TECHBRIEF Safety Evaluation of 

Intersection Conflict 

Warning Systems (ICWS)

FHWA Publication No.: FHWA-HRT-15-076

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

roya.amjadi@fhwa.dot.gov

This document is a technical summary of the forthcoming Federal Highway Administration report Safety 

Evaluation of Intersection Conflict Warning Systems 

(ICWS) (HRT-16-035).

Objective

The Federal Highway Administration (FHWA) organized 

40 States to participate in the FHWA Evaluation of LowCost Safety Improvements Pooled Fund Study (ELCSI-PFS) 

as part of its strategic highway safety plan support effort. 

The goal of the ELCSI-PFS research is to identify new 

safety strategies that effectively reduce crashes and promote them for nationwide installation by providing measures of their safety effectiveness and benefit to cost 

ratios through research. One of the strategies selected 

by member States to be evaluated for this study is intersection conflict warning systems (ICWS). This strategy is 

intended to reduce the frequency of crashes by alerting 

drivers of conflicting vehicles on adjacent approaches at 

unsignalized intersections, particularly those with one-way 

or two-way stop control.

Few studies have explored the safety effectiveness of 

ICWS; the effectiveness has not been shown for fourlegged intersections. This study sought to fill this 

knowledge gap.

Introduction

Providing an automated real-time system to inform drivers of suitability of available gaps for making turning 

Research, Development, and 

Technology

Turner-Fairbank Highway 

Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

www.fhwa.dot.gov/research
2

and crossing maneuvers is a recommended 

strategy in Volume 5 of the NCHRP 500 

Series Guidebooks.(1) These systems may 

be installed on the major and/or minor 

approaches of unsignalized intersections 

with stop-control on the minor approaches. 

They employ vehicle detectors to alert 

motorists of conflicting vehicles on an adjacent approach. Current installation practices 

use warning signs on the major approaches 

alerting motorists with a message stating 

“VEHICLE ENTERING WHEN FLASHING,” 

“CROSSING TRAFFIC WHEN FLASHING,” 

or “WATCH FOR ENTERING TRAFFIC.” Signs 

on the minor approaches alert entering 

motorists with “TRAFFIC APPROACHING 

WHEN FLASHING,” “LOOK FOR TRAFFIC” 

(with yellow light-emitting diode arrowshaped flashers), or visual graphic displays.

A literature review revealed that few 

research studies have considered the 

effectiveness of ICWS systems, with 

most studies focusing on speed effects or 

conflict analyses. The Missouri Department 

of Transportation (MoDOT) conducted a 

simple before-after study of the safety 

effectiveness of post-mounted ICWS 

at 9 stop-controlled intersection major 

street approaches and 10 stop-controlled 

intersection minor street approaches.(2)

The results showed a 28 percent reduction 

in total crashes, 72 percent reduction in 

severe crashes, 37 percent reduction in 

angle crashes, and a 75 percent reduction 

in severe angle crashes at the locations with 

the installation on the major street approach. 

MoDOT also found a 32 percent reduction 

in total crashes, 33 percent reduction in 

severe crashes, 44 percent reduction in 

angle crashes, and a 38 percent reduction 

in severe angle crashes at the locations 

with the minor street approach.

Simpson and Troy evaluated “Vehicle 

Entering when Flashing” signs at 56 twolane at two-lane intersections in North 

Carolina.(3) A before-after analysis was 

conducted to assess the crash reduction 

factor for multiple crash types. The following 

definitions were provided for the four 

categories of signs used in North Carolina:

• Category 1 – Overhead signs and 

flashers on major; loop on minor.

• Category 2 – Overhead signs and 

flashers on minor; loop on major.

• Category 3 – Post mounted signs and 

flashers on major; loop on minor.

• Category 4 – Locations with combination of categories 1–3.

The authors found that deployments with 

alerts on the major road in advance of the 

intersection and locations with a combination of both major and minor road alerts 

were the most effective, with Crash Modification Factors (CMFs) for total crashes of 

0.68 and 0.75, respectively. Intersections 

with four lanes on the major route were 

considered; however, no apparent reductions in crashes were found for these sites.

This study builds on these limited efforts 

using a multi-State database.

Introduction

This research examined the safety impacts 

of ICWS at rural four-leg intersections in 

Minnesota, Missouri, and North Carolina. 

