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The National Academies

NCHRP 03-106 [Completed]

Traffic Control Device Guidelines for Curves

  Project Data
Funds: $500,000
Research Agency: Texas A&M Research Foundation
Principal Investigator: Paul Carlson
Effective Date: 6/19/2012
Completion Date: 4/18/2015

OBJECTIVE
 
The objective of this research was to identify potential improvements to the MUTCD guidelines for the application of traffic control devices on curves (particularly curve/turn warning signs, advisory speed plaques, chevrons, and large arrow panels). The improved guidelines include (1) conditions to consider in deciding whether a particular TCD should be installed (e.g., traffic volume, crash history, speed, difference between the posted speed limit and the advisory speed for the curve) and (2) descriptions of appropriate engineering studies, taking into account the variations in staff expertise and resources among local and state transportation agencies.
 
Consistent application of the improved guidelines should lead to (1) reduced road and lane departures on curves, (2) judicious application of TCDs to promote driver compliance and respect, (3) effective allocation of local and state transportation agencies’ budgets for installing and maintaining TCDs, and (4) a limited level of exposure to tort liability suits.
 
STATUS
 
The Contractor's Draft Report has been received and is available. It is expected that the report will be published as an NCHRP Web-Only Document. The potential MUTCD improvements have been provided to the National Committee on Uniform Traffic Control Devices for their consideration.
 
BACKGROUND
 
In 2002, there were 38,309 fatal crashes on the U.S. highway system and approximately 25% of these crashes occurred on horizontal curves (NCHRP Report 500: Volume 7, A Guide for Reducing Collisions on Horizontal Curves). Traffic control devices (TCDs) such as signs and delineation treatments are intended to inform and warn motorists of horizontal curves and the Manual on Uniform Traffic Control Devices (MUTCD) is the national standard for all TCDs on roads open to public travel. Research has consistently demonstrated that TCDs on curves are inconsistently applied across the United States (NCHRP Report 559: Communicating Changes in Horizontal Alignment) and the 2009 MUTCD provides more prescriptive requirements than previous editions. The intent of this change was to promote uniformity across the country and, thereby, improve safety on horizontal curves. These MUTCD changes have generated much debate because their impacts on safety or driver behavior have not been documented. While transportation agencies support the goal of reducing crashes, there is concern that installing or replacing TCDs on curves may not be the most cost-effective way of improving safety. There is also concern that installing additional TCDs with limited or no benefit “might result in disrespect at those locations where the device is needed and appropriate.” (2009 MUTCD, Section 1A.06)
 
RESEARCH PLAN
 
Task 1. Review Pertinent Literature. The objective of this task is to identify the state of design practice regarding traffic control devices for curves and synthesize the existing information.
 
Task 2. Survey of State Practice. The objective of this task is to identify what policies, standards, or guidelines states follow in determining the traffic control devices that are to be used for horizontal curves.
 
Task 3. Survey of States’ Drivesrs Manuals. The objective of this task is to better understand the information contained in driver manuals and how modifications, based on the research results, might be incorporated to improve driver education and understanding of traffic control devices along curves.
 
Task 4. Conduct Driver Behavior Pilot Testing. The objective of this task is to conduct a pilot test of driver behavior metrics along a winding stretch of rural two-lane highway to better understand how unfamiliar (and familiar) drivers react to various combinations of traffic control devices.
 
Task 5. Determine Feasibility of Conducting Crash-Based Analysis. The objective of this task is to assess the feasibility of conducting a crash-based analysis by developing a draft data collection and analysis plan. This plan includes the study design, identification of study corridors, the procedure for data collection, and the intended data reduction. The plan would be developed in sufficient detail to establish that the execution of the plan will produce the needed results.
 
Task 6. Prepare Phase I Deliverables and Panel Meeting. The objective of this task is to develop and submit an interim report, provide review time, and conduct a panel meeting.
 
Task 7. Conduct Driver Behavior Studies. The objective of this task is to implement the driver behavior data collection and analysis plan tested and refined in Phase I. The purpose of the experiment outlined here is to better understand how unfamiliar drivers use various singular and multiple traffic control devices.
 
Task 8. Conduct Safety Analysis. The objective of this task is to implement the data collection and analysis plan developed in Task 5 and refined by the panel and develop preliminary statistical models for each facility type to relate traffic control devices on curves to crash frequency while accounting for exposure and potential confounding factors.
 
Task 9. Assess Findings from Tasks 7 and 8. The objective of this task is to assess the findings from the driver behavior and safety analysis tasks and use the combined results to identify traffic control performance parameters that will serve as the basis for selecting traffic control recommendations and developing recommended MUTCD language.
 
Task 10. Develop Costs for Treatments. The objective of this task is to compile data on service life cost for the various horizontal curve treatments identified in the literature review, survey of state practices, and treatments evaluated during the course of the project.
 
Task 11. Develop Methodology for Selecting Traffic Control Device Treatments. The objective of this task is to develop a procedure or methodology to be used by a state or local highway official to select from among alternative traffic control devices.
 
Task 12. Develop Deliverables including Guidelines for Traffic Control Devices on Curves. The objective of this task is to develop (1) guidelines for the MUTCD that will be ready for consideration by the NCUTCD and FHWA; (2) supplemental material, as appropriate (e.g., for the ITE’s Traffic Control Devices Handbook); and (3) the project final report. Revise these materials based on panel comments.

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