http://safety.fhwa.dot.gov 

FHWA Safety Program 

Indoor Simulator Study and Field Study 

Evaluation of Sequential Flashing Chevron Signs 

on Two-lane Rural Highways - Technical Brief 
1 

TECHBRIEF: INDOOR SIMULATOR AND FIELD STUDY EVALUATION OF

SEQUENTIAL FLASHING CHEVRON SIGNS ON TWO-LANE RURAL 

HIGHWAYS 

FHWA Publication Number: FHWA-SA-18-074

FHWA Contact: Joseph Cheung, HAS-1, (202) 366-6994, joseph.cheung@dot.gov 

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

Indoor Simulator and Field Study Evaluation of Sequential Flashing Chevron Signs on 

Two-lane Rural Highways (FHWA-SA-18-075). 

OBJECTIVE

The Federal Highway Administration (FHWA) recently published Low-cost Treatments 

for Horizontal Curve Safety 2016, which offers guidance concerning the safety effects of

various countermeasures intended to mitigate roadway departure crashes along horizontal 

curves.1 One sign application with potential safety improvements along horizontal curves 

on two-lane rural highways was the Sequential Dynamic Curve Warning System 

(SDCWS). The SDCWS is a series of horizontal curve chevron signs with solar-powered 

flashing lights embedded in the signs. The flashing lights can be simultaneous or a 

sequence of lights moving toward or away from the driver. In the sequential mode, each

sign begins flashing at a time that is offset relative to the adjacent sign, producing a

sequential flashing effect. An example SDCWS application is shown in Figure 1. 

Figure 1. Photo. SDCWS.2

The purpose of this study was to identify effective flash rates, speed-activation 

thresholds, and flashing sequences when deploying SDCWS along horizontal curves on 

two-lane rural highways. 

INTRODUCTION

In 2016, there were nearly 7.3 million police-reported crashes, resulting in 37,461 

fatalities and more than 3.1 million injuries on highways and streets in the United States.3
2 

More than 30 percent of all fatal crashes involved a single vehicle and occurred off of the 

roadway. One plausible safety management approach aims to prevent vehicles from 

leaving the roadway through encouragement of driver selection of lower speeds through 

horizontal curves via use of traffic control devices like SDCWS. Published research 

related to SDCWS is limited, but research efforts related to dynamic curve warning signs 

(DCWS), speed feedback signs, and speed-activated signs in work zones have been

documented. Studies show DCWS, speed feedback signs, and work zone speed-activated

signs are associated with decreases in driver operating speeds. (See references 4, 5, 6, 7, 

and 8.) Studies also show that continued use of DCWS produce a lasting operating speed 

reduction while speed feedback signs and work zone speed-activated signs do not have a 

lasting influence on operating speeds because these devices are not permanent. (See

references 6, 7, 8, 9, 10, and 11.) A study of 22 horizontal curve locations on rural, twolane highways in Arizona, Florida, Iowa, Ohio, Oregon, Texas, and Washington showed 

mean operating speeds were reduced by 1.8 mph one month after installation of DCWS, 

2.6 mph 12 months after installation, and 2.0 mph 24 months after installation.12 Studies 

have also shown DCWS decrease operating speeds on high- and low-traffic volume 

roads. One study evaluated the vehicle speed impact of DCWS on low-volume rural local 

roads in Minnesota.10 The before-after study showed that the unadjusted average speed 

reduction was 1.0 to 8.8 mph at the point of curvature and 1.8 to 6.3 mph within the curve 

after installation of DCWS. 

METHODOLOGY

This study examined effective flash rates, speed activation thresholds, and flashing 

sequences when deploying SDCWS along horizontal curves on two-lane rural highways 

through two evaluations. A driving simulator study at the University of Utah’s Utah 

Traffic Lab identified several SDCWS settings that impacted operating speeds and lane 

keeping behavior along a simulated version of Pennsylvania (PA) State Route 851 with 

17 horizontal curves. Sixty-eight participants (35 males, 33 females) between the ages of 