Two-lane at two-lane intersections were 

considered separately from four-lane at 
3

two-lane intersections. All Minnesota 

installation sites were post-mounted, and 

all sites had a warning sign on the minor 

roadway approach. The four-lane at twolane intersections had visual displays. All 

Missouri sites were post-mounted, with 

a mix of sites on the major approaches 

and the minor approaches. North Carolina 

sites were a mix of post-mounted and/or 

overhead ICWS signs. All North Carolina 

four-lane at two-lane intersections had 

ICWS on the major approaches.

The objective was to estimate the safety 

effectiveness of this strategy as measured 

by changes in the frequency of crashes. The 

following crash types were targeted: 

• Total crashes (all types and severities 

combined).

• Injury crashes (K, A, B, and C injuries 

on KABCO scale).

• Right-angle crashes (all severities 

combined).

• Rear-end crashes (all severities 

combined).

• Nighttime crashes (all severities 

combined).

A further objective was to conduct a 

disaggregate analysis to investigate 

whether the safety effects vary by factors 

such as the type of installation, location 

of installation, the level of traffic volumes, 

the expected crash frequency before 

treatment, posted speed limit on the major 

and minor approaches, presence of turn 

lanes, presence of intersection lighting, and 

presence of “WHEN FLASHING” message. 

The evaluation of overall effectiveness 

included the consideration of the installation costs and crash savings in terms of the 

benefit-cost (B/C) ratio. 

The empirical Bayes (EB) methodology for 

observational before-after studies was used 

for the evaluation.(4) 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, Safety Performance Functions 

(SPFs) are applied. SPFs are equations used 

to estimate the predicted crash frequency 

of a site based on its characteristics that 

influence crashes (e.g., traffic volumes). 

The use of SPFs in the EB methodology 

addresses the following:

• It overcomes the difficulties of using 

crash rates in normalizing for volume 

differences between the before and 

after periods.

• It accounts for time trends.

• It reduces the level of uncertainty in the 

estimates of safety effect.

• It properly accounts for differences in 

crash experience and reporting practice 

in amalgamating data and results from 

diverse jurisdictions.

The methodology also provides a 

foundation for developing guidelines for 

estimating the likely safety consequences 

of a contemplated strategy.

The SPFs used in the EB methodology 

were estimated through generalized linear 

modeling assuming a negative binomial 

error distribution, which is consistent with 

the state of research in developing these 
4

models. In specifying a negative binomial 

error structure, an overdispersion parameter—which is used in the EB calculations—

was estimated iteratively 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, including a 

description of how the estimate of safety 

effects for target crashes was calculated.

Results

Based on the data for all three States 

combined, results are presented in two 

parts. The first part contains aggregate 

results, and the second part is based on 

a disaggregate analysis that attempted to 

discern factors that may be most favorable 

to the installation of ICWS.

Aggregate Analysis

The aggregate results for all three States 

are shown in table 1, which provides the 

estimates of predicted crashes in the after 

period without treatment, the observed 

crashes in the after period, and the estimated 

CMF and its standard error for all crash types 

considered. The percent change in crashes 

is 100×(1−Estimate of the CMF); thus, a CMF 

of 0.73 with a standard deviation of 0.035 

Total Fatal and Injury Right-Angle Rear-End Nighttime

Two-Lane at Two-Lane

EB estimate of crashes 

predicted in the after 

period without strategy

912.79 515.56 522.17 100.46 128.84

Count of crashes observed 

in the after period 670 362 420 43 116

Estimate of CMF 0.733 0.701 0.803 0.425 0.898

Standard error of estimate 

of CMF 0.035 0.045 0.049 0.073 0.096

Four-Lane at Two-Lane

EB estimate of crashes 

predicted in the after 

period without strategy

464.50 263.56 295.47 33.07 85.52

Count of crashes 

observed in the after 

period

385 212 252 33 53

Estimate of CMF 0.827 0.802 0.850 0.973 0.612

Standard error of 

estimate of CMF 0.059 0.072 0.075 0.224 0.108

Table 1. Combined results for Minnesota, Missouri, and North Carolina.
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indicates a 27 percent reduction in crashes 

with a standard deviation of 3.5 percent.

