Engineering:Guard rail

Guard rail, guardrails — or railings around properties and more generally outside of North America in some uses overlaps the industrial term "guide rail". They 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.

High security railings (particularly if in flat metal then a type of palisade) may instead feature jagged points and most metals are well-suited to anti-climb paint.

A handrail is less restrictive on its own than a guard rail and provides support.

Public safety

Sign in Niagara Falls, Ontario, warning people not to climb over guard rail overlooking the Niagara River.

A handrail leading along a rocky creek crossing

A crowd barrier (guard rail — North America) collapses at a college football game, spilling fans onto the sidelines.

A cast iron grille of decorative railings interspersed by weighty columns in St Petersburg

Many 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 in the US are generally required by code where there is a drop of 30 inches (0.76 m) 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 can be numerous, and are required by building codes in many circumstances. Handrails along stairways are common known as a balustrade where filled out below, and catwalks (a type of footbridge) and balconies are also lined with them. An example of a common residential guard rail (US) handrail (Brit.) is a wood railing around a deck or patio. In the US this is typically built on-site from pressure treated lumber thus featuring a simplistic design of vertical baluster spaced every 3.5" demonstrating compliance with Building Codes (Standards).

Cable railings typically use stainless steel cables strung horizontally. Glass balusters and glass panels open the view while still providing safety, as at the Grand Canyon Skywalk. With the increasing popularity of composite lumber for decking, manufacturers, like TimberTech are providing composite railing components. Wrought iron is another choice that is traditional and sturdy. Decorative examples are considered ironwork.

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.

A major architect imaginitively used handrails representing social stability, 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.

Facility safety guardrail

Guardrail protecting expensive machinery

Guardrails are used in a facility setting to protect a company's greatest assets which include their people and expensive equipment.

In the US, under OSHA Standard 1910.28(b)(15), employees who work on surfaces that are 4 feet (1.2 m) or higher off of the ground must have personal fall protection systems in place, such as handrails or guardrails.

The strongest options are of industrial strength such as 4" Schedule 80, 6" Schedule 40 metal sleeved in Hi-Density Thermoplastic Polyethylene (thus maintenance-free). They will be mounted using a base-plate or cored into cement to enhance the strength.

Guardrail can also be constructed of 10 gauge high-tensile steel formed into a two-rib corrugated design with two secondary ribs. This guardrail is similar in appearance to guardrails in an outdoor setting, but is often used in facilities. Once it is impacted, it must be repaired and replaced.

Germany first patented strong guardrails. Guardrails, metallic corrosion-resistant high-security guardrails developed in the US, prevented the loss of life of tens of thousands. Several international standards have been developed for the production and installation of guardrails, such as EN1317, RAL, and RC6120.

Automotive safety

Further information: Engineering:Traffic barrier

A truck crashed through the central barrier of a German freeway (A24).

A removable guardrail as median barrier

In traffic engineering, highway guardrail may prevent an errant vehicle from hitting roadside obstacles which may be either man-made (sign structures, culvert inlets, utility poles) or natural (trees, rock croppings), running off the road and going down a steep embankment, or veering off the roadway into oncoming traffic (commonly referred to as a median barrier). Roadside obstacles are typically referred to as fixed objects. A secondary objective is keeping the vehicle upright while deflected along the guardrail. Variables such as motorist speed and vehicle orientation when striking the guardrail are crucial factors in the effectiveness of guardrail performance.

The most common type of guardrail in use today is the Blocked-Out W-beam (Strong Post). Strong-post W-beam guardrail consists of wood posts and wood blockouts or steel posts with wood or plastic blockouts. The wood or plastic blockouts reduce or minimize a vehicle snagging on the posts upon impact. In addition, a blockout may be used to increase the offset of guardrail with an obstacle such as a curb.The posts' primary purpose is to maintain the height of the guardrail during the initial stages of post deflection. Maintaining guardrail height also reduces the potential for a vehicle to vault over the guardrail upon initial impact.

