TECHBRIEF

Research, Development, and 

Technology

Turner-Fairbank Highway 

Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

www.fhwa.dot.gov/research

Safety Evaluation of Multiple 

Strategies at Stop-Controlled 

Intersections

FHWA Publication No.: FHWA-HRT-17-087

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 Stop-Controlled Intersections

(FHWA-HRT-17-086).

Objective

The Federal Highway Administration (FHWA) 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 goal 

of the DCMF program is to save lives by identifying new 

safety strategies that effectively reduce crashes and to 

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 provide technical feedback on 

safety improvements to the DCMF program and implement 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. 
2

This study evaluated a combined application of multiple low-cost treatments at stopcontrolled intersections. Improvements 

included basic signing and pavement markings. The intent of this strategy is to reduce 

the frequency and severity of crashes at 

stop-controlled intersections by alerting drivers to the presence and type of 

approaching intersection.

Many studies have explored the safety 

effectiveness of basic signing or pavement 

marking improvements. 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, agencies have shown 

increased interest in the widespread 

installations 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 stop-controlled and 

signalized intersections statewide. Typical 

low-cost treatments at stop-controlled intersections in South Carolina included signing and pavement marking improvements. 

Each intersection received all treatments 

appropriate for the site.

The following is an overview of the types 

of basic signing and pavement marking improvements. Each treatment was 

installed when appropriate. Each intersection received a unique package of improvements suited for implementation at that 

site. The possible improvements included 

the following:

• Signing improvements:

o Double up 36-inch x 36-inch intersection warning signs on fluorescent 

yellow sheeting on the left and right 

sides of the street.

o Add an advance street name plaque 

(W16-8) on fluorescent yellow sheeting accompanying each right-side 

intersection warning sign.

o Double up 48-inch x 48-inch STOP 

and YIELD signs on the left and 

right sides.

o Use retroreflective sign posts for the 

above signs.

• Pavement marking improvements:

o Place stop lines within 4 to 10 ft of 

the nearest through lane along the 

major road.

o Install yield lines at all lanes having 

yield conditions.

o Add a dashed white edge line 

through the intersection along the 

major road.

o Re-mark all existing stop lines, crosswalks, arrows, and word messages 

unless:

■ The roadway has been resurfaced 

within 1 calendar year and new 

thermoplastic markings have been 

applied.

■ Existing markings are uniformly 

reflective and aboveground thickness is 90 mil or greater.
3

■ Otherwise directed by a district 

representative.

o Mark all turn lanes to include the pattern of lane arrows and accompanying word message “ONLY” based on 

the turn lane length, in accordance 

with Standard Drawing 625-410-00.

A literature search focused on the safety 

effects of the specific strategies at stopcontrolled intersections. Very few studies 

investigated the effects of multiple 

strategies. An evaluation by the Institute 

of Transportation Engineers, which 

examined the safety effects of doubling 

up stop signs, found that these strategies 

yielded an 11-percent reduction in total 

crashes.(1) An FHWA study found that 

doubling up and oversizing stop signs 

resulted in a 48-percent reduction in total 

crashes; however, there were potential 

biases with study design, sample size, 

and selection bias.(2) Multiple studies 

confirm the conspicuity of fluorescent 

sign sheeting.(3,4) 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.(5) Several studies 

evaluated the installation of minor-road 

stop line pavement markings, resulting 

in a total crash reduction of 19 percent in 

two studies and a 47-percent reduction in 

right-angle crashes in one of the studies.(1,6)

The combination of adding a center line, 

adding a stop line, and replacing a 24-inch 

stop sign with a 30-inch stop sign yielded 

a 67-percent reduction in right-angle 

crashes.(7) The combination of stop lines 

and short intervals of double yellow center 

lines through the intersection resulted in a 

53-percent decrease in total crashes.(2)

Most of these studies employed study 

designs that lacked statistical rigor and 

frequently neglected to estimate standard 

errors for the crash reductions, which 

makes it difficult to put much credence in 

the results. Furthermore, none of the 

previous studies conducted a comprehensive evaluation with regard to crash type 

and severity. The previous studies generally 

reported the effect on total crashes or angle 

crashes, and virtually none estimated the 

effect on injury crashes. Thus, there is a 

need for additional research of the stopcontrolled strategies of interest that 

employs rigorous study designs and 

analyzes a full range of crash types and 

severities.

Methodology

This study examined the safety impacts of 

multiple low-cost signing and pavement 

marking treatments at stop-controlled intersections in South Carolina on total, fatal and 

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

crash frequency.

