Product Code Database
Traffic barriers (known in North America as guardrails or , in Britain as crash barriers, and in auto racing as Armco barriersAK Steel (formerly Armco) genericized trademark) keep within their roadway and prevent them from colliding with dangerous such as boulders, sign supports, trees, bridge abutments, buildings, walls, and large , or from traversing steep (non-recoverable) slopes or entering deep water. They are also installed within road median 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, , and fuel tanks from errant vehicles. In pedestrian zones, like school yards, they also prevent children or other pedestrians from running onto the road.
While barriers are normally designed to minimize injury to vehicle occupants, injuries do occur in collisions with traffic barriers. They should only be installed where a collision with the barrier is likely to be less severe than a collision with the hazard behind it. Where possible, it is preferable to remove, relocate or modify a hazard, rather than shield it with a barrier.
To make sure they are safe and effective, traffic barriers undergo extensive crash simulation and full scale before they are approved for general use. While crash testing cannot replicate every potential manner of impact, testing programs are designed to determine the performance limits of traffic barriers and provide an adequate level of protection to road users.
Clear zone, also known as clear recovery area or horizontal clearance is defined (through study) as a lateral distance in which a motorist on a recoverable slope may travel outside of the travelway and return their vehicle safely to the roadway. This distance is commonly determined as the 85th percentile in a study comparable to the method of determining speed limits on roadways through speed studies and varies based on the classification of a roadway. In order to provide for adequate safety in roadside conditions, hazardous elements such as fixed obstacles or steep slopes can be placed outside of the clear zone in order to reduce or eliminate the need for roadside protection.
Common sites for installation of traffic barrier:
When a barrier is needed, careful calculations are completed to determine length of need. The calculations take into account the speed and volume of traffic volume using the road, the distance from the edge of travelway to the hazard, and the distance or offset from the edge of travelway to the barrier.
The regulation highlights the importance of designing and implementing barriers that are robust enough to withstand various threat scenarios, including different types of vehicles and potential . The integration of these barriers with other security measures, such as surveillance, access control, and intrusion detection systems, forms a critical component of comprehensive security planning at nuclear facilities. The NRC's detailed guidelines on vehicle barriers demonstrate its commitment to maintaining high standards of safety and security at U.S. nuclear sites. Adherence to these regulations is crucial for mitigating risks associated with vehicle-based threats. ecfr.gov
are used to prevent vehicles from crossing over a median and striking an oncoming vehicle in a head-on crash. Unlike roadside barriers, they must be designed to be struck from either side.
are designed to restrain vehicles from crashing off the side of a bridge and falling onto the roadway, river or railroad below. It is usually higher than roadside barrier, to prevent trucks, buses, pedestrians and cyclists from vaulting or rolling over the barrier and falling over the side of the structure. Bridge rails are usually multi-rail tubular steel barriers or reinforced concrete parapets and barriers.
are used to protect traffic from hazards in work zones. Their distinguishing feature is they can be relocated as conditions change in the road works. Two common types are used: temporary concrete barrier and water-filled barrier. The latter is composed of steel-reinforced plastic boxes that are put in place where needed, linked together to form a longitudinal barrier, then ballasted with water. These have an advantage in that they can be assembled without heavy lifting equipment, but they cannot be used in freezing weather.
are used to enhance security by preventing unauthorized or hostile vehicles from entering sensitive or protected locations, such as government buildings, military installations, airports, embassies, and high-security facilities. They act as a formidable deterrent against potential threats, including vehicle-borne attacks and unauthorized access. Road blockers are equipped with mechanisms that allow for quick deployment and retraction when needed, providing a flexible and effective means of traffic control and security management.
, Platform screen doors (PSDs) without the doors, are used when PSDs are not feasible due to cost, technological compatibility or other factors.
include cable barriers and weak post corrugated guide rail systems. These are referred to as flexible barriers because they will deflect when struck by a typical passenger car or light truck. Impact energy is dissipated through tension in the rail elements, deformation of the rail elements, posts, soil and vehicle bodywork, and friction between the rail and vehicle.
include box beam guide rail, heavy post blocked out corrugated guide rail and thrie-beam guide rail. Thrie-beam is similar to corrugated rail, but it has three ridges instead of two. They deflect : more than rigid barriers, but less than flexible barriers. Impact energy is dissipated through deformation of the rail elements, posts, soil and vehicle bodywork, and friction between the rail and vehicle. Box beam systems also spread the impact force over a number of posts due to the stiffness of the steel tube.
