TECHBRIEF Safety Evaluation of 

Multiple Strategies at

Signalized Intersections

FHWA Publication No.: FHWA-HRT-17-063

FHWA Contact: Roya Amjadi, HRDS-20, (202) 493-3383, 

roya.amjadi@dot.gov

This document is a technical summary of the Federal 

Highway Administration report Safety Evaluation 

of Multiple Strategies at Signalized Intersections 

(FHWA-HRT-17-062).

Objective

The Federal Highway Administration established the 

Development of Crash Modification Factors (DCMF) program in 2012 to address highway safety research needs for 

evaluating new and innovative safety strategies (improvements) by developing reliable quantitative estimates of 

their effectiveness in reducing crashes. The ultimate goal 

of the DCMF program is to save lives by identifying new 

safety strategies that effectively reduce crashes and 

promote those strategies for nationwide implementation 

by providing measures of their safety effectiveness and 

benefit-cost (B/C) ratios through research. State transportation departments and other transportation agencies 

need to have objective measures for safety effectiveness 

and B/C ratios before investing in broad applications 

of new strategies for safety improvements. Forty State

transportation departments have provided technical 

feedback on safety improvements to the DCMF program 

and implemented new safety improvements to facilitate 

evaluations. These States are members of the Evaluation 

of Low-Cost Safety Improvements Pooled Fund Study, 

which functions under the DCMF program. 

This study evaluated multiple low-cost treatments at 

signalized intersections. Improvements included basic 

signing, pavement marking, and signal enhancements. 

This strategy is intended to reduce the frequency and 

Research, Development, and 

Technology

Turner-Fairbank Highway 

Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

www.fhwa.dot.gov/research
2

severity of crashes at signalized intersections by alerting drivers to the presence, 

type, and configuration of the approaching 

intersection. 

Many studies have explored the safety 

effectiveness of some of the individual 

countermeasures. However, no study has 

conducted a rigorous evaluation of the 

effectiveness of installing packages of these 

strategies in combination across many 

intersections. This study sought to fill this 

knowledge gap.

Introduction

In recent years, there has been an increased 

interest in the widespread installation of 

low-cost safety treatments throughout 

an entire jurisdiction. The South Carolina 

Department of Transportation (SCDOT) 

embraced this approach in its intersection 

safety improvement plan and identified 

a number of low-cost strategies for 

implementation at signalized intersections 

statewide. Typical low-cost treatments at 

signalized intersections in South Carolina 

included improvements to basic signing, 

pavement markings, and traffic signals. 

South Carolina selected a unique package of intersection improvements for each 

intersection. No treatment packages were 

installed at all intersections, and each treatment was only considered for installation 

where appropriate. The following is a list of 

the individual improvements installed as 

part of the packages at the signalized intersections in South Carolina: 

• Replace all signal heads.

• Replace pedestrian signal heads, 

pushbuttons, and signs.

• Install backplates with retroreflective 

borders on all signal heads.

• Re-stripe stop lines.

• Re-stripe crosswalks.

• Install warning signs.

• Install overhead signs (e.g., R10-12, 

R3-5L, and R3-5R).

• Install curb ramps.

A literature search focused on the safety 

effects of the specific strategies at signalized 

intersections. The project team identified 

very few studies that investigated the 

combined effects of multiple strategies. One 

study determined the installation of advance 

warning signs at signalized intersections 

resulted in a 35-percent reduction in 

right-angle crashes.(1) Multiple studies 

confirmed the conspicuity of fluorescent 

sign sheeting.(2,3) A Virginia Department of 

Transportation study used a video survey 

to link retroreflective sign posts with 

improved nighttime visibility in comparison 

to signs without retroreflective material on 

the posts.(4) Several studies evaluated the 

installation of retroreflective backplates. One 

resulted in crash reductions of 20 percent in 

total crashes, 44 percent in angle crashes, 

and 10 percent in rear-end crashes.(5)

