Retroreflective Borders on Traffic Signal Backplates

Original publication: Retroreflective Borders on Traffic Signal Backplates – A South Carolina Success Story; FHWA-SA-09-011; 2009(PDF, 377kB)

Red-light running is estimated to cause more than 200,000 crashes, 170,000 injuries, and approximately 900 deaths per year (Source: Federal Highway Administration, Red-Light Running Web Site (2008)). One of the reasons for the high number of crashes is driver inability or failure to see the traffic control device in time to comply. The South Carolina DOT (SCDOT) was concerned about the high number of crashes at some of its urban signalized intersections. It recognized that poor signal visibility can cause crashes. In response, SCDOT installed retroreflective borders on existing signal backplates at three intersections in the Columbia area that were experiencing a high incidence of crashes, many with injuries.

Key Accomplishments

The SCDOT experience demonstrates that low-cost improvements can effectively improve safety and reduce traffic crashes and their resulting injuries.

Results

The retroreflective borders installed at these Columbia signalized intersections cumulatively reduced total crashes by approximately 28.6 percent, injury crashes by 36.7 percent, and late-night/early morning crashes by 49.6 percent per year.

Contact

Joey D. Riddle
SCDOT
RiddleJD@dot.state.sc.us

Enhanced Signs and Markings at Stop Sign-Controlled Intersections

Original publication: Stop Sign-Controlled Intersections: Enhanced Signs and Markings: A Winston-Salem Success Story; FHWA-SA-09-010; 2009 (PDF, 355kB)

Stop signs are the primary form of traffic control at intersections across the United States. However, intersections controlled by stop signs account for one-third of all intersection crashes and more than 40 percent of fatal crashes (Source: Insurance Institute for Highway Safety, Volume 37, No 9, October 26, 2000). The City of Winston-Salem, North Carolina, was concerned about the high number of crashes at some of its intersections controlled by stop signs. It recognized that poor sign visibility and inadequate markings can cause crashes.

The city of Winston-Salem installed additional and larger stop signs, “Stop Ahead” advance traffic control signs, and clearly visible centerline markings and stop bars in various combinations at 16 intersections experiencing a high incidence of crashes, many with injuries.

Key Accomplishments

The Winston-Salem experience demonstrates that low-cost improvements can effectively improve safety and reduce traffic crashes and their resulting injuries and/or fatalities.

Results

The combinations of these enhanced countermeasures installed at the 16 Winston-Salem stop-controlled intersections cumulatively reduced total crashes by approximately 55 percent and total injuries by an average of 70 percent per year.

Contact

Stanley Polanis
Director of Transportation
City of Winston-Salem, NC
336-747-6867
stanp@cityofws.org

Safety Warrants and Spot Safety Index

Original publication: HSIP Noteworthy Practice Series, HSIP Project Identification; FHWA-SA-11-02; 2011(PDF, 2.7MB)

The North Carolina Department of Transportation (NCDOT) started to identify shortcomings in its problem identification method in the mid-1990s. The previous method focused on identifying locations with a potential safety issue based on factors such as crash frequency, crash rate, and crash severity. In many cases, the locations identified did not exhibit a correctable crash type and were congestion related issues. For example, NCDOT repeatedly identified signalized intersections exhibiting a high frequency of rear-end collisions, but attributed the collisions to congestion and driver inattention rather than a roadway factor.

Intersection Warrants:

I-1: Frontal Impact

I-2: Last Year Increase

I-3: Frequency with Severity Index Min

I-4: Night Location without Streetlight

I-5: Chronic Pattern

Section Warrants:

S-1: Run Off Road- Wet Conditions

S-2: Run Off Road

S-3: Wet Road Conditions

S-4: Non-Intersection Night Location without Streetlight

Bridge Warrant:

B-1: Bridge

Bike/Ped Intersection Warrants:

P-1: Last 3 Years (pedestrians)

P-2: Darkness with Streetlights

P-3: Alcohol Involvement

P-4: Chronic Location

X-1: Last 3 years (bicyclists)

X-2: Darkness with Streetlights

X-3: Alcohol Involvement

X-4: Chronic Location

Beginning with the 1996 HSIP, a set of safety warrants was established for intersections and roadway segments to target locations exhibiting a pattern of correctable crash types or conditions, as well as locations with a significant increase in crash frequency during the past calendar year. NCDOT has continued to expand and modify the safety warrants throughout the years to improve the identification process.

NCDOT initially screens the network (including local roads) for potential safety improvement locations using four categories of safety warrants: intersections, sections, bridges, and bicycle and pedestrian intersections. The safety warrants are analyzed annually using 5 to 10 years of crash data by querying the crash database. The current warrant criteria are based on crash frequency, severity, conditions, and percentage of target crashes. When a location meets the warrant criteria, it is flagged. As an example, an interstate segment would be flagged based on run-off road crashes if a minimum of 30 total crashes occurred on the segment, the crash rate is greater than 60 crashes per mile, and a minimum of 60 percent of the total crashes were run off the road. After a location is flagged, a weighting factor is calculated based on the warrant criteria. The weighting factors are summed for locations meeting multiple warrants and are used to rank locations to determine which will receive priority for further analysis and investigation by the corresponding Regional Traffic Engineering and Highway Division staff. The Regional Traffic Engineers are responsible for identifying potential countermeasures and developing projects.

All safety projects are submitted to North Carolina’s Safety Oversight Committee, which was established to help select projects to receive Spot Safety Program funding. To provide clear and consistent data-driven selection process, the Spot Safety Index (SSI) was developed as a decision support tool to perform an initial prioritization of all candidate projects from across the state. It ensures safety investments are focused on locations with the greatest need and potential for improvement. The SSI is calculated based on a 100-point scale and is composed of four parts: Safety Factor (60 points), Constructability (5 points – e.g., ROW acquisition needs), Department Goals (5 points) and Division/Region Priority (30 points). The Safety Factor is based on the benefit-cost ratio, Severity Index, and whether the project is identified in the HSIP List or identified through a Road Safety Audit (RSA). An initial list of prioritized projects is developed by ranking projects based on the SSI. However, the Committee must take other considerations into account to develop the final list, including distribution of funding to the 14 districts and the effectiveness of countermeasures identified in the projects based on results from the state’s evaluation group.

Key Accomplishments

• Developed network screening method to identify locations with severe and correctable crash patterns.
• Continued to update network screening process to improve the identification of relevant safety issues and locations.
• Developed systematic project prioritization ranking method that considers benefit-cost analysis, departmental and regional priorities, and ease of constructability.

Results

The development of the safety warrants for use in the network screening process has enabled NCDOT to focus their analysis on the identification of locations with severe crashes and crash patterns correctable by infrastructure safety countermeasures. NCDOT also has successfully established a clear and consistent data-driven process for selecting and prioritizing projects for funding.

Contact

Stephen Lowry
Safety Improvement Engineer
North Carolina Department of Transportation
919-773-2892
slowry@ncdot.gov