TECHBRIEF Simulator Evaluation of LowCost Safety Improvements

on Rural Two-Lane Undivided 

Roads: Nighttime Delineation

for Curves and Traffic 

Calming for Small Towns

FHWA Publication No.: FHWA-HRT-09-062

FHWA Contact: Roya Amjadi, HRDS-06, (202) 493-3383, 

roya.amjadi@dot.gov

This document is a technical summary of the Federal Highway 

Administration report, Simulator Evaluation of Low-Cost 

Safety Improvements on Rural Two-Lane Undivided Roads: 

Nighttime Delineation for Curves and Traffic Calming for Small 

Towns, FHWA-HRT-09-061.

Objective

The Federal Highway Administration (FHWA) organized 26 States 

to participate in the FHWA Low Cost Safety Improvements 

Pooled Fund Study as part of its strategic highway safety plan 

support effort. The purpose of the pooled fund study is to 

estimate the safety effectiveness for several of the unproven 

low-cost safety strategies identified in the National Cooperative 

Highway Research Program (NCHRP) Report 500 Series.

(1) One 

of the strategies chosen to be evaluated for this study is 

improved curve delineation, which is intended to reduce the 

frequency of curve-related crashes by providing more conspicuous signing and lane markings.

In this study, a driving simulator experiment was conducted to 

evaluate two sets of alternative low-cost safety improvements 

for rural areas based on Technical Advisory Committee 

recommendations from the 2007 Annual Meeting. The first set 

of improvements was directed toward enhancing the visibility 

of curves on rural two-lane undivided roads at night. It focused 

on achieving advanced detection and speed reduction in such 

curves. The second set of improvements was directed toward 

slowing traffic on rural two-lane undivided roads in small towns 

during the day by focusing on traffic calming within the towns. 

Research, Development, and 

Technology

Turner-Fairbank Highway 

Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

www.tfhrc.gov
2

Introduction

Treatment for Curves

Part of this study investigated low-cost visibility

enhancements for navigating rural horizontal 

curves at night. According to the Fatality Analysis Reporting System, of the 37,248 fatal crashes 

in 2007, 6,495 (17.4 percent) were on horizontal 

curve sections of two-lane rural roads.(2) Of 

those, 2,739 crashes (42.2 percent) occurred at 

night. Previous data have indicated that approximately 25 percent of all vehicle miles traveled 

(VMT) occur at night. Rural local roads may have 

less than 25 percent of VMT occurring at night.

Even if the total VMT is adjusted for the more 

conservative total, the exposure rate is more 

than twice as high during the night compared 

to the day. Thus, fatal crashes on rural curves at 

night represent an important crash category, and 

improving the visibility of rural curves at night 

has been shown to reduce this type of crash.(3) 

To help enhance the visibility of curves, edge 

lines and post-mounted delineators (PMDs) were 

selected as the best alternatives for the simulator study. A synthesis of research has shown 

that introducing and enhancing edge lines has a 

wide range of results, from decreasing vehicle 

speeds by 3.1 mi/h (4.9 km/h) to increasing vehicle 

speeds by 6.6 mi/h (10.6 km/h).(4) Although the 

overall effect of combining the results of multiple 

studies was not statistically different from zero, 

individual experiments showed results different 

from zero. In terms of driver preview distances 

for curves driven at night, Molino et al. calculated

anywhere from a 12- to 70-percent improvement 

in curve detection distances due to enhanced 

edge lines.(5) 

PMDs have also been found to reduce crash 

rates on relatively sharp curves during the night. 

Agent and Creasey performed field and laboratory investigations which indicated that PMDs 

had a beneficial effect; however, pavement markings had an even greater beneficial effect based 

on vehicle speed and lane encroachment.(6)

Meanwhile, Montella evaluated the safety effectiveness of various horizontal curve delineation 

treatments in Italy.(7) A novel treatment using 

sequential flashing beacons was part of this 

evaluation. When sequential flashing beacons 

were added to chevrons and curve warning signs, 

the reported number of crashes decreased by 

77 percent compared to the expected number 

using an Empirical Bayes analysis.