Another yielded a 29-percent reduction 

in total crashes, 37-percent reduction in 

injury crashes, and 50-percent reduction 

in late-night/early-morning crashes.(6) 

The combination of adding retroreflective 

backplates with upgraded signal lenses 

reduced total crashes by 9 percent, severe 

crashes by 10 percent, and nighttime 

crashes by 14 percent.(7) A number of 

studies evaluated the safety effects of using 

12-inch or larger signal lenses, and resulted
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in reductions in total, injury, angle, and 

nighttime crashes.(8–10)

Most of these studies employed study 

designs that lacked statistical rigor, had 

limited sample sizes, or had sites in limited 

geographic areas, which made it difficult 

to put much credence in the results. 

Furthermore, no prior studies involved a 

combination of as many countermeasures 

used in this research. Thus, additional 

research is warranted that is based on a 

more rigorous analysis of these treatments, 

especially research that considers the 

effects of multiple low-cost strategies 

implemented in combination.

Methodology

This study examined the safety impacts 

of multiple low-cost signing, pavement 

marking, and traffic signal treatments at 

signalized intersections in South Carolina 

on total, fatal and injury, rear-end, rightangle, and nighttime crash frequencies.

The data set included 84 treatment sites and 

368 reference sites of all intersection types. 

The project team categorized intersections 

for evaluation using the following 

configuration types:

• 3x22: Three-legged intersections with 

two lanes on the mainline and two 

lanes on the cross street.

• 4x22: Four-legged intersections with 

two lanes on the mainline and two 

lanes on the cross street.

• 3x42: Three-legged intersections with 

four lanes on the mainline and two 

lanes on the cross street.

• 4x42: Four-legged intersections with 

four lanes on the mainline and two 

lanes on the cross street.

The evaluation made use of the empirical 

Bayes (EB) methodology for observational 

before-after studies.(11) This methodology is 

considered rigorous in that it accounts for 

regression-to-the-mean using a reference 

group of similar but untreated sites. 

In the process, the use of safety performance 

functions (SPFs) addressed the following:

• Overcoming the difficulties of using 

crash rates in normalizing for volume 

differences between the before and 

after periods.

• Accounting for time trends (in the form 

of before-after adjustment factors, not 

yearly indicator variables).

• Reducing the level of uncertainty in the 

estimates of safety effects.

• Properly accounting for differences in 

crash experience and reporting practice 

in amalgamating data and results from 

diverse jurisdictions.

• Providing a foundation for developing guidelines for estimating the likely 

safety consequences of a contemplated strategy.

The project team estimated the SPFs 

used in the EB methodology through 

generalized linear modeling assuming a 

negative binomial error distribution, which 

was consistent with the state of research 

in developing these models. In specifying 

a negative binomial error structure, 

the project team estimated a constant 

overdispersion parameter from the model 

and the data. For a given dataset, smaller 

values of this parameter indicate relatively 

better models.

The full report includes a detailed 

explanation of the methodology and 
4

the development of SPFs, including a 

description of how the estimates of safety 

effects for target crashes were calculated.

Results

This brief presents the research results in 

two parts. The first part contains aggregate 

results. The second part is based on a disaggregate analysis that sought to identify the 

optimal conditions for installation of the 

treatment.

Aggregate Analysis

Table 1 provides the estimates of expected 

crashes in the after period without 

treatment, the observed crashes in the after 

period, and the estimated crash modification 

factor (CMF) and its standard error for each 

crash type considered in this study. The 

results in table 1 indicate reductions for 

all crash types analyzed in this study. The 

CMFs for fatal and injury and right-angle 

crashes are 0.893 and 0.883, respectively, 

which are statistically significant at the 

95-percent confidence level. The CMFs for 

total, rear-end, and nighttime crashes are 

0.955, 0.974, and 0.969, respectively. The 

CMFs for total, rear-end, and nighttime 

crashes are not statistically significant at the 

95-percent confidence level, but the CMF 

for total crashes is statistically significant at 

the 90-percent confidence level.

