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FHWA Highway Safety Programs

Module 1: Purpose and Organization of ePrimer

1.1 What is the Traffic Calming ePrimer?

The Federal Highway Administration (FHWA) and the Institute of Transportation Engineers (ITE) have collaborated to produce this Traffic Calming ePrimer. It documents the results of several decades of traffic calming experience in the U.S.

This ePrimer was produced by FHWA and ITE to meet the standards of both organizations. Information in the ePrimer has been reviewed and vetted by planners, engineers, and fire officials, among others.

This ePrimer is a free, online resource openly available for public use. Providing this ePrimer for free encourages further discussion of the use of traffic calming as one tool to increase the quality of life in urban, suburban, and rural areas by reducing automobile speeds and traffic volumes on neighborhood streets.

This ePrimer presents a thorough review of current traffic calming practice and contains the information needed to understand this complex field. This ePrimer builds upon information in Traffic Calming: State of the Practice (1999), the U.S. Traffic Calming Manual (2009), and numerous references and resources (described later in sections 2.6 and 2.7).

[The ePrimer does not constitute a standard, specification, or regulation. It does not create or confer any rights for or on any person or operate to bind the public. Images in the report are intended to serve as examples of the range of real world existing conditions. The images are not limited to best practices or approved designs and in some cases may reflect conditions that are not recommended.]

1.2 Traffic Calming Measures Included in ePrimer

For this ePrimer, traffic calming measures are grouped within four categories: horizontal deflection, vertical deflection, street width reduction, and routing restriction. The category descriptions and the measures they include are presented below.

A horizontal deflection hinders the ability of a motorist to drive in a straight line by creating a horizontal shift in the roadway. This shift forces a motorist to slow the vehicle in order to comfortably navigate the measure. The types of horizontal deflections described in this ePrimer are:

  • Lateral shift
  • Chicane
  • Realigned intersection
  • Traffic circle, as illustrated in Figure 1.1
  • Small modern roundabout and mini-roundabout
  • Roundabout

Figure 1.1. Horizontal Deflection Measure - Traffic Circle. Please see the Extended Text Description below. This figure contains a photograph of a traffic circle as a horizontal deflection measure. The center of the traffic circle contains trees, shrubs and a sign showing a curved line with three arrows coming off of it, indicating the exits from the circle. Oncoming traffic includes a gray truck and a white car
Figure 1.1. Horizontal Deflection Measure - Traffic Circle

A vertical deflection creates a change in the height of the roadway that forces a motorist to slow down in order to maintain an acceptable level of comfort. The types of vertical deflections described in this ePrimer are:

  • Speed hump
  • Speed cushion, as illustrated in Figure 1.2
  • Speed table
  • Offset speed table
  • Raised crosswalk
  • Raised intersection

Figure 1.2. Vertical Deflection Measure - Speed Cushion. This figure contains a photograph which illustrates a wide residential street free of traffic. Three speed cushions are present, each a small change in height and painted with white indicator arrows showing right of way.
Figure 1.2. Vertical Deflection Measure – Speed Cushion
(Source: Jeff Gulden)

A street width reduction narrows the width of a vehicle travel lane. As a result, a motorist slows the vehicle in order to maintain an acceptable level of comfort and safety. The measure can also reduce the distance a pedestrian walks to cross a street, reducing exposure to pedestrian/vehicle conflicts. The types of street width reductions included in this ePrimer are:

  • Corner extension (i.e., a curb extension at an intersection)
  • Choker (i.e., a midblock curb extension)
  • Median island, as illustrated in Figure 1.3
  • On-street parking
  • Road diet

Figure 1.3. Street Width Reduction Measure - Median Island. This figure contains a photograph which illustrates a median island which contains landscaping including a palm tree and several low shrubs. A white sign also indicates right of way with an arrow passing around the right hand side of the median. A yellow reflective diamond is placed under the right of way sign.
Figure 1.3. Street Width Reduction Measure - Median Island
(Source: Ken Sides)

A routing restriction prevents particular vehicle movements at an intersection and is intended to eliminate some portions of cut-through traffic. The types of routing restrictions described in this ePrimer are:

  • Diagonal diverter
  • Full closure
  • Half closure, as illustrated in Figure 1.4
  • Median barrier
  • Forced turn island

Figure 1.4. Routing Restriction Measure - Half Closure. This figure contains a photograph which illustrates a half closure, restricting access down a two lane residential street to bicycles only. A concrete square filled with rocks is a physical barrier. A signpost holds four street signs (from top to bottom): a square white sign with a red circle containing the words Do Not Enter, a white rectangular sign with the words Except Bikes, a yellow sign with a double headed black arrow pointing left to right, and a red triangle covered in blue graffitti. There is also a railroad crossing in the near distance.
Figure 1.4. Routing Restriction Measure - Half Closure
(Source: Jeff Gulden)

The measures covered in this ePrimer are commonly used with the express purpose of supporting the livability and vitality of a residential or commercial area through an improvement in non-motorist safety, mobility, and comfort. Only measures that are self-enforcing and for which long-standing benefits have been measured are included.