Treatments for Towns

In 2003, 86 percent of speeding-related fatalities 

occurred on roads that were not interstate highways, and the highest speeding-related fatality 

rates occurred on local and collector roads where 

the lowest speed limits were posted, suggesting that research should be conducted to identify and promote engineering measures to better manage speed.(8) In addition, research should 

be performed to achieve appropriate speeds on 

main roads through towns that are not suitable 

for traditional traffic calming techniques. This 

simulator study investigated the speed calming 

effects of chicanes located at the beginning and 

end of a town. There are several resources available regarding the design of chicanes, but their 

effectiveness has not been determined with 

rigorous research. Traffic Calming: State of the 

Practice refers to an installation of chicanes and 

speed tables in Montgomery County, MD, where 

speeds decreased from 34 to 30 mi/h (54.7 to 

48.3 km/h), and volume decreased from 1,500 to 

1,390 vehicles per day.(9) Marek and Walgren 

found that chicanes were effective at reducing 

85th-percentile speeds at four different locations

in Seattle, WA, with reductions between 5 and 

13 mi/h (8.05 and 20.93 km/h) inside the chicane 

area and 1 and 6 mi/h (1.61 and 9.7 km/h) outside 

the chicane area (after the chicane has been 

passed).(10) 

Additionally, bulb-outs were evaluated at intersection locations in a town for this study. Bulbouts are curb extensions that are designed to 

slow drivers down. King analyzed the effect of 

bulb-outs in New York City, NY, and found that at 

four of six surveyed locations, the overall severity rates for crashes were reduced after bulb-outs 

were installed.(11) Furthermore, at two of three 

locations, the injury severity rates were also reduced. Huang and Cynecki performed an analysis at two locations in both Cambridge, MA, and 

Seattle, WA, to determine whether drivers would 

yield to pedestrians with the addition of bulb-out
3

treatments.(12) The results for Cambridge were 

inconclusive. In Seattle, there was no change in 

vehicle yielding behavior.

Methodology

Participants

Participants were licensed drivers between the 

ages of 18 and 88 with a mean age of 57.6. Of 

the 36 participants who completed the experiment, half were under the age of 65 (the age 

range was 18–64 with a mean age of 41.7), and 

half were above the age of 65 (the age range was 

66–88 with a mean age of 73.6). Each age group 

(younger and older) was evenly distributed 

between males and females. Although the sample 

of participants was balanced for age and gender, 

these factors were not analyzed in the experiment. 

Driving Simulator

FHWA’s Highway Driving Simulator (HDS) is a relatively high-fidelity research simulator. Simulator 

components include a 1998 Saturn SL1 automobile chassis, five projectors, and a cylindrical 

projector screen with 240 degrees of forward 

view. Under the vehicle chassis, there is a 

3 degree-of-freedom motion system. A sound 

system provided engine, wind, tire, and other 

sounds. A microphone was used to record the 

verbal responses made by the participants.

Experimental Sessions

Each participant received all treatment conditions. 

In addition, each curve or town was separated 

by a long tangent segment of roadway. The 

drives consisted of 26 trials, 20 curves, and 

6 towns in a quasi-random order all separated by 

a tangent. The participants completed three 

such drives. The simulated driving condition 

instantly changed to night for curves and to 

day for towns.

Simulated Treatments for Curves

All of the curves and their preceding tangents 

consisted of two-lane rural roadways. Participants drove through the curves at night with no 

fixed roadway lighting. There was no traffic on 

the roadway in either direction because the glare 

from oncoming headlights was more difficult to 

simulate. Therefore, it was decided to employ 

basic driving conditions without any traffic. The 

rural tangent and curve roadway segments had 

lane widths of 11 ft (3.4 m) with 3-ft (0.9-m) paved 

shoulders on either side. The radius of curvature 

was either 100 ft (30.5 m) for the sharp curves 

or 300 ft (91.5 m) for the less sharp curves. 