Disaggregate Analysis

The disaggregate analysis identified 

specific CMFs by crash types and different 

conditions and those conditions under 

which the multiple low-cost treatments 

were more effective. The research team 

identified several variables of interest, 

including area type, number of legs, lane 

configuration of the mainline and the cross 

street, and traffic volumes.

The disaggregate analysis indicated larger 

crash reductions of all types for urban 

areas and intersections with two-lane 

major roads. For total entering volume, the 

disaggregate analysis indicated the strategy is slightly more effective on average 

for intersections with lower traffic volumes. 

The disaggregate analysis also showed the 

multi-treatment strategy can yield similar crash reductions across the range of 

expected crashes without the treatments. 

Statistic Total Fatal and Injury Rear-End Right-Angle Nighttime

EB estimate of crashes 

expected in the after 

period without the 

systemic improvement

2,801 617 1,385 1,042 599

Count of crashes observed 

in the after period 2,675 551 1,349 921 581

Estimated CMF 0.955 0.893* 0.974 0.883* 0.969

Standard error of the 

estimated CMF 0.023 0.045 0.034 0.035 0.048

Table 1. Aggregate results for EB before-after study.

*Indicates statistically significant results at the 95-percent confidence level.
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Economic Analysis

An economic analysis was conducted to 

estimate the B/C ratio for implementing 

various pavement marking, signing, signal, 

and pedestrian improvements at signalized 

intersections. The statistically significant 

aggregate reduction in total crashes was 

used to calculate the conservative value of 

benefits for an average intersection.

Based on work order cost data for signalized 

intersections provided by SCDOT, the 

economic analysis assumed an average 

pavement marking and signing construction 

cost of approximately $7,000. Typical cost 

estimates for replacing signal heads, 

installing pedestrian signal assemblies, and 

installing curb ramps were available and 

were roughly $13,300, $18,300, and $10,000 

per intersection, respectively. Preliminary 

engineering, project management, and other 

general costs were not provided; however, 

analysts with this information can split these 

costs between all intersections. SCDOT 

used contractors to select and construct 

treatments at each intersection, and State 

forces planned and managed the project. 

Annual maintenance and operations costs 

were not available except for pedestrian 

signal head maintenance and are otherwise 

assumed to be zero (i.e., these costs will not 

be incurred within the service life).

The analysis assumed the useful service life 

for safety benefits was 7 years. Pavement 

markings were assumed to last roughly 

4 years and all other treatments roughly 

7 to 10 years with minimal maintenance. 

A conservative average of 7 years was used 

for the overall project. 

This study used comprehensive crash cost 

estimates for fatal and injury crashes and 

property-damage-only crashes from the 

recent report by Persaud (updated from an 

earlier report by Council et al.) to estimate 

the annual economic benefits.(9,10) Using 

these numbers and the severity distribution 

at treatment sites, the research team 

estimated the cost for an average crash 

at a signalized intersection as $95,186 in 

2015 dollars.

Persaud refers to a June 2013 U.S. 

Department of Transportation (USDOT) 

memo that prescribes sensitivity analysis 

based on low and high values of crash 

costs.(9,11) Specifically, the USDOT memo 

suggests that analysts should apply sensitivity analysis by estimating B/C ratios for 

0.57 and 1.41 times the 2015 crash costs.(11)

The total crash reduction was calculated 

by subtracting the actual crashes in the 

after period from the expected crashes 

in the after period had the intersection 

treatments not been implemented. The total 

crash reduction was then divided by the 

average number of after period years per 

site to compute the total crashes saved per 

year. The treatments saved 50.6 crashes 

per year for the study sites, or an average 

reduction of 0.6 crashes per site per year 

across the 84 treatment sites. Similarly, 

the treatments resulted in a reduction of 

26.5 fatal and injury crashes, or 

approximately 0.3 fatal and injury crashes 

reduced per site per year across all 

84 sites.

