FHWA-SA-09-011

This case study is one in a series documenting successful 

intersection safety treatments and the crash reductions that 

were experienced. Traffic engineers and other transportation 

professionals can use the information contained in the case 

study to answer the following questions:

•	 What isasimpleinexpensivetreatment toreducecrashesat signalized

intersections in urban areas thatoccurduetoreducedvisibility?

•	 How manycrashesdidthis treatment reduce?

•	 Arethereanyimplementation issuesassociated with this treatment,

andif so, how can theybeovercome?

Retroreflective Borders on 

Traffic Signal Backplates

A South Carolina Success Story

Photo courtesy of KLS (used with permission).

Intersection Safety Case Study
Photo courtesy of KLS (used with permission).

2 FHWA | Retroreflective Borders on Traffic Signal Backplates

Introduction

Red-light running is one of the most serious traffic problems that Americans face today. It is 

estimated that vehicles running red lights cause more than 200,000 crashes, 170,000 injuries 

and approximately 900 deaths per year1

. Some of these crashes occur because drivers are 

unaware of the presence of an intersection or are unable to see the traffic control device in 

time to comply.

The use of retroreflective borders on existing signal backplates to increase the visibility of 

traffic signals (particularly at night or under low-visibility conditions) is a simple, inexpensive 

countermeasure that can reduce crashes by improving driver awareness of traffic signals2

.

“Since the addition of 

retroreflective borders at three 

test locations in Columbia, an 

overall reduction in total crashes 

was found. The South Carolina 

Department of Transportation 

hopes to continue to use 

retroreflective borders as a low 

cost safety improvement tool 

when appropriate.”

Joey Riddle 

South Carolina Department of 

Transportation 

Objective

The following case study showcases a successful and effective low-cost treatment that measurably improved 

safety at three signalized intersections in Columbia, South Carolina (SC). The treatment consisted of adding a 

retroreflective border to the existing signal backplates.

1 Federal Highway Administration Office of Safety Red-Light Running web site (http://safety.fhwa.dot.gov/intersection/redlight).

Figure 1: Retroreflective backplate border 

Signal backplate

Retroreflective 

Border applied 

to perimeter of 

backplate
Photos courtesy of South Carolina Department of Transportation (used with permission).

FHWA | Retroreflective Borders on Traffic Signal Backplates

3

Treatment Summary

All intersection examples used in this report are from Columbia, SC. Existing intersection treatments met minimum 

Manual on Uniform Traffic Control Devices (MUTCD) standards. 

This case study examines the application of a three-inch, yellow retroreflective border to existing signal backplates 

(framing the signal head) at three intersections. The border was visible during the day, but its visibility increased 

significantly at night and under limited visibility conditions (as shown in Figure 2). In addition, retroreflective 

borders added to signal backplates can help road users to more readily detect the presence of a signalized 

intersection during power outages.

Figure 2: Retroreflective backplate borders

Evaluation Methodology

This case study examines three signalized 

intersections in Columbia, SC, with a high incidence 

of crashes due to driver violation of the traffic signals. 

Crash reduction results were based on a review of 

“before and after” data from these intersections 

during 54 -month periods, between 2003—20073. 

(The “before” and “after” observation periods ranged 

from 25 - 29 months). 

2 The Manual of Uniform Traffic Control Devices (MUTCD) allows the optional use of signal backplates, stating that a signal backplate is “a thin strip of material that 

extends outward from and parallel to a signal face on all sides of a signal housing to provide a background for improved visibility of the signal indications” (Section 

4A.02 Definitions Relating to Highway Traffic Signals of the 2003 MUTCD). While the use of only the backplates does increase the contrast between the signal head and 

its background, backplates are only effective in lighted conditions for increasing the signal head’s visual target size and for providing contrast against backgrounds such 

as trees, sky, clouds, and, especially, sun. (Section 4D.17, Visibility, Shielding, and Positioning of Signal Faces of the 2003 MUTCD). 

3 Note that crash reduction averages in this report reflect the percent reduction per year based on the difference between the total number of “before” and “after” crashes. 

Only crashes occurring within 250 feet of the intersections were considered.
4 FHWA | Retroreflective Borders on Traffic Signal Backplates

Results

Problem: Drivers were violating traffic signals at three signalized intersections due to low visibility, leading to a high 

number of crashes at these intersections.

Solution: The South Carolina Department of Transportation (SCDOT) installed yellow retroreflective borders around 

the perimeter of the face of existing signal backplates at selected signalized intersections in June, 2005. 

Table 1: Summarizes the “before and after” crash analysis at the treated intersections Following the table is a brief 

discussion of the results at each intersection.

Table 1: Summary of “Before” and “After” Results at the Treated Intersections.

Locations

Months

Implementation 

Date

Total CrashesInjury CrashesLate-night/Earlymorning Crashes

Months

Total CrashesInjury CrashesLate-night/Earlymorning Crashes

Sumter Highway 

(US 378) with Lower 

Richland Boulevard 

(S-37)

I-26 Westbound 

(WB) with Piney 

Grove Road 

(S-1280)

Piney Grove 

Road (S-1280) 

with Jamil Road 

(S-1791)

TOTAL 87 65 22 23 75 40 12 10 28.6% 36.7% 49.6% Total Crashes Injury Crashes Late-night/Early- morning Crashes

Percent Reduction 

In Crashes/Year Before After

29

29

29

33

13

19

17

5

0

7

8

8

25

25

25

21

9

10

10

1

1

6

1

3

26.2%

19.7%

38.9%

31.8%

76.8%

NA

0.6%

85.5%

56.5%

June-05

June-05

June-05
FHWA | Retroreflective Borders on Traffic Signal Backplates

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Sumter Highway (US 378) with Lower 

Richland Boulevard (S-37)

Sumter Highway (US 378) has three lanes in each 

direction; while Lower Richland Boulevard (S-37) consists 

of a single lane in each direction, with an additional 

right-turn lane at US 378. Both roadways have a speed 

limit of 45 mph. Average daily traffic (ADT) at this 

intersection decreased from 37,900 in the “before” period 

to 35,725 in the “after” period4. Retroreflective borders 

were installed only on signal backplates on Sumter 

Highway (US 378). 