The deflection angle was 60 degrees for both 

types of curves. The term gentle was used to 

distinguish the less sharp curves for the research 

participants. There were an equal number of 

right-hand and left-hand curves. The simulator 

could reproduce the effects of superelevation 

only to a certain degree, so it was decided not to 

employ it. There were no curve warning signs 

preceding the curves. Advance warning signs 

were not employed so as to measure the effects 

of the pavement markings and the PMDs themselves to enhance driver detection of curves 

ahead. At the beginning of half of the tangent 

sections, there was a speed limit sign indicating 

55 mi/h (88.5 km/h). 

For the curves, the baseline condition consisted 

of standard 4-inch (101.6-mm)-wide double 

yellow centerlines on the roadway, both on 

the preceding tangent and on the curve itself. 

The first level of low-cost safety improvement 

beyond the centerlines was the addition of a 

conventional 4-inch (101.6-mm) white edge line 

to both sides of the roadway on the preceding 

tangent as well as on the curve. The next level 

of improvement involved the application of 

various configurations of reflectorized PMDs 

as an addition to the white edge lines and 

yellow centerlines. 

The first PMD configuration was the standard 

installation of delineators on the far side of 

each curve. The second PMD configuration 

employed the same standard layout of delineators except on both sides of the roadway. The 

third configuration employed similarly spaced 

PMDs with simulated light-emitting diode (LED) 

lamps at the top of each post (above the standard reflector panel). These enhanced delineators 

were located on the far side of each curve. The 

LED lamps were programmed to create a repetitive streaming light pattern moving in the 

direction of the curve. The LED lights streamed 
4

faster for sharp curves and slower for gentle 

curves. The repetition rate of the streaming light 

patterns was 3 Hz for sharp curves and 1 Hz 

for gentle curves. Thus, the LED-enhanced delineators provided information on both the direction and the severity of approaching curves. 

These streaming lights operated continuously. 

The edge lines were always present with the 

addition of any of the PMD conditions, reflecting common implementation practice. Each 

experimental drive contained 20 curve conditions in a different order (5 treatments for 

4 types of curves).

Responses to Curves

Participants were instructed to verbally indicate 

the direction and severity of each approaching curve as soon as they were confident that 

they could identify the particular roadway feature. Participants were instructed to say “right” or 

“left” as soon as they could predict the direction 

of the curve and “sharp” or “gentle” as soon 

as they could predict the curve’s severity. The 

time of their verbal responses was recorded and 

converted into distance from the point of curvature (PC) of the curve. The participants were 

instructed to drive at 55 mi/h (88.5 km/h) in all 

preceding tangent sections of the roadway. 

Otherwise, they were instructed to drive as they 

normally would.

Simulated Treatments for Towns

For the town portion of the experiment, a single

small town was simulated, and it was approached an equal number of times from each 

direction. The town was always presented in 

simulated daylight, and it consisted of a main 

two-lane roadway with marked parking spaces 

on each side. Each town segment was about 

450 ft (137.3 m) long, and it was preceded and 

followed by a long rural tangent. There was 

no traffic on the roadway in either direction. In 

addition, there were no pedestrians or speed 

limit signs leading up to or in the town. 

The baseline condition consisted of standard 

4-inch (101.6-mm)-wide double yellow centerlines 

on the roadway—both on the preceding tangent 

and in the town itself. The first low-cost safety 

improvement beyond the centerlines was the 

addition of bulb-outs at all intersections in the 

town. These bulb-outs were simulated as curb 

and gutter modifications. In addition, a less 

expensive bulb-out configuration was implemented by means of pavement markings alone. 

Each travel lane was 11 ft (3.4 m) wide in the 

bulb-outs.

By way of contrast to the baseline condition, an 

additional condition was investigated with cars 

parked in most of the marked parking spaces 

on both sides of the main road. The next lowcost safety improvement consisted of chicanes 

at the entrance and exit of the town. These 

chicanes were first implemented in the standard 

manner by means of curb and gutter modifications. The chicanes were also implemented 

by means of pavement markings only. For the 

chicanes, the minimum radius of curvature was 

approximately 325 ft (99.1 m), and the shifts 

were sufficiently gradual over a total distance 

of 88 ft (26.8 m) to maintain speeds of approximately 20 mi/h (32.2 km/h). These gradual shifts 

were also designed to minimize truck off-tracking and to facilitate emergency vehicle use. 

Each experimental drive contained one of the 

six conditions in a different order, with three 

approaches from each direction.

Results

Speed Profiles for Curves

Figure 1 shows the average driving speed as 

a function of distance from the PC for the five 

curve treatment conditions as well as for the 

baseline condition. The data in figure 1 represent speed profiles in terms of average speeds 

across the 36 research participants, 4 curve geometries, and 3 drives. The error bars represent 

1 standard error of the mean. The speed profiles 

indicate a constant portion in the far tangent, 

then a rapid deceleration, followed by a shallow 

dip. The treatments tended to organize themselves into two groups: (1) pavement markings 

(baseline and edge lines) and (2) delineators 

(single side PMDs, both sides PMDs, and streaming PMDs). This treatment effect was statistically 

significant (F (4, 32) = 51.7, p < 0.001). The delineators were more effective than the pavement 

markings in slowing the drivers down sooner 
5

and to a greater degree. For distances of under 

600 ft (183 m), the consistent treatment effect 

was evident over the entire range of locations 

without any order reversals.

Speed Reduction and Feature Detection 

for Curves

Table 1 summarizes the potential safety advantages in terms of speed reduction and feature 

detection distance for the curves. Based on 

speed measurements at the point of curvature, 

column 2 shows the estimated average speed 

reductions for the various curve visibility 

improvements (relative to the baseline, rounded 

to the nearest 1 mi/h (1.6 km/h)), and column 5 

shows the corresponding speed reduction rankings for each (from best to worst).

Drivers performed almost perfectly in detecting the direction of curves ahead in the road 

(99.7 percent correct). In table 1, column 3 shows 

the estimated average curve direction detection 

distance increases for each treatment (relative to

the baseline, rounded to the nearest 5 ft 

(1.5 m)),and column 6 shows the corresponding 

detection distance rankings for each. Compared 

to curve direction detection, drivers did not perform as well on curve severity detection (only 

82.5 percent correct). While this performance 

was better than chance, drivers had more difficulty detecting the severity of a curve than 

detecting its direction. Column 4 shows the 

estimated average curve severity detection distance increases for each treatment, and column 7 

shows the corresponding severity detection 

rankings for each treatment. 

A comparison of findings across the three 

response categories in table 1 reveals two important relationships. First, if the standard reflectorized PMD conditions are collapsed (single versus 

both sides), there is a consistent order across 

all three response categories (speed plus direction and severity distances). The enhanced PMDs 

with streaming lights performed the best followed by the standard reflectorized PMDs, and 

the edge lines performed the weakest or showed 

no improvement. Second, the enhanced PMDs 

with streaming lights performed exceptionally 

well in terms of increasing curve feature detection but only moderately well in terms of 

slowing drivers down.

Speed Profiles for Towns

Figure 2 shows the average vehicle speed as a 

function of distance from the beginning of the 

town for the six different town treatment 

conditions. The data in figure 2 represent speed 

Figure 1. Average speed as a function of the 

distance from the PC.

Table 1. Estimated safety advantages and rank ordering of treatments for curves.

Treatment

Speed 

Reduction 

(mi/h)

Direction

Distance

Increase (ft)

Severity

Distance

Increase (ft)

Speed 

Reduction

Rank

Direction

Rank

Severity

Rank

Enhanced PMDs with 

streaming LED lights 9 1,065 560 1 1 1

Standard PMDs on both 

sides of the road 8 130 45–65 2 3 2

Standard PMDs on a 

single side of the road 7 200 45–65 3 2 2

4-inch edge lines 2 25 0 4 4 3
6

profiles in terms of averages for the 36 research 

participants over the 3 drives. The error bars represent 1 standard error of the mean. Positive distances indicate measurement locations ahead 

of the town, and negative distances indicate 

locations in the town.

The speed profiles in figure 2 indicate a 

gentle deceleration followed by a plateau. 

The treatments were organized into three 

groups: (1) baseline and bulb-outs (baseline, curb 

and gutter bulb-outs, and painted bulb-outs), 

(2) parked cars, and (3) chicanes (curb and gutter

chicanes and painted chicanes). This treatment effect was statistically significant (F (5, 30) =

12.5, p < 0.001). The shapes of the speed profile 

functions were similar for all of the five types 

of safety countermeasures except the chicanes. 

For all other countermeasures, the minimum 

speed was achieved near the middle of the 

town or slightly further into the town. For the 

chicanes, the minimum speed was achieved 

at the beginning and end of the town where 

the chicanes were located. In the town itself, 

the speed increased for the chicane conditions, reaching a local maximum at the middle

of the town and decreasing again for the 

second chicane.

Speed Reduction for Towns

The major findings regarding the relative advantages of the various speed calming treatments 

for small towns are summarized in table 2. 

For both locations at the beginning and middle 

of the town, table 2 shows estimated average 

speed reductions (relative to the baseline condition) of the tested safety improvements as well 

as their rank ordering (from best to worst). 

Both types of bulb-outs produced either a very 

small reduction in speed or did not show improvements from the baseline. In general, chicanes produced the greatest reduction in speed.

Summary

Potential Safety Benefits for Curves

For curves, the results of the experiment indicated that edge lines offered a small potential 

safety benefit. Adding standard reflectorized 

PMDs used with edge lines offered a somewhat greater benefit. In general, standard reflectorized PMDs with edge lines performed better

than pavement markings alone. This result 

does not imply that edge lines are not needed; 

edge lines provide continuous delineation of 

the travel lane, especially at close range. Of all 

the treatments explored, the streaming PMDs 

Figure 2. Average speed as a function of the 

distance from the beginning of the town.

Table 2. Estimated speed reductions and rank ordering of treatments for towns.

Treatment

Beginning of 

Town Speed 

Reduction (mi/h)

Middle of Town 

Speed Reduction 

(mi/h)

Beginning of 

Town Rank

Middle of 

Town Rank

Curb and gutter chicanes 9 5 1 1

Painted chicanes 6 4 2 2

Parked cars on both sides of 

the road 4 4.5 3 2

Painted bulb-outs or curb and 

gutter bulb-outs 0 1 None 3
7

with edge lines offered the most potential safety 

benefit. Presently, the streaming PMD solution has not been developed for two-lane rural 

roads, nor are the potential future cost implications of implementing this countermeasure 

known at this time. Further research is recommended including economic analysis and field 

validation studies.

Potential Safety Benefits for Towns

For towns, the results indicated that bulb-outs 

offered a small potential safety benefit or no 

benefit at all. Painted chicanes and parked cars 

on both sides of the road offered a greater 

benefit, and curb and gutter chicanes offered 

the most potential safety benefit. In general, 

chicanes and parked cars performed the best 

as traffic calming countermeasures. The painted 

chicanes and parked cars solution proved to 

be an effective and low-cost speed-calming 

measure. 

However, the above results have not been validated in the field. Simulation of driving through 

a small town does not take into account all of 

the hazardous factors involved in actually driving through a town. In addition to concerns about 

parked cars, especially in cases where there is 

only one travel lane in each direction, attention 

needs to be paid to assessing and balancing 

the possible safety hazards of vehicles, drivers, 

passengers, and pedestrians entering the roadway. The parked cars solution also raises some 

potential problems for bicycle traffic. Concerning 

chicanes, especially in cases without a separating 

median, attention needs to be given to assessing and balancing the possible safety hazards 

of head-on or sideswipe opposite-direction 

crashes. In general, bulb-outs and chicanes 

should only be implemented in well-lit areas.

Conclusion

The present experiment focused on two areas: 

(1) the advanced detection and speed reduction 

for curves in rural two-lane roads at night and 

(2) traffic calming for small rural towns during 

the day. For curves, PMDs used with edge lines

performed better in terms of slowing drivers 

down than pavement markings alone. The 

novel streaming PMDs solution offered the 

most dramatic potential benefit in terms of 

advanced curve detection, and this solution is 

worthy of further study. For towns, chicanes 

slowed drivers down the most followed by 

parked cars on both sides of the road. Further 

study and consideration should be given to 

adding painted chicanes to town entrances and 

providing for and encouraging parking in towns.

References

1. National Cooperative Highway Research 

Program. (2003). “Guidance for Implementation of the AASHTO Strategic Highway 

Safety Plan,” NCHRP Report 500 

Series, Transportation Research Board, 

Washington, DC.

2. National Highway Traffic Safety Administration. Fatality Analysis Reporting System, U.S. Department of Transportation, 

Washington, DC. Obtained from: http://

www.fars.nhtsa.dot.gov. Site last accessed 

October 23, 2009.

3. Fitzpatrick, K., Balke, K., Harwood, D.W., 

and Anderson, I.B. (2000). “Accident 

Mitigation Guide for Congested Rural TwoLane Highways,” NCHRP Report 500 Series, 

Vol. 440, Transportation Research Board, 

Washington, DC.

4. van Driel, C.J.G., Davidse, R.J., and van 

Maarseveen, M.F.A.M. (2004). “The Effects of 

an Edgeline on Speed and Lateral Position: 

A Meta-Analysis,” Accident Analysis and 

Prevention, 36(4), 671–682.

5. Molino, J., Katz, B., Duke, D., Opiela, K., 

Andersen, C., and Moyer, M. (2004). Field 

Validation for the Relative Effectiveness 

of Combinations of Pavement Markings 

and RRPMs in Recognizing Curves at 

Night, TRB 2004 Annual Meeting 

CD-ROM, Transportation Research Board, 

Washington, DC.

6. Agent, K.R. and Creasey, T. (1986). Delineation 

of Horizontal Curves, Interim Report UKTRP86-4, University of Kentucky, Lexington, KY. 
8

Researchers—This study was performed by the Human Centered System Team of the Federal 

Highway Administration’s (FHWA) Office of Safety Research and Development. John Molino was the 

Principal Investigator. Bryan Katz, Vaughan Inman, Megan Hermosillo, Erin Dagnall, and Jason Kennedy 

assisted in conducting the experiment. The simulation was led by Jason Williams with assistance from 

Peter Chou, Ryan Cartwright, and Michael Baumgartner. For more information about this research, 

contact Roya Amjadi, FHWA Task Manager, HRDS, (202) 493-3383, roya.amjadi@dot.gov.

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.tfhrc.gov/

safety.

Key Words—Roadway safety, Visibility, Curve navigation, Pavement markings, Edge lines, Postmounted delineators, Traffic calming, Bulb-outs, Chicanes, Parked cars, Safety countermeasures, and 

Driving simulators.

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.

7. Montella, A. (2009). Safety Evaluation of 

Curve Delineation Improvements: An 

Empirical Bayes Observational BeforeAfter Study, TRB 2009 Annual Meeting 

CD-ROM, Transportation Research Board, 

Washington, DC.

8. National Highway Traffic Safety Administration. (2005). Speed Management Strategic 

Initiative, Publication Number DOT-HS-809-

924, U.S, Department of Transportation, 

Washington, DC.

9. Ewing, R. (1999). Traffic Calming: State of the 

Practice, Institute of Transportation Engineers, 

Washington, DC.

10. Marek, J.C. and Walgren, S. (1998). Mid-Block 

Speed Control: Chicanes and Speed Humps, 

Seattle, WA. Obtained from: http://www.

seattle.gov/transportation/docs/ITErevfin.pdf. 

Site last accessed October 23, 2009. 

11. King, M.R. (1999). “Calming New York City 

Intersections,” Urban Street Symposium 

Conference Proceedings, Transportation 

Research Board, Washington, DC.

12. Huang, H.F. and Cynecki, M.J. (2000). “Effects 

of Traffic Calming Measures on Pedestrian 

and Motorist Behavior,” Transportation 

Research Record 1705, Transportation 

Research Board, Washington, DC.

november 2009 FHWA-HRT-09-062

HRDS-06/11-09(1M)E