Wheel chock

Wheel chocks (or chocks) are wedges of sturdy material placed closely against a vehicle's wheels to prevent accidental movement. Chocks are placed for safety in addition to setting the brakes. The bottom surface is sometimes coated in rubber to enhance grip with the ground. For ease of removal, a rope may be tied to the chock or a set of two chocks. One edge of the wedge has a concave profile to contour to the wheel and increase the force necessary to overrun the chock. Most commonly, chocks are seen on aircraft and train cars.

Automobiles usually have parking brakes on the rear wheels. If the rear axle is jacked off the ground with only the parking brake set, the vehicle may roll on the front wheels and fall. Chocking the front wheels prevents this mishap. Motorcycle and bicycle chocks are bifurcated and fit around the wheel, supporting the bike and preventing its movement.

The mining industry uses wheel chocks to protect lubrication trucks and heavy maintenance vehicles from slipping on off-road terrain when placed in Park. The huge haul trucks, which can weigh up to 450 tonnes, require a much larger wheel chock that itself will weigh almost 40 kilograms. These circumstances will benefit from urethane wheel chocks that are lightweight enough to be maneuvered, yet can withstand the responsibility of holding a truck if a brake should fail. The Mine Safety and Health Administration (MSHA) has established standards that wheel chocks are used when a vehicle is parked on a grade, and OSHA has guidelines that require wheel chocks during loading or unloading of a heavy truck.


Wheel chocks placed around an aircraft's landing gear.

Airbus A321-231 - British Airways - G-EUXH - EHAM (2)

Chocks being fitted to a British Airways Airbus A321.

F-117 Nighthawk fighter during an end of runway check

An airman prepares to pull the landing gear wheel chock of an F-117 Nighthawk fighter during an end of runway check at Kunsan Air Base, South Korea.


A sign telling truck drivers to chock their wheels.

How to use wheel chocks

To use, wheel chocks must be selected to match the size of the tires on the vehicle and used in pairs, as the size of the tire is designed to be proportional to the vehicle's weight and size.

Chock height required = Grade × the diameter of the wheel. For example if the grade is 20% then the chock required is 20% the height of the wheel so long as the chock can support the mass of the wheel. For cable drums that only sit on grades of 5% or less than the chock height would only need to be 5% of the height of the cable drum. For vehicles a chock between 20% and 25% of the height of the wheel should be used.

Three main factors affect the performance of wheel chocks:

  1. The angle of the road surface, called slope or grade. Parking on an angle greater than 10 degrees increases the risk of the car rolling off or over the chock.
  2. The size (height) of the wheel chock compared to the wheel height. Extra large wheel chocks are suitable for e.g. parked air craft where wind forces may come into effect.
  3. The surface slip or friction of the road surface, as the wheel chock may slide downhill due to wet grass or ice. Increasing the size of the wheel chock will not necessary allow the parking on inclines greater than 30% gradient (16.6 degrees).

Wheel chocks must be used on a level surface; some rubber wheel chocks have steel grates and ice cleat accessories. The vehicle is placed in park (on vehicles with automatic gearboxes) and the parking or emergency brake is applied. The wheel chocks are then snugly positioned against the center of the tires in the direction of the grade, on both the left and right side of the vehicle. On even surfaces, chocks are applied to the rear-facing as well as the front-facing side of each tire.

Parking chocks

A parking space commonly contains a parking chock, a barrier which is used to prevent cars from pulling too far into the space and obstructing an adjacent parking space, curb, or sidewalk.

This barrier, also called a parking stop or a turtarrier, is usually made of concrete or recycled plastic and will normally be a horizontal bar to prevent the tires from moving forward or a vertical bar that may cause damage to the vehicle if contact is made. In a parking garage, the barrier will often be a concrete wall. The recycled plastic parking stops are more lightweight than concrete and will not crack or chip. This lighter version can be installed by one person and will resist auto oils and fuels and will never need maintenance such as repainting.

