NHTSA data supports that approximately half of all fatal, run-off-road (ROR) crashes occur along curves. While an examination of driver actions is relevant in many of these crashes, it may also be prudent to examine the roadway to understand if proper warnings were in place to notify drivers of the approaching hazard.
In this article, Civil & Traffic Engineering Expert, Richard Tippett discusses required warning signs that are used to notify motorists of curves ahead, the elements considered in determining the necessary signage, and how a forensic investigation can help determine whether signage was proper or in violation of applicable standards.
“Run-Off-Road” Incidents: Requirements for Curve Signage - Expert Overview
Roadways and associated signage are designed to facilitate “driver expectancy,” an industry term that describes a driver’s ability to reliably anticipate approaching conditions. This concept is important in highway engineering because research demonstrates that when drivers’ expectations align with real world conditions, they can more rapidly and successfully respond to hazards within the environment.
Driver expectancy underlines the importance of the Manual on Uniform Traffic Control Devices (MUTCD), which prescribes standardized (uniform) solutions to provide adequate positive guidance for a wide range of traffic situations. Driver’s actions tend to be error free when they receive information they expect, but when conditions and information deviate from those expectations, the instances of driver error increase.
In the context of a run-off-road crash along a curve, investigators may seek to determine if adequate and appropriate signage was provided to aid driver expectancy. The purpose of warning signs is to call attention to an unexpected condition, such as a curve, thus providing the motorist sufficient information and time to adjust their driving.
Were Curve Warning Signs Required?
There are various factors that investigators will consider when reviewing what warning signs are warranted for a particular curve. The MUTCD Sections 2C.06 through 2C.15 cover curve warning signs; however, consideration shall also be given to the state MUTCD Supplement, a state specific MUTCD, and /or other applicable local standards. Curve signage is just one component of the warning/guidance system that may be warranted and proper for a location, with other elements including pavement markings, delineators, and other systemic and site-specific improvements that may also be required.
An evaluation may also include the geometry of the roadway leading to, through, and exiting the subject curve, such as:
- Curve Radius
- Degree of Curvature
- Distance between Curves
- Posted Speed Limit
- Advisory Speed
Depending on the roadway geometry, it may be necessary to utilize alternate and/or incorporate additional and supplemental warning signs that more accurately describe the nature of the curve a driver will face.
The presence of advance curve warning signs (examples shown in Figure 1) may not be the only signs that are required. Some curves require additional signage such as Chevrons or Large Arrow signs placed throughout the length of the curve, based on the difference between the roadway’s prevailing speed and the advisory speed at the curve. Additional measures to address recurring issues are sometimes warranted; such as rumble strips, automatic warning systems to prevent truck rollovers on curved ramps (See Figure 2), and even pavement grooving.
Highway Engineering Investigations
In essence, each curve or set of curves are unique, and the experts at Robson Forensic are experienced with the MUTCD and the correct usage of warning signs. An incident investigation will often include an analysis for compliance or lack of compliance with the applicable standards, and how violations of such standards or lack of response to collision history may be tied to causation of the incident.
The municipal and highway engineers at Robson Forensic are frequently retained to determine if the design, construction, or maintenance operations of roadway systems contributed to the cause of motor vehicle collisions, pedestrian strikes, or other injuries.
Submit an inquiry or call us at 800.813.6736 to discuss your case with an expert.
Civil Engineer & Traffic Engineering Expert
Richard Tippett is a Civil and Traffic Engineer with 30+ years of experience in public works infrastructure projects for roadways, utilities, airports, and building construction. Rick applies his expertise to forensic casework involving civil engineering and the design, construction, and maintenance of roadways and intersections, traffic signalization, municipal engineering, and land development.