A trailer is a wheeled device, attached to a vehicle, used for transporting goods. It may be used for shipping, hauling or moving equipment, as well as a means of transportation for children and pets. A trailer can be made from a variety of materials, such as steel or aluminum, and can be designed to carry specific types of goods. An aluminum trailer can be one of the lightest and most durable options available today. Aluminum can also resist rust better than most other metals and requires less maintenance over time.
Often, trailers are used to advertise films that have not yet been released. They can be shown in a cinema before the feature film, or they may be presented as a separate program on DVD or other video format. In the latter case, many DVDs are marketed specifically as collections of film trailers, sometimes referred to as “trailer trash.”
Trailers are often created while the underlying film is being edited in the studio. They are typically edited from rushes or dailies, so they may contain footage that is not included in the final film. The film editor may also use different takes of a shot than the trailer editors, and thus the trailer may not accurately represent the finished film.
Some trailers are composed entirely of music and special effects, with no actual video footage. This is common for horror movies, and it can work well in creating a sense of tension and mystery before the main film is seen. Some modern film trailers are mixed in Dolby Digital stereo, enhancing the impact of the scenes by increasing the spatial separation of sound elements.
When a trailer is transported over long distances, it is often accompanied by an escort truck. This escort provides assistance in the loading and unloading of cargo from the trailer, and it can help with securing the load. The escort truck can also help with the transfer of cargo to and from a railcar or ocean container at ports.
Depending on the type of trailer, it can be equipped with a variety of safety features to protect the driver and the cargo. For example, a trailer can be fitted with an anti-lock braking system to prevent the wheels from locking when braking under load.
A trailer may also be equipped with an electronic logging device to replace traditional paper logs. This can reduce paperwork and improve efficiency. Other trailer safety features include load locks to secure cargo in place and an emergency braking system.
If the trailer has a dual axle, it can be used to haul a heavier load over longer distances. It can also be used to carry a tall load that cannot fit on a flatbed trailer. A hydraulic trailer can also be used to move oversized loads, such as bridge sections, building modules or ship sections. It can also be used to haul oil rig modules. A trailer can be fitted with a special coupler to connect to a ballast tractor.