External links


Chock may refer to:

Chock (surname)

Chock (TV series), a Swedish horror television series

Chock, a Swedish-language edition of Chill (role-playing game)Devices for preventing movement:

Wheel chock

Chock (climbing), anchor

Chock, component of a sailing block

Classification yard

A classification yard (American and Canadian English) or marshalling yard (British, Hong Kong, Indian, Australian and Canadian English) is a railway yard found at some freight train stations, used to separate railway cars onto one of several tracks. First the cars are taken to a track, sometimes called a lead or a drill. From there the cars are sent through a series of switches called a ladder onto the classification tracks. Larger yards tend to put the lead on an artificially built hill called a hump to use the force of gravity to propel the cars through the ladder.

Freight trains that consist of isolated cars must be made into trains and divided according to their destinations. Thus the cars must be shunted several times along their route in contrast to a unit train, which carries, for example, cars from the plant to a port, or coal from a mine to the power plant. This shunting is done partly at the starting and final destinations and partly (for long-distance-hauling) in classification yards.

Glossary of North American railway terms

This page contains a list of terms, jargon, and slang used to varying degrees by railfans and railroad employees in the United States and Canada. Although not exhaustive, many of the entries in this list appear from time to time in specialist, rail-related publications. Inclusion of a term in this list does not necessarily imply its universal adoption by all railfans and railroad employees, and there may be significant regional variation in usage.

Piedmont Triad International Airport

Piedmont Triad International Airport (IATA: GSO, ICAO: KGSO, FAA LID: GSO) (commonly referred to as "PTI") is an airport located in the center of North Carolina just west of Greensboro, serving the Piedmont Triad region of Greensboro, High Point and Winston-Salem as well as the entire Piedmont Triad region in North Carolina. The airport, located just off Bryan Boulevard, sits on a 3,770 acre (1,526 ha) campus and has 3 runways. Piedmont Triad International airport is the third busiest airport in North Carolina averaging 280 takeoffs and landings each day. PTI is owned and operated by the Piedmont Triad Airport Authority.

This airport is included in the National Plan of Integrated Airport Systems for 2011–2015, which categorized it as a primary commercial service airport since it has over 10,000 passenger boardings (enplanements) per year.A proposal to rename the airport to "Central North Carolina International Airport" passed in December 2017; the renaming was slated to become effective on January 1, 2018. Due to public objections, however, the name change is on hold.

Tampines MRT station

Tampines MRT station (EW2/DT32) is a Mass Rapid Transit (MRT) interchange station on the Downtown line and East West line in Tampines, Singapore. Located at the heart of the Tampines Town Centre, Tampines station is within the close proximity of Tampines Bus Interchange and the new Tampines Concourse Bus Interchange.

The East West Line station is not linked to the Downtown line’s, hence, passengers are required to exit the former station in order to enter the latter station, or vice versa. It is considered a "valid transfer" as long as it does not exceed fifteen minutes. Passengers are not allowed to top up the travel card at any side to enjoy the same discount. A similar situation exists at Newton MRT station and Bukit Panjang MRT/LRT station.

Tampines station is one of the four MRT stations in Singapore that have both an above-ground platform (East West line) and an underground platform (Downtown line). The other three stations are Paya Lebar MRT station, Buona Vista MRT station and Expo MRT station.

Vehicle extrication

Vehicle extrication is the process of removing a vehicle from around a person who has been involved in a motor vehicle collision, when conventional means of exit are impossible or inadvisable. A delicate approach is needed to minimize injury to the victim during the extrication. This operation is usually accomplished by using chocks and bracing for stabilization and hydraulic tools, including the Jaws of Life. Standards and regulations for organizations can be found in NFPA 1670 and for individual members in 1006.


A wedge is a triangular shaped tool, and is a portable inclined plane, and one of the six classical simple machines. It can be used to separate two objects or portions of an object, lift up an object, or hold an object in place. It functions by converting a force applied to its blunt end into forces perpendicular (normal) to its inclined surfaces. The mechanical advantage of a wedge is given by the ratio of the length of its slope to its width. Although a short wedge with a wide angle may do a job faster, it requires more force than a long wedge with a narrow angle.


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