The posts also play a role in the amount of resistance and deflection a guardrail may experience during impact. Resistance in a strong post system results from a combination of tensile and flexural stiffness of the rail and the bending and shearing resistance of the posts.

One of the main concerns with strong-post W-beam guardrail has been the ability of the system to contain and redirect modern vehicles that have a higher center of gravity along with the increased weight of those vehicles. 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. To address these concerns, significant research and development of a system that could contain and redirect vehicles of varying weights and heights was developed and crash tested (both controlled and simulated). As a result, the Midwest Guardrail System (MGS) was developed and successfully crash tested per NCHRP Report 350 TL-3 criteria. MGS has a higher mounting height, uses larger posts and blockouts as compared to the strong-post W-beam guardrail. One other significant difference is that MGS rail splices occur at mid-span compared to at the posts like the strong-post w-beam guardrail.

In most cases, guardrail 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. Guardrail functions as a system with the guardrail, posts, connection of the rail to the posts and to each other, and the end anchors (or terminals) all playing an integral role in how the guardrail will function upon impact. Soil conditions, height of rail, presence of curb or dike, weight of impacting vehicle, distance from back of post to hinge point and depth of post within soil can all determine how well the system will function upon impact.

Guardrail is effectively one strong band that transfers the force of the vehicle to the rail elements, posts, and end terminals or anchors A run of guardrail must be anchored at each terminating end either by transitioning the rail into a fixed anchor such as a bridge rail or with an end terminal or end anchor placed in the ground or within an embankment. Newer concrete barriers, while usually strong enough to withstand direct hits by cars, still work on a similar principle in deflecting heavier vehicles such as trucks.

Though they have usually prevented far more serious accidents, guardrail is considered a roadside obstacle as well and transportation engineers must weigh whether placing guardrail will reduce the severity of an impact as compared to what may be impacted if the guardrail were not placed. In general, the minimum length of guardrail with an end anchor at the trailing end and an end terminal on the approach end will be 62.5 to 75 feet in length. An example would be where an overhead roadside sign structure is placed within what is considered the clear recovery zone — An engineer would need to determine that the structure has a potential to be impacted and the impact of a vehicle with that structure would be much more severe than impacting the guardrail.

Guardrail has frequently ranked amongst the highest sources of injury and fatality collisions with a fixed-object crash. Among the primary reasons for this is the type of treatment used at the end of the guardrail facing oncoming traffic. Most end terminal designs will either gate and allow a vehicle to pass through the system within the first 12.5 feet or redirect a vehicle if impacted beyond the first 12.5 feet. Some end terminals also have energy absorbing properties when impacted in the head on position, and will actually slow a vehicle upon impact by absorbing the vehicles kinetic energy and dispersing it through the rail. This is typically accomplished by forcing rail elements through an extrusion impact head that has smaller dimensions that the rail being forced through it. The force rate and flattening of the rail through the head absorbs kinetic energy dissipating it through the extrusion head and slowing the vehicle. These types of systems have demonstrated that an errant vehicle, impacting a system in the head on position, can be effectively stopped in a distance of 50 feet or less. As compared to non-energy absorbing end terminals which can allow a vehicle to pass through the system and travel in excess of 250 feet behind and beyond the system.

Guardrail is intended to deflect. The amount of deflection is dependent on a number of factors some of which include type and weight of impacting vehicle, height the guardrail is placed, type of soil the posts may be embedded within, length of embeddment of the posts, and distance of the hinge point to the face of guardrail are just a few. A guardrail that deflects significantly can causes pocketing which has the potential to snag a vehicle which may cause it to flip or rollroll, or cause the rail to fail allowing a vehicle to penetrate the guardrail.