are usually constructed of reinforced concrete. A permanent concrete barrier will only deflect a negligible amount when struck by a vehicle. Instead, the shape of a concrete barrier is designed to redirect a vehicle into a path parallel to the barrier. This means they can be used to protect traffic from hazards very close behind the barrier, and generally require very little maintenance. Impact energy is dissipated through redirection and deformation of the vehicle itself. Jersey barriers and also lift the vehicle as the tires ride up on the angled lower section. For low-speed or low-angle impacts on these barriers, that may be sufficient to redirect the vehicle without damaging the bodywork. The disadvantage is there is a higher likelihood of rollover with a small car than the single slope or step barriers. "Frequently Asked Questions: Barriers, Terminals, Transitions, Attenuators, and Bridge Railings", Federal Highway Administration. Access date 2/15/2011. Impact forces are resisted by a combination of the rigidity and mass of the barrier. Deflection is usually negligible.
An early concrete barrier design was developed by the New Jersey State Highway Department. This led to the term Jersey barrier being used as a generic term, although technically it applies to a specific shape of concrete barrier. Other types include constant-slope barriers, concrete step barriers, and .
Concrete barriers usually have smooth finishes. At some impact angles, coarse finishes allow the drive wheel of front wheel drive vehicles to climb the barrier, potentially causing the vehicle to roll over. However, along and other areas where aesthetics are considered important, reinforced concrete walls with stone veneers or faux stone finishes are sometimes used. These barrier walls usually have vertical faces to prevent vehicles from climbing the barrier.
In response, a new style of barrier terminals was developed in the 1960s in which the installers were directed to twist the guardrail 90 degrees and bring its end down so that it would lie flat at ground level (so-called "turned-down" terminals or "ramped ends"). While this innovation prevented the rail from penetrating the vehicle, it could also vault a vehicle into the air or cause it to roll over, since the rising and twisting guardrail formed a ramp. These crashes often led to vehicles vaulting, rolling, or vaulting and rolling at high speed into the very objects which guardrails or barriers were supposed to protect them from in the first place. Such wild crashes caused the United States to ban ramped ends in 1990 on high-speed, high-volume highways, and to extend the ban in 1998 to the entire National Highway System. (2025). 9780203881200, CRC Press. ISBN 9780203881200
To address the vaulting and rollover crashes, a new type of terminals were developed. The first generation of these terminals in the 1970s were breakaway cable terminals, in which the rail curves back on itself and is connected to a cable that runs between the first and second posts (which are often breakaway posts). These barrier terminals were sometimes able to spear through small cars that hit them at exactly the wrong angle and were deprecated in 1993. The second generation of these terminals, called energy-absorbing terminals, was developed in the 1990s and 2000s. The goal was to develop a kinetic energy dissipating system soft enough for small vehicles to decelerate without causing the guardrail to spear through them, but firm enough to stop larger vehicles. The energy dissipation could be done through bending, kinking, crushing, or deforming guardrail elements. The first family of energy-absorbing terminal products was the extruding terminal type. It features a large steel impact head that engages the frame or bumper of the vehicle in head-on collisions. The impact head is driven back along the guide rail, dissipating the vehicle's kinetic energy by bending or tearing the steel in the guide rail sections away to the side to prevent spearing. When the terminals are hit in an angle, they dissipate much of the energy but the "gating" feature allows the vehicles to pass through the rail as it bends.
If space allows, a guide rail may also be terminated by gradually curving it back to the point that the terminal is unlikely to be hit end-on, or, if possible, by embedding the end in a hillside or cut slope.
An alternative to energy absorbing barrier terminals are impact attenuators. These are used for wider hazards that cannot be effectively protected with a one-sided traffic barrier.
Tire recycling had been proposed for highway crash barriers by 2012, but many governments prefer sand-filled crash barriers because they have excellent energy-absorption characteristics and are easier to erect and dismantle.
A Fitch barrier is an energy-absorbing type of impact attenuator consisting of a group of sand-filled plastic barrels, usually yellow in color with a black lid. Fitch barriers are often found in a triangular arrangement at the end of a guard rail between a highway and an exit lane (the area known as the gore), along the most probable line of impact. The barriers in front contain the least sand, with each successive barrel containing more. When a vehicle collides with the barrels, the vehicle's kinetic energy is dissipated by the shattering of the barrels and the scattering of the sand inside, and the vehicle decelerates over a longer period of time instead of sudden and more violent rapid deceleration from striking a solid obstruction. In turn, the risk of injury to the vehicle occupants is greatly reduced. Fitch barriers are widely popular due to their effectiveness, low cost, and ease of setup and repair or replacement.
Types of end treatments:
See also
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