The data sample included 434 treatment 

sites and 568 reference sites of all intersection types. The research team categorized 

intersections for evaluation using the following configuration types:

• 3 x 22: Three-legged intersections with 

two lanes on the main line and two 

lanes on the cross street.

• 4 x 22: Four-legged intersections with 

two lanes on the main line and two 

lanes on the cross street.
4

• 3 x 42: Three-legged intersections with 

four lanes on the main line and two 

lanes on the cross street.

• 4 x 42: Four-legged intersections with 

four lanes on the main line and two 

lanes on the cross street.

The evaluation made use of the 

empirical Bayesian (EB) methodology for 

observational before–after studies.(8) 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) was found to have 

the following advantages:

• Overcomes the difficulties of using 

crash rates in normalizing for volume 

differences between the before and 

after periods.

• Accounts for time trends.

• Reduces the level of uncertainty in the 

estimates of safety effect.

• Properly accounts for differences in 

crash experience and reporting practice 

in amalgamating data and results from 

diverse jurisdictions.

• Provides a foundation for developing 

guidelines for estimating the likely

safety consequences of a contemplated 

strategy.

The researchers estimated the SPFs 

used in the EB methodology through 

generalized linear modeling assuming a 

negative binomial error distribution, which 

is consistent with the state of research 

in developing these models. In specifying 

a negative binomial error structure, 

the researchers 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 the development of SPFs, including a description of 

how the estimate of safety effects for target 

crashes was 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 shows the aggregate results. For all 

crash types, the table provides the estimates 

of expected crashes in the after period 

without treatment, the observed crashes 

in the after period, the estimated crash 

modification factor (CMF), and the standard 

error of the CMF.

The reductions were statistically significant 

at the 95-percent confidence level for all 

crash types. For all crash types combined, 

the CMFs were 0.917 for all severities and 

0.899 for fatal and injury crashes. The crash 

type with the smallest CMF, which indicates 

the greatest crash reduction, was nighttime 

crashes with a CMF of 0.853. The CMFs for 

rear-end and right-angle crashes were 0.933 

and 0.941, respectively. 
5

Disaggregate Analysis

The disaggregate analysis identified those 

conditions under which the multiple lowcost treatments are more effective. The 

research team identified several variables 

of interest, including area type, number of 

legs, lane configuration of the main line 

and cross street, traffic volumes, and 

expected crashes without treatment. All of 

these variables are likely correlated, and 

caution should be exercised in interpreting 

and applying the disaggregate analysis 

results.

The disaggregate analysis indicated larger 

crash reductions of all types for rural areas, 

four-legged intersections, and intersections 

with two-lane major roads. For total 

entering volume and expected crashes 

before treatment, the disaggregate analysis 

indicated the strategy is more effective on 

average for intersections with lower traffic 

volumes and fewer expected crashes per 

year. However, as noted above, this effect 

may be due to other correlated variables.

Economic Analysis

The research team conducted an economic 

analysis to estimate the B/C ratio for implementing various low-cost pavement marking and signing improvements at stopcontrolled intersections. The research team 

used the statistically significant aggregate 

reduction in total crashes to calculate the 

conservative value of benefits for an average intersection.

Based on work order cost data for more 

than 800 unsignalized intersections provided by SCDOT, the economic analysis 

assumed an average total construction cost 

of $5,900. 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. In addition, annual 

maintenance and operations costs were not 

available but were assumed to be zero (i.e., 

Crash Type

After-Period Crashes— 

Expected (Without 

Systemic Improvement) 

After-Period Crashes— 

Observed 

Estimated 

CMF

Standard Error of 

Estimated CMF

Total 4,614 4,231 0.917* 0.017

Fatal and injury 1,434 1,290 0.899* 0.028

Rear-end 1,577 1,472 0.933* 0.030

Right-angle 1,955 1,840 0.941* 0.026

Nighttime 1,072 953 0.853* 0.031

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

*Indicates CMF estimates statistically significant at the 95-percent confidence level.
6

these costs will not be incurred within the 

service life).

The analysis assumed the useful service 

life for safety benefits was approximately 

7 years. Pavement markings were assumed 

to last roughly 7 years and signs roughly 

10 years, for an approximate average of 

7 years for the overall project. A conservative analysis using a service life of 3 years 

was also conducted. 

