A roadway departure [1] [2] (also called roadway excursion or run-off-road collision) is a type of incident that occurs when a vehicle leaves the roadway. Such incidents can lead to a single-vehicle collision.
A roadway departure [1] [2] (also called roadway excursion or run-off-road collision) is a type of incident that occurs when a vehicle leaves the roadway. Such incidents can lead to a single-vehicle collision.
Contributing factors can include:
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 roadway departure crashes resulted in 31% of fatal crashes, but were only 16% of all crashes. [4] Roadway departure collisions where the vehicle is sliding or spinning and runs broadside into a fixed obstacle are particularly dangerous since the vehicle doors and sides provide less protection to occupants than the front of the car.
Target fixation is an issue for drivers, causing them to impact with objects that could be easily avoided.
An important concept in understanding roadway departure is the clear zone. This is the roadside area that is free of obstacles and dangerous slopes. Early research at the General Motors Proving Grounds 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 engineers began to try to provide thirty feet of clear, flat ground next to rural highways. 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. [5]
There are several ways to reduce the consequences of roadway departure collisions. They fall into three main categories: preventing excursion 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. [6]
Roadway cross section improvements include high-friction overlays, improving curve banking, and widening shoulders 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.
A relatively inexpensive countermeasure is the placement of a Safety Edge — a 30° compacted taper on the edge of the pavement. This helps any driver that runs off the edge of the roadway to maintain control while trying to steer back onto the pavement. A vertical edge drop-off often results in overcorrection, leading to a head-on collision, rollover, or a run-off-road collision on the far side of the road. Pavement edge drop-offs are problematic on roads where the hard shoulder is narrow or nonexistent. The safety edge adds about 1% to the pavement costs while building or resurfacing a road. [7]
If possible, hazards should be removed, or modified to be less dangerous. Examples include tree removal, using forgiving road infrastructure or extending cross culverts out of the clear zone. Regarding forgiving road infrastructure: standards exist in different countries to crash test road infrastructure and to qualify them as being passive safe or forgiving. In the US there is MASH (the Manual for Assessing Safety Hardware) and in Europe, there is EN12767. Removing obstacles should be the first choice. If that is not possible, make them forgiving. As a last option, isolate the obstacle with a guard rail.
Guard rails are used to reduce the severity of roadway departure crashes by interposing a barrier that is more forgiving to vehicle occupants. The 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%. [8]
Where hazard removal and guard rails reduce the severity of roadway departure crashes, delineation aims to reduce the frequency of crashes by helping drivers stay on the road. It includes pavement markings, object markers, curve warning signs, 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 a guard rail. Signing improvements will generally reduce crashes by about 30%. [8] 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 collisions. 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.
Since most roadway improvements are funded by taxes or user fees, it is important that safety improvements pay for themselves. On low-speed, low-volume local roads, expensive improvements are likely to produce less in savings than they cost, and thus divert scarce resources from locations where they could be better used. On high-speed, high-volume freeways, high-quality clear zones are worth the cost.[ citation needed ]
Traffic engineering is a branch of civil engineering that uses engineering techniques to achieve the safe and efficient movement of people and goods on roadways. It focuses mainly on research for safe and efficient traffic flow, such as road geometry, sidewalks and crosswalks, cycling infrastructure, traffic signs, road surface markings and traffic lights. Traffic engineering deals with the functional part of transportation system, except the infrastructures provided.
Automotive safety is the study and practice of automotive design, construction, equipment and regulation to minimize the occurrence and consequences of traffic collisions involving motor vehicles. Road traffic safety more broadly includes roadway design.
Road traffic safety refers to the methods and measures used to prevent road users from being killed or seriously injured. Typical road users include pedestrians, cyclists, motorists, vehicle passengers, and passengers of on-road public transport.
In road transport, a lane is part of a roadway that is designated to be used by a single line of vehicles to control and guide drivers and reduce traffic conflicts. Most public roads (highways) have at least two lanes, one for traffic in each direction, separated by lane markings. On multilane roadways and busier two-lane roads, lanes are designated with road surface markings. Major highways often have two multi-lane roadways separated by a median.
Rumble strips are a traffic calming feature to alert inattentive drivers of potential danger, by causing a tactile fuzzy vibration and audible rumbling transmitted through the wheels into the vehicle interior. A rumble strip is applied along the direction of travel following an edgeline or centerline, to alert drivers when they drift from their lane. Rumble strips may also be installed in a series across the direction of travel, to warn drivers of a stop or slowdown ahead, or of an approaching danger spot.
A rollover or overturn is a type of vehicle crash in which a vehicle tips over onto its side or roof. Rollovers have a higher fatality rate than other types of vehicle collisions.
A head-on collision is a traffic collision where the front ends of two vehicles such as cars, trains, ships or planes hit each other when travelling in opposite directions, as opposed to a side collision or rear-end collision.