18 and 25 were recruited to participate in the study. The study employed a 3 (flashing 

pattern) x 2 (flashing rate) experimental design with a hanging control group. The three 

flashing patterns were: (1) flashing in sequence toward the driver, (2) flashing in 

sequence away from the driver, and (3) flashing in unison (i.e., simultaneous). The two 

flashing rates were: (1) slow flashing, defined as one flash per second, and (2) fast 

flashing, defined as five flashes per second. To implement this experimental design, a 

six-mile stretch of PA State Route 851 was divided into three distinct groups of curves, 

each roughly two miles in length. One of the flashing treatments (with a treatment 

distinguished by the combination of a flashing pattern and rate) was applied to each of 

these curve sections. Overall, six distinct simulator scenarios were created, each scenario 

with three distinct flashing treatments, one on each of the three defined sections of PA 

State Route 851. A seventh scenario consisted of the same three groups of curves with no 

flashing treatment. 

Based on the outcome of the simulator study, an outdoor field study was completed at 

three sites in Wisconsin to further assess the potentially effective flash rates and flashing 

patterns identified in the simulator study. Four different conditions were studied in the 

field, including a speed-activation threshold that was either 5 or 10 mph above the curve 
3 

advisory speed, two different flash rates (simultaneous and away from the driver), and 

two different flashing patterns (three flashes per second and one flash per second). A 

sample of observed operating speeds was used to create speed distributions that showed

the range of driver speed behavior at each study site. These distributions were used to 

calculate performance measures, such as the mean operating speed, standard deviation of 

speed, 85th-percentile operating speed, and the proportion of vehicles exceeding the 

horizontal curve advisory speed. 

RESULTS

This brief presents the research results in three parts. The first part contains aggregate 

results for the driving simulator study. The second and third parts are based on a 

disaggregate analysis that sought to identify the most effective flashing characteristics for 

SDCWS. 

Aggregate Analysis of Driving Simulator Data

The aggregate results of the driving simulator study did not appear to show any 

statistically significant differences in mean speed across the various flashing treatments. 

The mean speeds were generally lowest for the control condition, which was the PA State 

Route 851 scenario with only static signs and no flashing, but confidence intervals for the 

mean speed estimates corresponding to treatment and control conditions overlapped. 

With regards to lateral vehicle position, there were no consistent and statistically 

significant differences in lateral position across all treatment conditions and the control. 

Drivers tended to position the centroid of the simulator vehicle approximately one to two 

feet to the right of the center of their lane.

Disaggregate Analysis of Driving Simulator Data 

The disaggregate analysis of the driving simulator data first used a binary logit model to 

estimate the probability of one or more lane departures as a driver traverses a horizontal 

curve as a function of roadway characteristics (including curve treatments). Indicator 

variables for the six treatments indicated that none of the six applied treatments showed 

statistically significant impacts on lane departure probabilities at the 95 or 90 percent 

confidence levels when compared to the control condition. However, the treatment of low 

flashing rate away from the driver was associated with a lower probability of one or more 

lane departures and the odds ratio was statistically significant at slightly more than the 85 

percent confidence level. This is particularly interesting because speed-related findings, 

to be discussed in the next paragraph, also showed the “low-away” treatment resulting in 

a horizontal curve speed nearly 4 mph less than the control condition for drivers that 

approach a horizontal curve at 50 mph or more. 

The research team also conducted an ordinary least squares regression to model the 

potential linear-in-parameters relationship between the six different treatments, the 

control condition, and mean horizontal curve speed, while also controlling for the effect 

of other driver and roadway characteristics. The mean horizontal curve speed in this 

analysis was the mean of instantaneous speeds at the point of curvature, one-quarter point 
4 

through the curve, halfway point through the curve, three-quarter point through the curve, 

and the point of tangency. The results showed that four different flashing treatments were

associated with lower speeds than the control condition: low toward, low simultaneous, 

low away, and high simultaneous by 0.89, 1.0, 3.8, and 2.4 mph, respectively. While the 

flashing treatments were not associated with any change in speed across all drivers, they 

appeared to be effective at reducing operating speeds for drivers approaching a curve at a 

“high” operating speed (identified for this experiment as 50 mph or more, at least 5 to 10 

mph above the posted speed limit). The low-away treatment was associated with the 

lowest mean curve speed of all treatment and control conditions (and from the previous 

section, with a reduction in lane departure probability compared to all other treatments 

and the control condition). The research team made the following recommendations 

based on the overall findings of this simulator effort for consideration during the field 

evaluation: 

• Continue to explore “low-away” and “high-simultaneous” flashing treatments, as 

both resulted in the greatest and most statistically significant speed reduction 

effects on drivers approaching horizontal curves at higher speeds; “low-away” 

also resulted in the lowest probability of one or more lane departures along the 

horizontal curves. 