Using comprehensive crash cost estimates 

for fatal, injury, and property-damageonly crashes and the severity distribution 

at treatment sites, the research team 

estimated the cost for an average crash at 

a stop-controlled intersection and updated 

this value to 2015 U.S. dollars (USD) at 

the time of analysis using the value of a 

statistical life provided in a 2015 USDOT 

memorandum. The team applied the ratio 

of the 2015 value of $9.4 million to the 2001 

value of $3.8 million, yielding an average 

cost of $132,071 in 2015 USD.(9,10) 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.(10)

The research team calculated total crash 

reduction 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 119.7 crashes 

per year for the sample sites, or an average 

reduction of 0.3 crashes per site per year 

across the 434 treatment sites. Similarly, 

the treatments reduced fatal and injury 

crashes by 45 crashes per year across the 

sample sites, or an average reduction of 

0.1 fatal and injury crashes reduced per site 

per year.

To calculate the annual economic benefits, the research team multiplied 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.

These results suggest that the unsignalized intersection treatments, even with conservative assumptions of service life and 

the value of a statistical life, can be cost 

effective in reducing total crashes at stopcontrolled intersections.

Summary and Conclusions

This study was a rigorous before–after 

evaluation of the safety effectiveness, as 

measured by crash frequency, of systemic 

low-cost improvements at stop-controlled 

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 

Service

Life

Lower 

Bound

Average 

B/C

Upper

Bound

3 years 7.1 12.4 17.5

7 years 14.5 25.5 35.9

Table 2. B/C ratios.
7

multiple low-cost treatments are most 

effective. Variables of interest included area 

type, number of legs, lane configuration of 

the main line and the cross street, traffic

volumes, and expected crashes without 

treatment. The disaggregate analysis 

indicated larger crash reductions of 

all types for rural areas, four-legged 

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

and expected crashes before treatment, 

the disaggregate analysis indicated the 

strategy is more effective on average for 

intersections with lower traffic volumes and 

fewer expected crashes per year. However, 

it is important to be cautious in interpreting 

and applying these disaggregate analysis 

results, which are likely confounded by 

multiple correlative effects.

The B/C ratio, estimated with conservative 

cost and service life assumptions and 

considering the benefits for total crashes, 

is 12.4:1. With the USDOT recommended 

sensitivity analysis, these values could 

range from 7.1:1 up to 17.5:1. 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 stop-controlled 

intersections.

References

1. Institute of Transportation Engineers. 

(2004). Toolbox of Countermeasures 

and Their Potential Effectiveness to 

Make Intersections Safer, Briefing Sheet 

8, ITE, FHWA, Washington, DC.

2. Federal Highway Administration. (2009). 

Stop Sign-Controlled Intersections: 

Enhanced Signs and Markings, Report 

No. FHWA-SA-09-010, Federal Highway 

Administration, Washington, DC.

3. 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.

4. 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, pp. 185–203.

5. Virginia Department of Transportation. 

(2008). Evaluation of Retroreflective 

Material on Stop Sign Posts in Virginia,

Virginia Department of Transportation, 

Richmond, VA. Available online: 

http://www.virginiadot.org/projects/

resources/4_09_Retroreflective_

Material_Final_Report.pdf, last accessed 

July 9, 2011.

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

CMF 0.917 0.899 0.933 0.941 0.853

Standard error 0.017 0.028 0.030 0.026 0.031

Table 3. Recommended CMFs.
8

DECEMBER 2017 FHWA-HRT-17-087

HRDI-20/12-17(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—Stop-controlled intersection, signing, pavement marking, 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 they are considered essential to the objective of the document.

Quality Assurance Statement—The Federal Highway Administration (FHWA) provides 

high-quality information to serve the Government, industry, and public in a manner that 

promotes public understanding. Standards and policies are used to ensure and maximize the 

quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality 

issues and adjusts its programs and processes to ensure continuous quality improvement.

6. Golembiewski, G.A. and Chandler, B. 

(2008). Intersection Safety: A Manual 

for Local Rural Road Owners, Report 

No. FHWA-SA-11-08, Federal Highway 

Administration, Washington, DC.

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

Improvements,” The Traffic Safety 

Toolbox: A Primer on Traffic Safety,

pp. 265–272, Institute of Transportation 

Engineers, Washington, DC.

8. 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. 

9. 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, McLean, VA. 

10. U.S. Department of Transportation. 

(2015). Guidance on Treatment of 

the Economic Value of a Statistical 

Life (VSL) in U.S. Department of 

Transportation Analyses—2015 Adjustment, Memorandum, U.S. Department 

of Transportation, Office of the Secretary of Transportation, Washington, 

DC. Available online: https://cms.dot.

gov/sites/dot.gov/files/docs/VSL2015_0.

pdf, last accessed March 29, 2016.