Guard, Guard rails, guardrails, railings or protective guarding, in general, are a boundary feature and may be a means to prevent or deter access to dangerous or off-limits areas while allowing light and visibility in a greater way than a fence. Common shapes are flat, rounded edge, and tubular in horizontal railings, whereas tetraform spear-headed or ball-finialled are most common in vertical railings around homes. Park and garden railings commonly in metalworking feature swirls, leaves, plate metal areas and/or motifs particularly on and beside gates.
A curb, or kerb, is the edge where a raised sidewalk or road median/central reservation meets a street or other roadway.
An impact attenuator, also known as a crash cushion, crash attenuator, or cowboy cushion, is a device intended to reduce the damage to structures, vehicles, and motorists resulting from a motor vehicle collision. Impact attenuators are designed to absorb the colliding vehicle's kinetic energy. They may also be designed to redirect the vehicle away from the hazard or away from roadway machinery and workers. Impact attenuators are usually placed in front of fixed structures near highways, such as gore points, crash barrier introductions, or overpass supports. Temporary versions may be used for road construction projects.
Traffic barriers keep vehicles within their roadway and prevent them from colliding with dangerous obstacles such as boulders, sign supports, trees, bridge abutments, buildings, walls, and large storm drains, or from traversing steep (non-recoverable) slopes or entering deep water. They are also installed within medians of divided highways to prevent errant vehicles from entering the opposing carriageway of traffic and help to reduce head-on collisions. Some of these barriers, designed to be struck from either side, are called median barriers. Traffic barriers can also be used to protect vulnerable areas like school yards, pedestrian zones, and fuel tanks from errant vehicles. In pedestrian zones, like school yards, they also prevent children or other pedestrians from running onto the road.
A collision avoidance system (CAS), also known as a pre-crash system, forward collision warning system (FCW), or collision mitigation system, is an advanced driver-assistance system designed to prevent or reduce the severity of a collision. In its basic form, a forward collision warning system monitors a vehicle's speed, the speed of the vehicle in front of it, and the distance between the vehicles, so that it can provide a warning to the driver if the vehicles get too close, potentially helping to avoid a crash. Various technologies and sensors that are used include radar (all-weather) and sometimes laser (LIDAR) and cameras to detect an imminent crash. GPS sensors can detect fixed dangers such as approaching stop signs through a location database. Pedestrian detection can also be a feature of these types of systems.
The AAA Foundation for Traffic Safety is a non-profit, charitable organization based in Washington, DC, that is dedicated to saving lives through traffic safety research and education. Since its founding in 1947, the AAA Foundation has sponsored over 200 projects related to highway safety, covering topics such as distracted, impaired, and drowsy driving; road rage; graduated driver licensing; driver's education and training; and pedestrian safety. The AAA Foundation research agenda is centered on four priority areas: Driver behavior and performance, emerging technologies, roadway systems and drivers and vulnerable road users.
Road traffic collisions generally fall into one of five common types:
A traffic collision, also known as a motor vehicle collision, or car crash, occurs when a vehicle collides with another vehicle, pedestrian, animal, road debris, or other moving or stationary obstruction, such as a tree, pole or building. Traffic collisions often result in injury, disability, death, and property damage as well as financial costs to both society and the individuals involved. Road transport is statistically the most dangerous situation people deal with on a daily basis, but casualty figures from such incidents attract less media attention than other, less frequent types of tragedy. The commonly used term car accident is increasingly falling out of favor with many government departments and organizations, with the Associated Press style guide recommending caution before using the term. Some collisions are intentional vehicle-ramming attacks, staged crashes, vehicular homicide or vehicular suicide.
The geometric design of roads is the branch of highway engineering concerned with the positioning of the physical elements of the roadway according to standards and constraints. The basic objectives in geometric design are to optimize efficiency and safety while minimizing cost and environmental damage. Geometric design also affects an emerging fifth objective called "livability", which is defined as designing roads to foster broader community goals, including providing access to employment, schools, businesses and residences, accommodate a range of travel modes such as walking, bicycling, transit, and automobiles, and minimizing fuel use, emissions and environmental damage.
Road debris, a form of road hazard, is debris on or off a road. Road debris includes substances, materials, and objects that are foreign to the normal roadway environment. Debris may be produced by vehicular or non-vehicular sources, but in all cases it is considered litter, a form of solid waste. Debris may tend to collect in areas where vehicles do not drive, such as on the edges (shoulder), around traffic islands, and junctions.
Solar road studs are flashing solar cell powered LED low-maintenance lighting devices that delineate road edges and centrelines. Embedded in the road surface, they are an electronic improvement on the traditional cat's eyes and raised pavement marker in that they may give drivers a larger reaction window.
Terminology related to road transport—the transport of passengers or goods on paved routes between places—is diverse, with variation between dialects of English. There may also be regional differences within a single country, and some terms differ based on the side of the road traffic drives on. This glossary is an alphabetical listing of road transport terms.
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