• Expand the driver age ranges beyond 18-25 years old to include older drivers. 

• Establish a procedure for determining a “threshold speed” over which the flashing 

treatments will be effective that can be applied across a range of roadway designs; 

using an empirical approach, the simulator study showed this threshold speed to 

be 50 mph for the study section of PA State Route 851. 

Disaggregate Analysis of Field Study Data

Based on the results of the driving simulator study, two chevron flashing patterns 

appeared to offer promise in managing operating speeds along horizontal curves of twolane rural highways. These included: (1) low flash rate away from the driver, and (2) high 

flash rate with simultaneous flashing. Because these patterns had the most pronounced 

effect on the sample of drivers approaching horizontal curves at high speeds, two speedactivation thresholds were also considered for the field study – one set 5 mph above the 

curve advisory speed and the other set 10 mph above the curve advisory speed. In total, 

five conditions were tested in the field study. The first was a baseline condition, when all 

chevrons were set in a static condition with no flashing, two conditions with the lowaway flashing sequence with two speed-activation thresholds, and two conditions with 

the high-simultaneous flashing pattern and two speed-activation thresholds. 

When considering the collective results of a speed difference analysis, defined as the 

change in operating speed between the approach tangent and the midpoint of the 

horizontal curve, there appeared to be more significant operating speed benefits for the 

sequential flashing signs during nighttime conditions than during the daytime conditions. 

During the nighttime conditions, condition #1 (simultaneous flashing pattern at a rate of 

3Hz, with a speed activation threshold 5 mph above the advisory speed) produced the 

lowest mean and 85th-percentile operating speeds relative to the baseline and other 

sequential flashing patterns. Condition #2 (same simultaneous flashing as condition #1 

with speed activation threshold that is 10 mph above the curve advisory speed) produced 
5 

operating speeds at night that were also generally lower than the baseline condition. 

Conditions #3 and #4 (flashing pattern away from the driver at 1Hz) did not have 

consistent, significant effects on vehicle operating speeds at night.

SUMMARY AND CONCLUSIONS

The objective of this study was to identify effective flash rates, speed-activation 

thresholds, and flashing sequences when deploying SDCWS along horizontal curves on 

two-lane rural highways. The study used data from an indoor driving simulator study and 

a three-site field study in Wisconsin to examine effects on lane keeping and operating 

speeds along horizontal curves if a SDCWS was present. 

Based on the indoor driving simulator study, a flashing sequence away from the driver at 

a low flash rate (1 Hz), or a simultaneous flashing pattern with a high flash rate produced 

the greatest speed reduction effects on drivers approaching horizontal curves at higher 

speeds on two-lane rural highways. The flashing sequence away from the driver also 

produced the lowest probability of a lane departure event. These two conditions were 

then evaluated in the field at three locations in Wisconsin. In addition to the flashing 

pattern and flash rate, the speed-activation threshold was also varied in the field to either 

5mph or 10mph above the curve advisory speeds. 

The field study found that, among the conditions tested, the simultaneous flashing 

pattern, set to activate at a rate of 3 Hz when a driver approached the curve more than 5 

mph above the curve advisory speed, produced the most desirable outcome based on the 

speed metrics considered in the present study. However, a flashing pattern away from the 

driver with a flashing rate of 1 Hz set to activate when approach speeds exceed the curve 

advisory speed by any amount appears to be another effective setting when the present 

field study results are assessed in conjunction with findings from the driving simulator 

study and a previous study by Smadi et al.13 

 
6 

REFERENCES

1. Albin, R., V. Brinkly, J. Cheung, F. Julian, C. Satterfield, W. Stein, E. T. Donnell, 

H. McGee, A. Holzem, M. Albee, J. Wood, and F. Hanscom. Low-Cost 

Treatments for Horizontal Curve Safety 2016. Report No. FHWA-SA-15-084, 

Federal Highway Administration, Washington, DC, January 2016. 