The annual economic benefits were calculated by multiplying the crash reduction per 

site per year by the cost of a crash. Table 2 

presents the resulting B/C ratios, with 

lower and upper bounds resulting from 

the sensitivity analysis for two scenarios: 

1) assuming signing, marking, and signal 

improvements, and 2) assuming scenario 

one plus pedestrian-related improvements.
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These results suggest that the various 

intersection treatments, even with 

conservative assumptions of service life 

and the value of a statistical life, can be cost 

effective in reducing crashes at signalized 

intersections.

Summary and Conclusions

The objective of this study was to undertake a 

rigorous before-after evaluation of the safety 

effectiveness, as measured by crash frequency, of multi-strategy, low-cost improvements at signalized intersections. The study 

used data from South Carolina to examine 

the effects for the specific crash types total, 

fatal and injury, rear-end, right-angle, and 

nighttime crashes. Based on the aggregate 

results, table 3 presents the recommended 

CMFs for the various crash types. 

The disaggregate analysis sought to identify

those conditions under which the multiple 

low-cost treatments are most effective. 

Variables of interest included area type 

(urban or rural), number of legs (three or 

four), lane configuration of the mainline 

and the cross street, traffic volumes, and 

expected crashes without treatment. The 

disaggregate analysis results indicate 

larger crash reductions of all types for 

urban areas and intersections with twolane major roads. For total entering volume, 

the disaggregate analysis results indicate 

the strategy is slightly more effective on 

average for intersections with lower traffic 

volumes. The strategy is approximately 

equally effective across the range of 

expected crashes before treatment.

The B/C ratio, estimated with conservative 

cost and service life assumptions and 

considering the benefits for total crashes, 

is 11.7 to 1 excluding pedestrian improvements. With the USDOT recommended 

sensitivity analysis, these values could 

range from 6.6 to 1 up to 16.4 to 1. These 

results suggest that the multiple lowcost treatments, even with conservative 

assumptions on cost, service life, and the 

value of a statistical life, can be cost effective in 

reducing crashes at signalized intersections.

Treatments Lower Bound Average B/C Upper Bound

Signing, marking, and signal head 

replacements 6.6 11.7 16.4

Signing, marking, signal head 

replacements, and pedestrian signal 

installation with curb ramps

2.3 4.1 5.8

Table 2. B/C ratios. 

Variable Total Fatal and Injury Rear-End Right-Angle Nighttime

CMF 0.955 0.893* 0.974 0.883* 0.969

Standard error 0.023 0.045 0.034 0.035 0.048

Table 3. Recommended CMFs.

*Indicates statistically significant results at the 95-percent confidence level.
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References

1. Polanis, S.F. (1999). “Low-Cost Safety 

Improvements,” The Traffic Safety 

Toolbox: A Primer on Traffic Safety, 

Institute of Transportation Engineers, 

Washington, DC, p. 265–272.

2. Jenssen, G.D., Moen, J., Brekke, B., 

Augdal, A., and Sjohaug, K. (1996). 

Visual Performance of Fluorescent 

Retroreflective Traffic Control Devices, 

Part 1: Human Factors Visibility Study, 

Report No. STF22 A96606, Sintef 

Transport Engineering, Trondheim, 

Norway.

3. Burns, D.M. and Johnson, N.L. (1997). 

The Correlation of Measured Spectral 

Radiance of Fluorescent and Nonfluorescent Materials to Perceived 

Conspicuity under Natural Lighting, DIE 

FARBE 43, Heft 4-6.

4. Virginia Department of Transportation. 

(2008). Evaluation of Retroreflective 

Material on Stop Sign Posts in Virginia, 

Virginia Department of Transportation, 

Richmond, VA. Available at: http://

www.virginiadot.org/vtrc/main/online_

reports/pdf/09-r23.pdf. Last accessed on 

July 9, 2011.

5. Agent, K.R. (2008). Low-Cost Safety 

Measures at Signalized Intersections, 

Report No. KTC-08-11, Kentucky Transportation Center, Lexington, KY.