For two-lane at two-lane intersections, the 

crash type with the smallest CMF (which 

translates to the greatest reduction) is 

rear-end with a CMF of 0.425, which is 

statistically significant at the 95 percent 

confidence level. Total, fatal and injury, and 

right-angle crashes have estimated CMFs 

of 0.733, 0.701, and 0.803, respectively, 

which are also statistically significant at the 

95 percent confidence level. Nighttime 

crashes have an estimated CMF of 0.898, 

which is not statistically significant at the 

95 percent confidence level. Consideration 

should be given to the sample size used to 

develop each CMF when interpreting the 

results. For example, the sample sizes used 

to develop CMFs for rear-end and nighttime 

crashes are relatively low, resulting in larger 

standard errors and confidence intervals 

compared to the CMFs for total, fatal and 

injury, and right-angle crashes.

For four-lane at two-lane intersections, the 

crash type with the smallest CMF (which was 

statistically significant at the 95 percent 

confidence level) is nighttime crashes, with 

a CMF of 0.612. Total, fatal and injury, and 

right-angle crashes have estimated CMFs 

of 0.827, 0.802, and 0.850, respectively, 

which are also statistically significant at 

the 95 percent confidence level. Rear-end 

crashes have an estimated CMF of 0.973, 

which is not statistically significant at the 

95 percent confidence level. 

As discussed in the literature review, the 

most comprehensive study to date of ICWS 

application was conducted by Simpson and 

Troy using data from North Carolina.(3)

This report includes recommended CMFs 

for two-lane at two-lane intersections but 

does not provide recommended CMFs for 

four-lane at two-lane intersections because 

the low sample size precluded a rigorous 

analysis. Simpson and Troy recommended 

a CMF of 0.897 for total crashes and 0.878 

for injury crashes at two-lane at two-lane 

intersections.(3) Greater crash benefits were 

indicated in the present study, which are 

attributed to the following differences:

• Only four-legged intersections were 

included.

• The number of study years was limited 

to no more than five years before and 

five years after installation.

• SPFs were used to account for changes 

in traffic volumes.

• Annual multipliers were used to 

account for trends at reference sites. 

• A multi-State database was used.

Disaggregate Analysis 

The disaggregate analysis sought to identify those conditions under which the strategy is most effective. Since total, fatal and 

injury, and right-angle crashes are the focus 

of this strategy, these crash types are the 

focus of the disaggregate analysis. The following variables were identified as being of 

interest and available for all three States: 

• Installation category.

• Sign message.

• Presence of turn lanes.

• Presence of lighting.

• Presence of additional countermeasures.
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• Major and minor route average annual 

daily traffic.

• Major and minor route posted speed 

limit. 

• Predicted crash frequency in the before 

period.

For installation category, the categories 

developed by the North Carolina Department of Transportation were expanded for use in this study. Categories for 

further analysis included the following:

• Category 1 – Overhead signs and flashers at the intersection on major; loop 

on minor.

• Category 2 – Overhead signs and flashers at the intersection on minor; loop 

on major.

• Category 3a – Post mounted signs and 

flashers in advance of the intersection 

on major; loop on minor.

• Category 3b – Post mounted signs and 

flashers at the intersection on minor; 

loop on major.

• Category 4 – Locations with combination of categories 1–3.

For two-lane at two-lane intersections, all 

categories were considered in the disaggregate analysis. For four-lane at two-lane 

intersections, categories 3a and 3b were 

included in the disaggregate analysis. 

Systems in categories 1 and 2 were found 

only in North Carolina, and these systems 

were installed at the intersection on both the 

major and minor road. Category 3a signs 

were found only in Missouri and North 

Carolina and were installed in advance of 

the intersection. Category 3b systems were 

found only in Minnesota and Missouri and 

were installed at the intersection.

Table 2 provides the disaggregate results 

by category for two-lane at two-lane 

intersections and four-lane at two-lane 

intersections. The number of intersections 

is indicated for each installation category. 

For each crash type, the estimated CMF and 

standard error (in parentheses) is provided. 

The sample size used to develop the CMFs 

should be considered when applying the 

CMFs.

For two-lane at two-lane intersections, 

the results indicate statistically significant 

reductions at the 95 percent confidence 

level for all crash types for systems in 

categories 1, 3a, and 4. Considering the 

standard errors of the CMFs, it is difficult 

to make a statement about the relative 

effectiveness of categories 1, 3a, and 4; with 

the exception of the CMFs for right-angle 

crashes, the results are not statistically 

different at the 95 percent level. The 

majority of the category 4 sites consist of 

a combination of categories 1 and 2 or a 

combination of categories 3a and 3b.

