Run-off-road collision
Encyclopedia
A run-off-road collision is a type of single-vehicle accident
that occurs when a vehicle leaves the roadway. Contributing factors often include loss of control or mis-judging a curve, or attempting to avoid colliding with another road user or an animal. If the vehicle strikes a fixed object (an object that will move very little when struck, such as a tree, bridge structure or utility pole) or rolls over
, the crash is likely to result in injuries or fatalities. 2005 statistics from the US show that run off road crashes resulted in 31% of fatal crashes, but were only 16% of all crashes.
found that 80% of their test drivers stopped or regained vehicle control within 30 feet (9 m) of the edge of the travel lane. As a result, civil engineer
s began to try to provide thirty feet of clear, flat ground next to rural highway
s. The result was fewer crashes. Current guidance adjusts the desired clear zone width for curvature, roadside slope, speed and volume. More width is recommended on the outsides of curves, where the ground slopes down away from the road, and on high speed, high volume roads.
s or travel lanes. The intention is to help the driver to keep the car on the roadway. They are usually expensive unless included in a highway reconstruction project.
Guard rail
is used to reduce the severity of run-off-road crashes by interposing a barrier that is more forgiving to vehicle occupants. It is important to note that guard rail is itself a hazard and should only be used where it shields traffic from a hazard that is more dangerous than it is. It may not reduce the number of run-off-road crashes, since it is longer and closer to the road than the hazard behind it. Properly designed and installed, it will reduce the severity of crashes that do occur. One study found that installing guard rail above an embankment would only reduce run-off-road crashes by only 7%. However, injury and fatal crashes were reduced by 45%.
s, delineators, and arrows and chevrons on curves. It is used where other improvements would be too costly or ineffective, as an interim method until other improvements can be installed, and to help drivers avoid collisions with guarderail. Signing improvements will generally reduce crashes by about 30%. Because of its low cost, delineation is often the measure of choice on lower volume roads.
Some of these measures can also reduce the frequency and severity of head-on collision
s. Median barriers are a form of guard rail that turn head-on crashes into fixed object crashes. Curve delineation and cross-section improvements can reduce loss-of-control incidents.
Single-vehicle accident
A single vehicle collision or single-vehicle accident is, as the name implies, a type of road traffic accident in which only one vehicle is involved...
that occurs when a vehicle leaves the roadway. Contributing factors often include loss of control or mis-judging a curve, or attempting to avoid colliding with another road user or an animal. If the vehicle strikes a fixed object (an object that will move very little when struck, such as a tree, bridge structure or utility pole) or rolls over
Rollover
A rollover is a type of vehicle accident in which a vehicle tips over onto its side or roof. The most common cause of a rollover is traveling too fast while turning.- Dynamics :Vehicles can roll over in several ways...
, the crash is likely to result in injuries or fatalities. 2005 statistics from the US show that run off road crashes resulted in 31% of fatal crashes, but were only 16% of all crashes.
Clear zones
An important concept in understanding run-off-road crashes is the clear zone. This is the roadside area that is free from obstacles and dangerous slopes. Early research at the General Motors Proving GroundsGeneral Motors Proving Grounds
-Desert Proving Ground Yuma:Desert Proving Ground Yuma is a facility co-built and leased by General Motors located within the US Army's Yuma Proving Grounds. The site contains a inner facility sitting on 2,400 acres with a 24 acre campus containing 98,000 ft2 of building area and also has 40 miles...
found that 80% of their test drivers stopped or regained vehicle control within 30 feet (9 m) of the edge of the travel lane. As a result, civil engineer
Civil engineer
A civil engineer is a person who practices civil engineering; the application of planning, designing, constructing, maintaining, and operating infrastructures while protecting the public and environmental health, as well as improving existing infrastructures that have been neglected.Originally, a...
s began to try to provide thirty feet of clear, flat ground next to rural highway
Highway
A highway is any public road. In American English, the term is common and almost always designates major roads. In British English, the term designates any road open to the public. Any interconnected set of highways can be variously referred to as a "highway system", a "highway network", or a...
s. The result was fewer crashes. Current guidance adjusts the desired clear zone width for curvature, roadside slope, speed and volume. More width is recommended on the outsides of curves, where the ground slopes down away from the road, and on high speed, high volume roads.
Prevention and mitigation
There are several ways to reduce consequences of run-off-road collisions. They fall into three main categories: preventing run-off-road incidents, minimizing the likelihood of a crash or roll-over if the vehicle travels off the shoulder, and reducing the severity of those that do occur.Roadway cross section improvements
Roadway cross section improvements include high friction overlays, improving curve banking, and widening shoulderShoulder (road)
A hard shoulder, or simply shoulder, is a reserved area by the verge of a road or motorway. Generally it is kept clear of motor vehicle traffic...
s or travel lanes. The intention is to help the driver to keep the car on the roadway. They are usually expensive unless included in a highway reconstruction project.
Hazard removal or modification
If possible, hazards should be removed, or modified to be less dangerous. Examples include tree removal, or extending cross culverts out of the clear zone. Where costs and right-of way allow it, this should be the first choice. However, many local roads have narrow rights of way, and clear zone improvements may require right-of-way takings or easements. This may not be cost-effective on low to medium volume rural roads.Guard rail
Guard rail
Guard rail or guardrail, sometimes referred to as guide rail or railing, is a system designed to keep people or vehicles from straying into dangerous or off-limits areas...
is used to reduce the severity of run-off-road crashes by interposing a barrier that is more forgiving to vehicle occupants. It is important to note that guard rail is itself a hazard and should only be used where it shields traffic from a hazard that is more dangerous than it is. It may not reduce the number of run-off-road crashes, since it is longer and closer to the road than the hazard behind it. Properly designed and installed, it will reduce the severity of crashes that do occur. One study found that installing guard rail above an embankment would only reduce run-off-road crashes by only 7%. However, injury and fatal crashes were reduced by 45%.
Delineation
Where hazard removal and guardrail reduce the severity of run-off-road crashes, delineation aims to reduce the frequency of crashes by helping drivers stay on the road. It includes pavement markings, object markers, curve warning signWarning sign
A traffic warning sign is a type of traffic sign that indicates a hazard ahead on the road that may not be readily apparent to a driver.In most countries, they usually take the shape of an equilateral triangle with a white background and a thick red border...
s, delineators, and arrows and chevrons on curves. It is used where other improvements would be too costly or ineffective, as an interim method until other improvements can be installed, and to help drivers avoid collisions with guarderail. Signing improvements will generally reduce crashes by about 30%. Because of its low cost, delineation is often the measure of choice on lower volume roads.
Some of these measures can also reduce the frequency and severity of head-on collision
Head-on collision
A head-on collision is one where the front ends of two ships, trains, planes or vehicles hit each other, as opposed to a side collision or rear-end collision.-Rail transport:...
s. Median barriers are a form of guard rail that turn head-on crashes into fixed object crashes. Curve delineation and cross-section improvements can reduce loss-of-control incidents.