The treatment resulted in an average crash reduction of 

26.2 percent and reduced injury crashes by 31.8 percent 

per year at this intersection. The total number of latenight/early-morning crashes remained relatively stable.

I-26 Westbound (WB) with Piney 

Grove Road (S-1280)

The I-26 WB on-ramp has two lanes, while the off-ramp 

has three lanes (one left-turn only, one shared left/

through lane, and one right-turn only). Piney Grove Road 

(S-1280) has a speed limit of 40 mph, with two through 

lanes and a separate left-turn lane in each direction. 

Intersection ADT was 29,480 for both the “before” and 

“after” periods. Retroreflective borders were installed only 

on Piney Grove Road (S-1280).

The treatment resulted in an average crash reduction of 

19.7 percent, reduced injury crashes by 76.8 percent per 

year and reduced late-night/early-morning crashes by 

85.5 percent per year at this intersection.

Piney Grove Road (S-1280) with 

Jamil Road (S-1791)

Piney Grove Road (S-1280) has a speed limit of 40 mph 

with two through lanes and a separate left-turn lane 

in each direction. Jamil Road (S-1791) has a 35 mph 

speed limit with a single through lane and a separate 

left-turn lane in each direction. Intersection ADT 

was 35,940 for both the “before” and “after” periods. 

Retroreflective borders were installed only on Piney 

Grove Road (S-1280). 

This intersection experienced the largest drop in total 

crashes—The treatment resulted in an average crash 

reduction of 38.9 percent and reduced late-night/

early-morning crashes by 56.5 percent per year. Injury 

crashes increased slightly from zero in the before 

period to one in the after period. 

4 Note that crash reduction averages in this report reflect the percent reduction per year based on the difference between the total number of “before” and “after” crashes.
Photo courtesy of KLS (used with permission).

6 FHWA | Retroreflective Borders on Traffic Signal Backplates

Figure 3: Retroreflective borders installed on signal backplates

Discussion

Implementation Issues

SCDOT experienced no implementation issues with 

this countermeasure. However, if a traffic signal is not 

equipped with a backplate, implementation plans 

will need to account for the addition of backplates, 

as well as an increase in needed support strength to 

accommodate the backplate load on the mast arm 

or cable. 

Cost

The costs for implementing the countermeasure 

were approximately $1,500 per intersection5.

Time Frame

The installation of the retroreflective border on 

existing signal backplates at each intersection was 

completed within two hours. 

Effectiveness 

The addition of a retroreflective border (as shown in 

Figure 3) to existing signal backplates was effective 

in reducing overall crashes at these signalized 

intersections. SCDOT attributes their success to 

targeting appropriate intersection approaches that 

would benefit from this enhanced treatment—

specifically, intersections where conditions allow an 

approaching driver to see the enhanced traffic signal 

at a distance, in time to respond. Further, SCDOT is in 

the process of implementing a district wide (District 

One) program to install retroreflective borders at other 

signalized intersections.

Summary of Results

The “before” treatments at all three intersections met 

minimum MUTCD standards. The safety enhancement 

discussed in this study increased the visibility of the traffic 

signal and reduced crashes. The three intersections 

combined experienced a 28.6 percent reduction in 

total crashes, 36.7 percent reduction in injury crashes, 

and 49.6 percent reduction in late-night/earlymorning crashes after the installation. The average 

reductions in crashes achieved by the treatments exceed 

the expected crash reductions for adding retroreflective 

borders to signal backplates in urban areas of 15 percent 

mentioned in the Desktop Reference for Crash Reduction 

Factors (September 2007), published by the United States 

Department of Transportation (USDOT) FHWA[1].

5 Cost estimate does not include costs of the signal backplate.
FHWA | Retroreflective Borders on Traffic Signal Backplates

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References

1) Desktop Reference for Crash Reduction Factors, FHWASA-07-015, USDOT FHWA September 2007.

2) Senior Mobility Series: Article 4: Marking the Way to 

Greater Safety by Gene Amparano and David A. Morena 

FHWA July/August 2006 · Vol. 70 · No. 1.

3) MUTCD - Interim Approval for Use of Retroreflective 

Borders on Signal Backplates, Regina S. McElroy, Director, 

Office of Transportation Operations. February 6, 2004; 

(can be accessed at http://mutcd.fhwa.dot.gov/

res-interim_approvals.htm).

4) Miska, E., P. de Leur, and T. Sayed. “Road Safety 

Performance Associated with Improved Traffic Signal 

Design and Increased Signal Conspicuity.” ITE, 72nd Annual 

meeting, Philadelphia, PA. Washington, DC, 2002.

5) Sayed, T., Abdelwahab, W., and Nepomuceno, J., 

“Safety Evaluation of Alternative Signal Head Designs,” 

Transportation Research Record, Transportation Research 

Board, Vol. 1635, pp. 140-146, 1998.
FHWA-SA-09-011 February 2010

For More Information

Ed Rice

Intersection Safety Team Leader, 

FHWA Office of Safety

202.366.9064

ed.rice@dot.gov

Joey D. Riddle

SCDOT Traffic Safety and Systems

803.737.3582

RiddleJD@dot.state.sc.us

Visit FHWA’s intersection safety web site to download this and 

other case studies highlighting proven intersection safety 

treatments from across the country:

http://safety.fhwa.dot.gov/intersection