For four-lane at two-lane intersections, 

the results indicate statistically significant 

reductions at the 95 percent confidence 

level for all crash types for category 3a 

and for total crashes only for category 3b 

systems. The CMFs for categories 3a and 

3b were not significantly different for any 

crash type.

It is not appropriate to compare the effectiveness of overhead versus post-mounted 

applications on the major route from the 
7

study results because the placement of 

treatment differed for the two groups. Postmounted ICWS were installed in advance of 

the intersection, whereas all overhead signs 

were installed at the intersection. Ideally, 

to consider the difference between postmounted and overhead signs, the placement should be taken into consideration. 

The Manual on Uniform Traffic Control 

Devices (MUTCD) states that warning 

signs should be placed to provide an adequate perception-response time.(5) This 

suggests that the findings in table 2 may 

be influenced by system placement, which 

could not be addressed in this research.

Table 3 presents the disaggregate results 

by predicted crash frequency in the before 

period. There was no apparent difference 

by predicted crash frequency for two-lane 

at two-lane intersections. For four-lane at 

two-lane intersections, the strategy was 

more effective when the predicted crash 

frequency was higher in the before period. 

This is logical because the strategy is often 

used at intersections with unusually high 

crashes or issues related to limited sight 

distance. For total crashes, there does 

not appear to be a benefit if the predicted 

crash frequency is less than or equal to 

three crashes per year before installation; 

Category 1 2 3a 3b 4

Two-Lane at Two-Lane

N (sites) 16 15 14 8 16

Total 0.740 (0.070) 0.892 (0.075) 0.519 (0.056) 0.886 (0.162) 0.704 (0.087) 

Fatal and Injury 0.600 (0.075) 0.944 (0.101) 0.450 (0.069) 1.064 (0.287) 0.742 (0.122) 

Right-Angle 0.807 (0.096) 1.084 (0.110) 0.454 (0.067) 1.247 (0.299) 0.697 (0.113) 

Four-Lane at Two-Lane

N (sites) N/A N/A 12 7 N/A

Total N/A N/A 0.745 (0.068) 0.690 (0.127) N/A

Fatal and Injury N/A N/A 0.734 (0.083) 0.896 (0.210) N/A

Right-Angle N/A N/A 0.769 (0.082) 0.763 (0.173) N/A

Table 2. CMFs by installation category.
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however, there is a significant reduction for 

sites with more than three predicted crashes 

per year in the before period. The results for 

right-angle crashes are significantly different from each other for sites with less than 

or equal to 2.5 predicted crashes per year 

versus sites with more than 2.5 predicted 

crashes per year before installation. There 

does not appear to be a benefit if the predicted fatal and injury crash frequency is 

less than or equal to two crashes per year 

before installation; however, there is a significant reduction for sites with more than 

two predicted fatal and injury crashes per 

year in the before period.

Additional disaggregate analyses can be 

found in the full report.

Economic Analysis 

An economic analysis was conducted to 

estimate the B/C ratio for this strategy for 

two-lane at two-lane intersections and fourlane at two-lane intersections. The statistically significant reduction in total crashes 

for combined States was used as the benefit 

for two-lane at two-lane intersections and 

for four-lane at two-lane intersections.

The average installation cost for all twolane at two-lane intersections was $41,590. 

The average installation cost was $106,158 

for four-lane at two-lane intersections. 

Additionally, a conservative annual 

maintenance and operations cost of 

$1,075 was assumed for two-lane at twolane intersections. A value of $1,200 for 

annual maintenance and utility costs was 

assumed for four-lane at two-lane sites with 

loop detectors. An annual value of $3,400 

was used for four-lane at two-lane sites 

with wireless communication. The analysis 

assumed that the useful service life for 

safety benefits was 10 years. The service 

life for loop detectors was assumed to be 

5 years. In total, 69 two-lane at two-lane 

intersections and 24 post-mounted four-lane 

at two-lane intersections were installed.

