate along a primary emergency vehicle route or street that provides access to a hospital or emergency medical services
Transit Route	Can be appropriate along a bus transit route
Access Route	Can be appropriate along a primary access route to a commercial or industrial site
Grade	Can be installed on a crest vertical curve only if there is adequate stopping sight distance or if appropriate warning signs are provided Maximum grade should comply with local standards and criteria; Delaware uses a maximum grade of 6 percent

Figure 3.17.3. Choker in Urban Commercial Setting
(Source: www.pedbikeimages.org / Dan Burden)

Figure 3.17.4. Choker in Suburban Residential Setting
(Source: Scott Wainwright)

EFFECTS AND ISSUES

Effects and Issues – Choker
Vehicle Speed	Can slow traffic by funneling through narrower street opening than is provided in upstream cross-section; traffic speeds likely to decrease slightly (see Figure 3.17.5) Amount of speed reduction depends on volume and distribution of traffic; reduction is lessened when (1) the volume of traffic is significantly higher in one direction than the other or (2) volumes are so low that the likelihood of a motorist encountering an opposing motorist within the narrowed area is low
Vehicle Volume	Has little effect on traffic volumes
Pedestrian Safety and Mobility	Shortens street crossing distance for a pedestrian; shorter distance reduces potential for pedestrian-vehicle conflict and likely improves pedestrian safety (see Figure 3.17.6) Because it is elevated above the vehicle travel lanes, improves line-of-sight for a pedestrian at the crossing and makes that pedestrian more visible to an oncoming motorist Refer to Module 6 for additional discussion
Bicyclist Safety and Mobility	May reduce travelway width and force bicyclist and motor vehicle to share travel lane; if the vehicle volume is high, use of shared lane markings (sometimes known as a sharrow) and "bike may use full lane" signage could be necessary and appropriate
Motorist Safety and Mobility	Likely to have minimal effect on motorist mobility and safety Minimal impact on motorist comfort Can serve as protection for downstream on-street parked vehicles
Emergency Vehicle Safety and Mobility	Retains sufficient width to allow for continued flow of emergency vehicles Refer to Module 5 for additional discussion
Large Vehicle Safety and Mobility	Retains sufficient width to allow for continued flow of large vehicles like combination trucks Refer to Module 5 for additional discussion
Accessibility of Adjacent Property	May require removal of some on-street parking; therefore, may slightly reduce accessibility of adjacent property
Environment	Can be used as landscaping opportunity; if the choker includes a pedestrian crossing, the landscaping should be designed to not obstruct pedestrian visibility
Design Issues	Relocation of curbing may require relocation of drainage features such as catch basins, concrete channels, valley gutters, inlets, and trench drains May require relocation of above- and below-ground utilities Where the crown of a street is steep, a choker may actually go "uphill" because the new curb is higher than the original curb; this has the potential to cause drainage problems both at the curb and on the sidewalk

Figure 3.17.5. Choker with Passing Traffic
(Source: James R. Barrera)

Figure 3.17.6. Choker with Pedestrian Crosswalk
(Source: Shawn Leight)

ADDITIONAL DESIGN CONSIDERATIONS

A choker can be created by either curb extensions or edge islands. A curb extension offers more opportunity for aesthetic enhancements through landscaping. But an edge island leaves existing drainage channels open, making it possible to provide a bicycle bypass lane on a street without curbside parking.

The curb extension for the choker is typically constructed to a width of between 6 and 8 feet (see Figure 3.17.7). It should be offset from the through traffic lane by 1.5 feet.

In order to comply with the International Fire Code, 20 feet is the recommended space for a fire truck with aerial bucket or ladder so the outriggers can be set up. This width also permits smooth personnel operation around the vehicle during an emergency call. For the passage of a fire truck, 12 feet is the minimum and 14 feet is recommended for the narrowest roadway section.

On a street with little bicycle traffic or a low motor vehicle volume, the probability is low that a vehicle and bicycle will meet at the choker. In that case, no special accommodation is likely necessary for bicyclists. However, on a street with a bicycle lane or on a street with higher volumes, either (1) provide a bypass lane for a bicyclist, separated from the main travel lane by a curb extension or (2) provide shared lane markings (sometimes known as a sharrow) and "bike may use full lane" signage.

A midblock location near a streetlight is preferred for a choker.

Edge line tapers should conform to the MUTCD taper formulas.

Any curb extension or edge island should include signs compliant with MUTCD guidance.

The length of a choker island should be at least 20 feet, the length of a single car. A choker may extend toward the centerline beyond any parking lane. A sample design for a choker is presented in Figure 3.17.8.

Figure 3.17.7. Choker Adjacent to On-Street Parking
(Source: Creative Commons / Richard Drdul)

Figure 3.17.8. Sample Design for Choker
(Source: Delaware Department of Transportation)

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Module 3: Toolbox of Individual Traffic Calming Measures Part 2

3.9 Roundabout

DESCRIPTION AND GENERAL PURPOSE

APPROPRIATE APPLICATION

EFFECTS AND ISSUES

ADDITIONAL DESIGN CONSIDERATIONS

3.10 Speed Hump

DESCRIPTION AND GENERAL PURPOSE

EFFECTS AND ISSUES

ADDITIONAL DESIGN CONSIDERATIONS

3.11 Speed Cushion

DESCRIPTION AND GENERAL PURPOSE

APPROPRIATE APPLICATION

EFFECTS AND ISSUES

ADDITIONAL DESIGN CONSIDERATIONS

3.12 Speed Table

DESCRIPTION AND GENERAL PURPOSE

APPROPRIATE APPLICATION

EFFECTS AND ISSUES

ADDITIONAL DESIGN CONSIDERATIONS

3.13 Offset Speed Table

DESCRIPTION AND GENERAL PURPOSE

APPROPRIATE APPLICATION

EFFECTS AND ISSUES

ADDITIONAL DESIGN CONSIDERATIONS

3.14 Raised Crosswalk

DESCRIPTION AND GENERAL PURPOSE

APPROPRIATE APPLICATION

EFFECTS AND ISSUES

ADDITIONAL DESIGN CONSIDERATIONS

3.15 Raised Intersection

DESCRIPTION AND GENERAL PURPOSE

APPROPRIATE APPLICATION

EFFECTS AND ISSUES

ADDITIONAL DESIGN CONSIDERATIONS

3.16 Corner Extension/Bulbout

DESCRIPTION AND GENERAL PURPOSE

APPROPRIATE APPLICATION

EFFECTS AND ISSUES

ADDITIONAL DESIGN CONSIDERATIONS

3.17 Choker

DESCRIPTION AND GENERAL PURPOSE

APPROPRIATE APPLICATION

EFFECTS AND ISSUES

ADDITIONAL DESIGN CONSIDERATIONS