Run-Off-Road Collisions

Introduction

The American Association of State Highway and Transportation Officials's (AASHTO's) Strategic Highway Safety Plan identified 22 goals to pursue in order to significantly reduce highway crash fatalities. One of the plan's hallmarks is to comprehensively approach safety problems. Goal 15 in the Strategic Highway Safety Plan is Keeping Vehicles on the Roadway, and Goal 16 is Minimizing the Consequences of Leaving the Road. Subsequently, three emphasis areas evolved from these two goals:

  • Run-off-road (ROR) crashes,
  • Head-on crashes, and
  • Crashes with trees in hazardous locations.

The common solution to these goal areas is to keep the vehicle in the proper lane. While this may not eliminate crashes with other vehicles, pedestrians, bicyclists, or trains, it would eliminate many fatalities that result when a vehicle strays from the lane onto the roadside or into oncoming traffic.

This emphasis area deals with ROR crashes associated with vehicles that leave the travel lane, encroach onto the shoulder and beyond, and hit one or more of any number of natural or artificial objects, such as bridge walls, poles, embankments, guardrails, parked vehicles, or trees. (Because trees are the most abundant objects along the road, they are treated as a separate emphasis area.)

ROR crashes usually involve only a single vehicle, although a ROR vehicle hitting a parked vehicle could be considered a multivehicle crash. A ROR crash, which consists of a vehicle encroaching onto the right shoulder and roadside, can also occur on the median side where the highway is separated or on the opposite side when the vehicle crosses the opposing lanes of a nondivided highway.

Reducing the likelihood that a vehicle will leave the roadway through roadway design (e.g., flattening curves or installing shoulder rumble strips) can prevent deaths and injuries resulting from ROR crashes. When an errant vehicle does encroach on the roadside, fatalities and injuries can be reduced if an agency can either (a) minimize the likelihood of the vehicle crashing into an object (e.g., through object removal or relocation) or overturning (e.g., through sideslope flattening or improved ditch design) or (b) reduce the severity of the crash (e.g., installing breakaway devices).

AASHTO's overall goal is to move away from independent activities of engineers, law enforcement, educators, judges, and other highway safety specialists and toward coordinated efforts. The implementation process outlined in the guides promotes forming working groups and alliances that represent all of the elements of the safety system. In this formation, highway safety specialists can draw upon their combined expertise to reach the bottom-line goal of targeted reduction of crashes and fatalities associated with a particular emphasis area.