6. Federal Highway Administration. (2009). 

Retroreflective Borders on Traffic Signal 

Backplates: A South Carolina Success 

Story, Report No FHWA-SA-09-011, 

Federal Highway Administration, 

Washington, DC. 2009. Available 

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

resources/casestudies/fhwasa09011/. 

Last accessed on August 6, 2011.

7. Sayed, T., El Esawy, M., and Pump, J. 

(2007). “Evaluating the Safety Impacts 

of Improving Signal Visibility at Urban 

Signalized Intersections,” 2007 TRB 

86th Annual Meeting: Compendium of 

Papers CD-ROM, Paper Number 07-135, 

Washington, DC.

8. Sayed, T., Abdelwahab, W., and 

Nepomuceno, J. (1998). “Safety 

Evaluation of Alternative Signal Head 

Designs,” Journal of the Transportation 

Research Board, 1635, p. 140–146.

9. Federal Highway Administration. (2009). 

Improving Safety by Providing All-Red 

Clearance Intervals and Larger Signal 

Lenses, Report No. FHWA-SA-09-014, 

Federal Highway Administration, 

Washington, DC. Available at: http://

safety.fhwa.dot.gov/intersection/

resources/fhwasa09027/resources/

Technical%20Report%20Providing%20

All-Red%20Clearance%20Intervals.pdf. 

Last accessed August 6, 2011. 

10. Sayed, T., El Esawy, M., and Pump, J. 

(2007). “Evaluating the Safety Impacts 

of Improving Signal Visibility at Urban 

Signalized Intersections,”2007 TRB 

86th Annual Meeting: Compendium of 

Papers CD-ROM, Paper Number 07-135, 

Washington, DC.

11. Hauer, E. (1997). Observational 

Before-After Studies in Road Safety—

Estimating the Effect of Highway and 

Traffic Engineering Measures on Road 

Safety, Elsevier Science, Incorporated,

Amsterdam, The Netherlands.
8

AUGUST 2017 FHWA-HRT-17-063

HRDS-20/08-17(200)E

Researchers—Thanh Le, Frank Gross, Kimberly Eccles, Jonathan Soika, and Bhagwant Persaud.

Distribution—This TechBrief is being distributed according to a standard distribution. Direct 

distribution is being made to the Divisions and Resource Center.

Availability—This TechBrief may be obtained from the FHWA Product Distribution Center by e-mail 

to report.center@dot.gov, fax to (814) 239-2156, phone to (814) 239-1160, or online at http://www.

fhwa.dot.gov/research.

Key Words— Signalized intersection, Signing, Pavement marking, Signal improvements, Pedestrian 

improvements, Low-cost, Safety improvements, Safety evaluations, Empirical Bayesian.

Notice—This document is disseminated under the sponsorship of the U.S. Department of 

Transportation in the interest of information exchange. The U.S. Government assumes no liability 

for the use of the information contained in this document. The U.S. Government does not endorse 

products or manufacturers. Trademarks or manufacturers’ names appear in this report only because 

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Quality Assurance Statement—The Federal Highway Administration (FHWA) provides highquality information to serve the Government, industry, and public in a manner that promotes public 

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programs and processes to ensure continuous quality improvement.

12. Persaud, B. (2014). How to Convert Value 

of a Statistical Life to Cost per Crash by 

Severity, Crash Type, and Speed Limit, 

Draft memo for DCMF Evaluations, 

13. Council, F., Zaloshnja, E., Miller, 

T., and Persaud, B. (2005). Crash 

Cost Estimates by Maximum PoliceReported Injury Severity Within 

Selected Crash Geometries, Report No. 

FHWA-HRT05-051, Federal Highway 

Administration, Washington, DC. 

14. U.S. Department of Transportation. 

(2014). Guidance on Treatment of the 

Economic Value of a Statistical Life (VSL) 

in U.S. Department of Transportation 

Analyses—2014 Adjustment, U.S. 

Department of Transportation, 

Washington, DC. 2014. Available online 

at: http://www.dot.gov/sites/dot.gov/

files/docs/VSL_Guidance_2014.pdf. Last 

accessed on: