American Association of State Highway and Transportation Officials

Special Committee on Research and Innovation

FY2023 NCHRP PROBLEM STATEMENT TEMPLATE

Problem Number: 2023-G-21

Problem Title

Effective flash patterns using LED-Enhanced Chevron Sign Systems

Background Information and Need For Research

Run-off-the-road fatalities continue to be one of the most significant factors in highway safety. From 2014 to 2018 18,000 to 19,000 fatalities annually resulted from road departure. Research has identified enhanced horizontal curve warning signs as an effective countermeasure. LEDs enhance conspicuity of static traffic signs and are currently allowed in of the Manual on Uniform Traffic Control Devices (MUTCD) in section 2A.07. They are increasingly being deployed in systems across the country. The MUTCD states “LED units may be used individually within the legend or symbol of a sign and in the border of a sign…to improve the conspicuity, increase the legibility of sign legends and borders…” Section 2A.07.09 of the Manual states “if flashed, all LED units shall flash simultaneously at a rate of more than 50 and less than 60 times per minute.” The flash rate and pattern may play a significant role in improving the performance of this countermeasure. Research to date has not focused on flash pattern and simply used either simultaneously or sequentially flash patterns. The purpose of this study is to determine the most effective flash patterns and flash durations for LED-enhanced chevrons in varying applications, seeking eventual approval by the Federal Highway Administration (FHWA) and standardization of flash pattern naming conventions for inclusion in the MUTCD.

Sequential chevron systems have been identified as a proven low-cost countermeasure for reducing roadway departure crashes at horizontal curves by the FHWAi. Roadway departure crash rates are three times higher at horizontal curve locations relative to tangent segments of roadwayii. These systems have been implemented as a countermeasure on two-lane rural highway curves as a means of reducing vehicle operating speeds and improve curve delineation. An example of the results of

an FHWA study utilizing sequencing chevrons showed that after 24 monthsiii:

• The change in % of vehicles exceeding the advisory speed by 20 mph or more decreased by an average of 32 percent.

• The change in % of vehicles exceeding the advisory speed by 15 mph or more decreased by an average of 30 percent.

Sequential chevrons can effectively reduce vehicle speeds in horizontal curves especially in wet conditions and a Caltrans study reported a 44 percent reduction in crashes in the first year and a 39 percent reduction in the second year.iv Speed reduction is vital, due to the fact that, in the US, drivers who exceed the speed limit or advisory speed are involved in nearly one-third of all fatal crashes and each year more than 13,000 people in the US are killed in speed-related crashesv.

To date, flash patterns have been simultaneous (i.e., each sign is flashing at the same time as the other signs); or, sequential (i.e., in a series of chevrons signs where the LED activate moving away from the driver). In the latter case, this is typically accomplished by having each sign flash at least once per second, with each flash lasting 100 milliseconds to 1 second. Each sign begins flashing at a time that is offset relative to the adjacent sign, producing a sequential flashing effect. At least one sign is always on in the system during the flash pattern. This gives the effect of the system guiding or pulling the driver through the curve and highlights the geometry while still meeting the MUTCD guidelines.

Using the length and speed of the curve, the user can set each of the W1-8 chevron signs to flash in a specific sequence or time interval. Each curve design will have different sign placement and geometry for consideration when determining the appropriate flash sequence. Chapter 2C of the Manual on Uniform Traffic Control Devices (MUTCD) and engineering judgment should be applied when determining appropriate sign layouts and locations.

Typically, each LED-enhanced sequencing chevron sign on a horizontal curve will flash at least once per second according to MUTCD guidelines, with a flash "ON" time of 100 milliseconds to 1 second. Again, not all curves are configured the same and some are longer than other. When curves are long and there are numerous chevrons, vehicles can lose visibility of the flash pattern due to length of time between flashes. This has the potential to reduce the effectiveness of the LED-enhanced chevron sign systems. As an alternative, alternating flashing of pairs of chevrons signs provides shorter segments allowing the flash to be visible throughout the traversal of the horizontal curve. This allows the motorist to see the LED-enhanced chevrons flashing no matter where the vehicle is positioned in the curve and where the system is in its flash pattern.

Literature Search Summary

Information Sources:

i Federal Highway Administration Low-Cost Treatments for Horizontal Curve Safety 2016, APPENDIX E: Application of Sequential Dynamic Curve Warning Systems (SDCWS). https://safety.fhwa.dot.gov/roadway_dept/horicurves/fhwasa15084/appe.cfm

ii US Department of Transportation FHWA report Low-Cost Treatments for Horizontal Curve Safety 2016

iii Smadi, O., N. Hawkins, S. Hallmark, and S. Knickerbocker. Evaluation of the Sequential Dynamic Curve Warning

System. Report No. FHWA-HIF-13-040, Federal Highway Administration

iv McGee, Hugh W. and Hanscom, Fred R. (2006), US Department of Transportation FHWA report Low-Cost

Treatments for Horizontal Curve Safety.

v USDOT Report: FHWA-HRT-12-020. (2015) Evaluation of Dynamic Speed Feedback Signs on Curves

Other Research:

Indoor Simulator Study and Field Study Evaluation of Sequential Flashing Chevron Signs on Two-lane Rural

Highways, FHWA-SA-18-075, FHWA, by Penn State, November 2017

Evaluation of the Sequential Dynamic Curve Warning System, FHWA-15-CAI-012-A, by Iowa State, November 2015

Factors Related to Fatal Single-Vehicle Run-off-road Crashes, DOT HS 811 232, NHTSA, by URC Enterprises, Inc., November 2009.

Run-off-road Crashes: An On-Scene Perspective, DOT HS 811 500, NHTSA, July 2011.

Practices for Preventing Roadway Departures – Synthesis, NCHRP 515, TRB, by Hugh McGee, 2018.

Research Objective

To improve the safety countermeasure characteristics of LED-enhanced chevron (W1-8) signs determining the best results from allowable flash rate and patterns such as constant on, simultaneous, sequential, and alternating would be researched. Additionally, wherever practical, study the correlation, if any, between reducing vehicle speeds at different flash durations and actual speeds of the sequence.

Since several enhanced conspicuity chevron sign systems are in the field presently, the first step would be to inventory the applications in the US, assembling a context and performance data base. A synthesis study would be used to obtain this data. A subsequent research effort may be necessary depending upon findings from the synthesis (for example, if flash rate and pattern options show varying performance the need to conduct more thorough research into the best flash rates and patterns). A draft of such follow up research is also provided here.

PHASE 1 SYNTHESIS

a. Survey of state DOT (AASHTO), county (NACE), local agency (APWA) and transportation (ITE) professionals to identify applications of chevron signs using enhanced conspicuity LEDs.

b. Follow up with professionals for each application to obtain the following information:

• Location/Route

• Lane configuration, grade, speed limit

• Pictures of application

• LED flash rate(s), flash pattern(s)

• Curve radius and advisory speed

• Chevron sign spacing

• Speed distributions (before/after, as available)

• Crash data (before/after, as available)

c. Tabulate survey data of current practices and results

d. Summarize findings in a synthesis report and determine if further research may be necessary to identify the “best” enhanced conspicuity strategy(s) for flash rate and pattern.

e. Share findings with the National Committee on Uniform Traffic Control Devices, AASHTO, NACE and APWA.

PHASE 2 FLASH RATE/PATTERN RESEARCH (draft work plan to consider,if necessary, based upon synthesis work)

a. Task 1 – Assessment of Existing Research

This would involve literature search into run-of-the-road and LED-enhanced traffic control devices, both those currently available in the industry and concepts in development. Findings would be summarized in an annotated bibliography of prior research, focusing on flash pattern evaluations.

b. Task 2 – Simulator Testing of Flash Patterns

Simulator research will be conducted for various approach speed and flash patterns, analyzing driver-subject behaviors and outcomes. A task report will highlight results of the flash patterns and best performance. The report will recommend open road testing strategies for Task 3.

c. Task 3 – Open Road/Test Course Evaluation of Flash Patterns

A series of signs will be assembled for various curve radius conditions. Test subjects will drive vehicles at various approach speeds and connected vehicle data and driver observation systems will assess performance for the various flash patterns, given curve radii and speeds, to assess the best performance. A task report will outline test conduct, results, and findings.

d. Task 4 – Field Testing

Participating agencies (and vendors noted in 3a Phase 1) will install the best performing flash patterns in the field for high crash locations associated with road departure. After three years, after crash data will be assess and compared with identified other existing locations where LED-enhanced signs were installed (sites to be identified in Phase 1) as control comparisons for crash reduction (this will include the following installations – from existing baselines sites with no chevron signs to static speed advisory and/or chevron signs, to LED-enhanced conspicuity chevron signs (best option). A task report will summarize crash reduction performance of field tests to control comparisons.

e. Task 5 - Final Analysis and Evaluation

The final project report including results from Phases 1-4 will be prepared.

Urgency and Potential Benefits

Run-off-the-road crashes are one of the largest categories of highway fatalities and serious injuries every year. With the changes to the impending MUTCD related to signing for horizontal curves, many agencies will be updating signs in the immediate future. Having research into the best systems for preventing run-off-the-road crashing at horizontal curves would allow agencies to utilize emerging national and local safety funding to significantly reduce run-of-the-road crashes. This synthesis (and if needed, research) will provide practitioners better understanding to the best applications for flash rate and flash pattern for enhancing chevron signs with LEDs. In doing so, limited funding can be for efficiently applied once, immediately, rather than allow non-uniform applications to emerge that will eventually need to be removed, wasting resources

Implementation Considerations

The strategy would be to complete the synthesis study immediately and funding for just this phase would be step 1. With the findings from the synthesis, information would be shared with the NCUTCD for their consideration. In the findings of the synthesis, should it appear that further research would be necessary, a refined problem statement would be prepared to seek further funding for more detailed research (along the lines as preliminarily outlined in this synthesis problem statement (which has been provided to help synthesis analysts to better understand their undertaking. The target audience for the synthesis will be agencies that are designing, installing and operating curve warning systems (likely state DOTs and county engineers). By conducting the synthesis, greater understanding of current knowledge and practice can be obtained. By sharing this with professionals in transportation agencies and national committees, they can advance thinking and applications into how to reduce run-off-the-road crashes.

Recommended Research Funding and Research Period

Level of Effort:

Phase 1 Synthesis: one person month survey outreach and synthesis, one person week summary of findings

Total: 240 hours ~ $45,000

Problem Statement Author(s): For each author, provide their name, affiliation, email address and phone.

The initial draft of this problem statement was developed by Bob Felt from TraffiCalm Systems, Joanne Conrad and Jay Swinea from TAPCO, Randy McCourt from DKS Associates whom all are members of the NCUTCD RWS Technical Committee Special Research Task Force on sequential flash patterns.

Potential Panel Members: For each panel member, provide their name, affiliation, email address and phone.

Tom Heydel

SE Regional Traffic Engineer

Wisconsin DOT

Tom.heydel@dot.sate.wi.us

Chair: Regulatory & Warning Signs Technical Committee of the NCUTCD

Person Submitting The Problem Statement: Name, affiliation, email address and phone.

The initial draft of this problem statement was developed by Bob Felt, Joanne Conrad and Jay Swinea, Randy McCourt whom all are members of the Regulatory & Warning Signs Technical Committee of the NCUTCD Special Research Task Force on sequential flash patterns.

Randy McCourt Bob Felt

ITE Past President Traffic Calm Systems

503.randy.mccourt@gmail.com bob.felt@trafficalm.com

503.753.8996 855.738.2722