2. Flom, E. and Zirlin, J. “Highways For Life.” Federal Highway Administration. 

2017. Available at 

hhtp://www.fhwa.dot.gov/hfl/partnerships/safety_eval/brochure_tapco.cfm 

3. National Highway Traffic Safety Administration. Traffic Safety Facts 2016. 

Report No. DOT HS 812 456, US Department of Transportation, Washington, 

DC, 2017. 

4. Preston, H., and T. Schoenecker. Potential Safety Effects of Dynamic Signing at 

Rural Horizontal Curves. Report No. MN/RC-2000-14, University of Minnesota, 

1999. 

5. Tribbett, L., J. Mounce, and P. McGowen. An Evaluation of Dynamic Curve 

Warning Systems in the Sacramento River Canyon. Western Transportation 

Institute, Montana State University, Bozeman, MT, April 2000. 

6. Diercksen, L., C. M. Monsere, and R. L. Bertini. A Second Look at the 

Effectiveness of the Myrtle Creek Dynamic Advanced Curve Warning System. 

Proceedings from 15th World Congress on Intelligent Transport Systems and ITS 

America’s 2008 Annual Meeting, New York, NY, November 2008, 12 pp. 

7. Cruzado, I., and E. T. Donnell. Evaluating Effectiveness of Dynamic Speed 

Display Signs in Transition Zones of Two-Lane, Rural Highways in 

Pennsylvania. Transportation Research Record: Journal of the Transportation 

Research Board, No. 2122, Transportation Research Board of the National 

Academies, 2009, pp. 1–8. 

8. Mattox III, J., W. Sarasua, J. H. Ogle, R. T. Eckenrode, and A. Dunning. 

Development and Evaluation of Speed-Activated Sign to Reduce Speeds in Work 

Zones. Transportation Research Record: Journal of the Transportation Research 

Board, No. 2015, Transportation Research Board of the National Academies, 

Washington, DC, 2008, pp. 3–11. 

9. Winnett, M. A., and A. H. Wheeler. Vehicle-activated Signs: A Large-scale 

Evaluation. Report No. TRL548, Department of Transport, UK, 2002. 

10. Knapp, K. K., and F. Robinson. The Vehicle Speed Impacts of a Dynamic 

Horizontal Curve Warning Sign on Low-Volume Local Roadways. Report No. 

CTS 12-12, 2012, Humphrey School of Public Affairs, University of Minnesota, 

96 pp. 

11. Mattox III, J., W. Sarasua, J. H. Ogle, R. T. Eckenrode, and A. Dunning. 

Development and Evaluation of Speed-Activated Sign to Reduce Speeds in Work 

Zones. Transportation Research Record: Journal of the Transportation Research 

Board, No. 2015, Transportation Research Board of the National Academies, 

Washington, DC, 2008, pp. 3–11. 
7 

12. Hallmark S. L., N. Hawkins, and O. Smadi. Evaluation of Dynamic Speed 

Feedback Signs on Curves: A National Demonstration Project. Report No. 

FHWA-HRT-14-020, Federal Highway Administration, Washington, DC, 2015. 

13. Smadi, O., N. Hawkins, S. Knickerbocker, S. Hallmark, and A. Pike. Evaluation 

of the Sequential Dynamic Curve Warning System: Final Report. Report No. 

FHWA-15-CAI-012-B. Federal Highway Administration, Washington, DC, 

November 2015. 

Researchers— Eric Donnell, R.J. Porter, Milan Zlatkovic, Joel Cooper, L. Li, David 

Strayer, and Mingde Lin. 

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— two-lane rural highways, flashing chevron signs, 85th -percentile, lane 

departure, operating speed, posted speed limit, and vehicle lateral position. 

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.
FHWA, Offce of Safety 

Joseph Cheung 

202-366-6994

joseph.cheung@dot.gov

FHWA-SA-18-074