Modern installations of guardrail are designed to allow the guiderail to deform under the load of the crash, and safely redirecting a vehicle back onto the roadway at a somewhat shallow angle. It is important that the approach grades to a guardrail system be very flat (typically 10:1 or flatter) and that grades and fixed objects behind guardrail be placed at a distance so that it will not affect the performance of the guardrail upon impact and deflection.

Absorption is when the force of impact is directly transferred between the vehicle and guardrail, which may cause the end to puncture the vehicle. This is most common where a "whale tail" or blunt end treatment exists. To mitigate this a number of guiderail end treatments exist such as "Extruder end treatments", "eccentric loaders" and "Driveway wrap treatments" which result in blunt ends rarely being left exposed in modern installations.

Lastly, a vehicle can become airborne upon striking a guardrail with a buried end treatment if the slope to which the end anchor is buried is relatively flat (3:1 or flatter), which may negate the purpose of the guardrail, if the vehicle continues beyond the guardrail and strikes 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. Guardrail will have some give and deflection upon impact. The amount of deflection depends on many factors of which speed and weight of vehicle, type of guardrail installed, height of rail, length of posts, soil conditions and a number of other factors can all play a role. Guardrail must be installed so that it is not so rigid that the rail will fail upon impact or the posts will snap off at the point where they are embedded within the ground.

Transportation engineers limit the amount of guardrail placed as much as possible, as guardrails should only be placed when the roadside conditions pose a greater threat than the guardrail itself. In fact, in the hierarchy of five roadside safety treatments, shielding with guardrails ranks fourth. Therefore, while guardrails are often added as a retrofit to existing roads, newer roads are designed to minimize roadside obstacles, whether that may include aligning a road on a smoother curve or filling in a ravine which would eliminate the need for guardrail altogether. 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.

There are four general types of guardrail, ranging from weakest and inexpensive to strongest and expensive; cable and wood posts, steel and wood/metal posts, steel box-beam, and concrete barriers. While cheaper guardrail is the weakest, often being destroyed from the impact of a light vehicle, it is inexpensive and quick to repair, so this is frequently used in low-traffic rural areas. On the other hand, concrete barriers can usually withstand direct hits from a larger variety of vehicle types, making them well suited for use on high volume routes such as freeways. While rarely damaged, they would be considerably more expensive and time-consuming to repair. Concrete barriers are frequently installed in the median, being expected to withstand frequent impacts from both sides, while the shoulders of the road often have cheaper guardrail. Although the use of concrete barriers on the right side of highway is becoming a much for frequent occurrence in areas where guardrail may be sustaining frequent impacts and the ability for maintenance repairs may be restricted by the general area or work windows due to high traffic volumes for most of the day.

Traffic dangers

In cities occasionally pedestrian railings (and barriers) are installed at the immediate side of a roads however cyclists have died when crushed against them by motor vehicles. Close "safety barriers" to roads have been found to increase the chances of injury to pedestrians for a number of reasons including increasing inattention of drivers and pedestrians. For these reasons some councils in the United Kingdom have removed their pedestrian railings. This was after London's Royal Borough of Kensington and Chelsea did so and found that the rate of injury to pedestrians decreased three times faster than elsewhere in the city.

The removal of barriers divorcing wheeled traffic from pedestrians is an essential of the shared space paradigm and philosophy in urban design. Security barriers have been introduced on a number of the world's major bridges and around key areas of congregation.

Railways

Railway trackage has guard rails (aka check rails) to guide wheels through possible catch points on turnouts or diamonds. Similarly, guard rails may be installed inside the innermost running rails on very sharp curves. The other most common usage is to prevent damage to other structures, especially bridges, in a derailment.

See also

• Cable railings
• Baluster
• Bollard
• Cable barrier
• Concrete step barrier
• Handrail
• Parapet
• Jersey barrier
• Traffic barrier
• Traffic cone
• Ironwork

External links

• Roadside Hardware Policy and Guidance – United States Federal Highway Administration
• Glass Railing Building Codes