The FHWA Office of Safety R&D applies the 

Office of Management and Budget Circular 

Lanes Crash Type Crashes Per 

Year Predicted Observed CMF SE

4

Total 

≤ 3 114.23 121 1.047 0.147

> 3 350.27 264 0.751 0.062

Fatal and 

Injury 

≤ 2 66.28 74 1.101 0.179

> 2 197.28 138 0.696 0.075

Right-Angle 

≤ 2.5 93.32 116 1.228 0.176

> 2.5 202.15 136 0.669 0.075

Table 3. CMFs by predicted crash frequency in the before period.
9

A-4 discount rate of 7 percent to calculate 

the annual cost of the treatment for the 

10-year service life. With this information, 

the Capital Recovery Factor was computed 

to be 7.024 for all intersection types.

For the benefit calculations, the most 

recent FHWA mean comprehensive crash 

costs disaggregated by crash severity and 

location type were used as a base.(6) These 

costs were developed based on 2001 crash 

costs, and the unit cost (in 2001 dollars) for 

fatal and injury crashes was $158,177 and 

for property damage only (PDO) crashes 

was $7,428. This was updated to 2014 

dollars by applying the ratio of the U.S. 

Department of Transportation (USDOT) 

2014 value of a statistical life of $9.2 million 

to the 2001 value of $3.8 million.(7,8) Applying 

this ratio of 2.42 to the unit costs for PDO 

and fatal and injury crashes, and then 

weighting by the frequencies of these two 

crash types in the after period, resulted 

in an aggregate 2014 unit cost for total 

crashes of $202,060 for two-lane at twolane intersections and $219,876 for fourlane at two-lane intersections.

The total crash reduction was calculated 

by subtracting the actual crashes in the 

after period from the predicted crashes in 

the after period had the strategy not been 

implemented. The total crash reduction was 

then divided by the average number of 

after period years per site to compute the 

total reduced crashes per year. The number of total reduced crashes per year was 

65.69 for all two-lane at two-lane intersections and 19.08 for four-lane at two-lane 

intersections. Considering the number

of intersections installed, this resulted in an 

average reduction of 0.95 crashes per intersection per year for two-lane at two-lane 

intersections and 0.79 crashes per intersection per year for four-lane at two-lane intersections.

The annual benefits (i.e., dollar value of 

crash savings) were obtained by multiplying the crash reduction per site per year by 

the cost of a crash, all severities combined. 

The B/C ratio is calculated as the ratio of the 

annual benefit to the annual cost. The B/C 

ratio is estimated to be 27:1 for two-lane 

at two-lane intersections and 10:1 for fourlane at two-lane intersections. USDOT 

recommends that a sensitivity analysis be 

conducted by assuming values of a statistical life of 0.57 and 1.41 times the recommended 2014 value.(7) These factors can be 

applied directly to the estimated B/C ratios 

to get a range of 16:1–39:1 for two-lane 

at two-lane intersections and 6:1–14:1 for 

four-lane at two-lane intersections. These 

results suggest that the strategy—even with 

conservative assumptions on cost, service 

life, and the value of a statistical life—can be 

cost effective for reducing total crashes at 

four-legged intersections with stop-control 

on the minor approaches.

Summary And Conclusions

The objective of this study was to undertake 

a rigorous before-after evaluation of the 

safety effectiveness of ICWS, as measured 

by crash frequency. The study used data 

from three States—Minnesota, Missouri, 

and North Carolina—to examine the effects 

for specific crash types including total, 

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

nighttime crashes. Based on the combined 
10

results, the CMFs shown in table 4 are 

recommended for the various crash types. 

The aggregate results indicate statistically 

significant crash reductions at the 95 percent confidence level for all crash types 

except nighttime crashes for two-lane at 

two-lane intersections. The results also indicate statistically significant crash reductions 

in all crash types except rear-end crashes 

for four-lane at two-lane intersections.

The disaggregate analysis sought to identify 

those conditions under which the strategy is 

most effective. Since total, fatal and injury, 

and right-angle crashes are the focus of this 

strategy, these crash types are the focus of 

the disaggregate analysis. The disaggregate 

analysis of the results for two-lane at twolane intersections indicated larger 

percentage crash reductions for sites 

installed on the major route, particularly 

for post-mounted ICWS in advance of 

the intersection. Additional benefit may 

be provided by including the “WHEN 

FLASHING” phrase as part of the 

message. The disaggregate CMFs may 

be used in prioritizing installation sites, 

but interpretations should be made with 

caution. Particular attention should be paid 

to the sample size used to develop the 

CMFs. 

