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Guard rail, sometimes referred to as guide rail, is a system designed to keep people or vehicles from (in most cases unintentionally) straying into dangerous or off-limits areas. A handrail is less restrictive than a guard rail and provides both support and the protective limitation of a boundary.

Contents 1 Public safety 2 Safety and industry 3 Automotive safety 4 See also

Most public spaces are fitted with guard rails as a means of protection against accidental falls. Any abrupt change in elevation where the higher portion is accessible makes a fall possible. Due to this responsibility and liability, rails are placed to protect people using the premises. Guardrails are generally required by code where there is a drop of 30" or more.

Examples of this are both architectural and environmental. Environmental guard rails are placed along hiking trails where adjacent terrain is steep. Railings may also be located at scenic overlooks.

Guard rails in buildings are numerous, and are required by building codes in many circumstances. Guard rails along stairways are common, and catwalks and balconies are also lined with them.

Building codes also require that no opening in a guard be of a size such that a 4" sphere may pass. There are three exceptions according to the 2003 International Building Code Section 1012.3 which allow openings to not exceed 8" or 21" depending on occupancy groups or special areas.

An architect who was famous for creative use of handrails for social stability was Alvar Aalto. The guard rails of an observation tower such as the Space Needle or Eiffel Tower become exaggerated to the point of becoming a fence or cage. This is also done on bridges and overpasses to prevent accidents and suicides.

In traffic engineering guardrails prevent vehicles from veering off the roadway into oncoming traffic, crashing against solid objects or falling into a ravine. A secondary objective is keeping the vehicle upright while deflected along the guardrail. The problem with this is that a guardrail of the optimum height for a car might not keep a truck from toppling over it, while a motorbike might slip under a higher rail.

In most cases guardrails would not be able to withstand the impact of a vehicle just by the strength of the individual posts in the area hit by the vehicle. Instead, the guardrail is effectively one strong band that transfers the force of the vehicle to multiple posts beyond the impact area or into a ground anchor at the end of the guardrail.

It is important to note that guardrails have frequently ranked as among the highest sources of injury and fatality in a fixed-object crash (1).^{[verification needed]} Among the primary reasons for this is the type of treatment used at the end of the guardrail facing oncoming traffic. Most end designs will either deflect, absorb, or launch the vehicle. Deflection causes the vehicle to be redirected back into traffic -- particularly dangerous on undivided roadways, as the vehicle may travel into oncoming traffic. Absorption is when the force of impact is directly transferred between the vehicle and guardrail, which may cause the end to puncture the vehicle. Lastly, a vehicle can become airborne upon striking a guardrail's end, which may negate the purpose of the guardrail, if the vehicle continues beyond the guardrail and strike with the object the guardrail was protecting. Additionally, an airborne vehicle is likely to collide in a manner that the vehicle was not designed for, increasing the risk of failure in the vehicle's collision safety systems. Collapsible guard rails are safer than rigid ones, since a longer collision duration will result in a smaller average impact force.

Transportation engineers are increasingly limiting the use of guardrail as much as possible, as guardrails should only be placed when the roadside conditions pose a greater threat than the guardrail itself. In addition to new research into end treatments, public awareness among both drivers and engineers has been gradually reducing injuries and fatalities due to guardrails.

Guardrails are also incorporated beneath the sides of high-sided heavy vehicles such as lorries. This is in order to prevent smaller vehicles (e.g. cars) from passing between the lorry's front and rear wheels during a collision and being crushed by the lorry's rear wheels.

• Crash barrier