1.3 Measures Not Included in ePrimer

A variety of other measures have been part of traffic calming installations in jurisdictions throughout the United States. These measures are not included in this ePrimer for a variety of reasons, including:

  • The measure is a standard traffic control measure typically used for improving traffic flow and has a secondary benefit for non-motorist safety.
  • The measure produces only a temporary or short-lived benefit.
  • The measure requires enforcement.
  • The measure has minimal or no measurable effect on vehicle speed or non-motorist safety.

The excluded measures include:

  • Signs (Stop, Yield, turn prohibition, traffic calmed neighborhood, through traffic prohibition, one-way, speed limit, commercial vehicle restriction, motorist feedback)
  • Pavement markings (marked crosswalk, pavement color change, narrowed lanes, transverse markings, school zones)
  • Gateways
  • Corner radius reduction
  • Textured pavement and rumble strips
  • Streetscaping/landscaping

Although this ePrimer focuses on mostly physical measures to calm traffic, non-physical measures can also be an effective part of traffic calming. For example, educational and enforcement efforts have long been used as part of a neighborhood traffic calming program and should continue to be considered as either supplements to self-enforcing physical means or as a precursor to physical measures. The application examples presented in Module 8 include a variety of education and enforcement techniques that have been used.

1.4 Terminology

The terminology used to describe various aspects of traffic calming can vary. Unlike other aspects of traffic engineering, where a slight variance in a term can change the entire meaning, traffic calming has been known to use multiple terms interchangeably. This ePrimer does not intend to force upon readers one terminology over another, as it is understood that agencies may prefer different terms. However, for consistency across this ePrimer, the following traffic calming-specific terms are used:

  • Traffic calming "measures" are the individual traffic calming elements that are implemented on a roadway. The term traffic calming "devices" or "features" are sometimes also used in practice.
  • Toolbox is a term commonly associated with traffic calming, used to describe the traffic calming measures that are available for use when developing traffic calming plans.
  • Neighborhood traffic calming, also referred to as neighborhood traffic management or residential traffic management, is the effort of traffic calming a primarily residential area.
  • Neighborhood traffic calming program is the overriding document that lays out the framework and systematic procedures for implementing traffic calming. The program typically covers an entire city (or county) and contains the process for traffic calming plan initiation, development, and implementation as well as the toolbox of traffic calming measures.
  • Neighborhood traffic calming plan identifies where individual traffic calming measures will be implemented and can cover an entire neighborhood or a single street. The plan may also include procedures for education and enforcement of traffic calming.

1.5 Organization of ePrimer

The ePrimer is presented in eight distinct modules (including this introduction) developed to allow the reader to move between each to find the desired information, without a cover-to-cover reading. Summaries of the modules are presented below.

Module 2. Traffic Calming Basics

This module presents a definition of traffic calming, the purpose of traffic calming, and the relationship of traffic calming to other transportation initiatives (like complete streets and context sensitive solutions).

Module 3. Individual Traffic Calming Measures

Descriptions of individual traffic calming measures are included in this module. Planners, engineers, decision makers, and residents can use this information when developing traffic calming plans. For each device, a description, general cost, factors to consider for its appropriate application, effects and issues to consider, and design and installation specifics are presented.

Module 4. Effects of Traffic Calming Measures on Motor Vehicle Speeds and Volume

Results from research on the effects of traffic calming measures on motor vehicle speed and volume are presented in this module. The information can be used to supplement individual traffic calming measure discussions in Module 3.

Module 5. Effects of Traffic Calming Measures on Non-Personal Passenger Vehicles

Traffic calming can affect all roadway users, including non-personal passenger vehicles. This module discusses the impacts that traffic calming measures can have on other roadway users, such as emergency response (fire, police, and ambulance services), public transit, and waste collection vehicles. Snow removal issues associated with traffic calming are also discussed.

Module 6. Effects of Traffic Calming Measures on Non-Motorized Users

Non-motorized users (e.g., bicyclists, pedestrians, persons in wheelchairs) can be affected by traffic calming. Accommodations for non-motorized users in traffic calming are discussed in this module.

Module 7. Traffic Calming Programs and Planning

This module provides examples and case studies of both comprehensive neighborhood traffic calming programs and neighborhood-specific traffic calming plans. Detail is provided on many aspects of development of a program and plans, with specifics on traffic calming warrants/criteria, top-down (data-driven) or bottom-up (application-driven)

approaches, packaging of complementary measures, design fatal flaws, and funding, among others. In addition, the module contains a section devoted to the legal authority and liability issues associated with traffic calming.

Module 8. Traffic Calming Case Studies

This module presents five case studies that cover both (1) effective processes used to plan and define a local traffic calming program or project and (2) assessments of the effects of individual and series of traffic calming measures