The disaggregate analysis for four-lane 

at two-lane intersections indicated larger 

percentage crash reductions for sites with 

intersection lighting and for sites with a 

higher predicted average crash frequency in 

the before period. There was no substantive 

difference for sites with warning on the 

major route versus warning on the minor 

route. The disaggregate CMFs may be 

used in prioritizing installation sites, but 

interpretations should again be made with 

caution.

Total Fatal and Injury Right-Angle Rear-End Nighttime

Two-Lane at Two-Lane

Estimate of CMF 0.733 0.701 0.803 0.425 0.898

Standard error of 

estimate of CMF 0.035 0.045 0.049 0.073 0.096

Four-Lane at Two-Lane

Estimate of CMF 0.827 0.802 0.850 0.973 0.612

Standard error of 

estimate of CMF 0.059 0.072 0.075 0.224 0.108

Table 4. Recommended CMFs based on combined States.
11

The B/C ratio estimated with conservative 

cost and service life assumptions and 

only considering the benefits for total 

crashes is 27:1 for all two-lane at two-lane 

intersections and 10:1 for four-lane at twolane intersections with post-mounted signs. 

These results suggest that the strategy—

even with conservative assumptions on 

cost, service life, and the value of a statistical 

life—can be cost effective.

As this is an evolving strategy, this study 

reflects installation practices to date. Future 

studies may show different results as 

installation practices change. In particular, 

the use of overhead ICWS on the major 

route was limited to the installations at 

the intersection (i.e., no advance warning), 

while post-mounted ICWS on the major 

route were installed in advance of the 

intersection. Future research should 

compare these installation practices, 

considering placement of warning signs. 

Specifically, Section 2C.05 of the MUTCD 

provides guidance for the placement of 

warning signs so that they provide adequate 

perception-response time.(5)

References

1. Neuman, T., Pfefer, R., Slack, K., Hardy, 

K., Harwood, D., Potts, I., Torbic, D., 

and Rabbani, E. Guidance for the 

Implementation of AASHTO Strategic 

Highway Safety Plan: Volume 5: A 

Guide for Addressing Unsignalized 

Intersection Collisions. National 

Cooperative Highway Research Program 

Report 500, Transportation Research 

Board of the National Academies, 

Washington, DC, 2003.

2. Missouri Department of Transportation. 

Missouri DOT Intersection Warning 

System Before-After Study Results. 

Accessed April 10, 2013 at http://www.

enterprise.prog.org/Projects/2010_

Present/developingconsistencyIWS/

MOIWSBeforeAfterStudy.pdf

3. Simpson, C., and Troy, S. “Safety 

Effectiveness of ‘Vehicle Entering 

When Flashing’ Signs: Evaluation of 74 

Stop-Controlled Intersections in North 

Carolina,” Transportation Research 

Record: Journal of the Transportation 

Research Board, No. 2384, National 

Research Council, Washington, DC, 

2013, pp. 1–9.

4. Hauer, E. Observational Before-After 

Studies in Road Safety – Estimating 

the Effect of Highway and Traffic 

Engineering Measures on Road Safety.

Elsevier Science, Incorporated, 1997.

5. Federal Highway Administration. 

Manual on Uniform Traffic Control 

Devices. Washington, DC, U.S. Department of Transportation, 2009.

6. Council, F., Zaloshnja, E., Miller, T., 

and Persaud, B. Crash Cost Estimates 

by Maximum Police-Reported Injury 

Severity within Selected Crash 

Geometries, FHWA-HRT-05-051, Federal 

Highway Administration, McLean, VA, 

2005.
12

FEBRUARY 2016 FHWA-HRT-15-076

HRDS-20/02-16(200)E

Researchers—Himes, Scott; Frank Gross; Kimberly Eccles; 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—Intersection conflict warning, 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 highquality 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.

7. U.S. Department of Transportation. 

Guidance on Treatment of the Value of a 

Statistical Life (VSL) in U.S. Department 

of Transportation Analyses – 2014 

Adjustment. Memo, June 13, 2014. 

Accessed November 12, 2014 at http://

www.dot.gov/sites/dot.gov/files/docs/

VSL_Guidance_2014.pdf

8. Zaloshnja E., Miller T., Council F., and 

Persaud, B. “Crash Costs in the United 

States by Crash Geometry,” Accident 

Analysis and Prevention 38(4), 2006, pp. 

644–651.