Portable speed trailers visually display drivers’ real-time speeds compared to the speed limit. These devices may be effective in reducing speeds and increasing awareness of local speed limits (Federal Highway Administration [FHWA], 2004c). Portable speed trailers are most effective when the trailer flashes “SLOW DOWN” or flashes a bright white light that mimics a photo speed camera or a blue and red light that mimics a police car when drivers are moving too fast. Some speed trailers have the capability to collect traffic count data and speed data throughout the day, which can be used to identify the most dangerous traffic times when more enforcement is needed.
In some cases, back-up speed enforcement by officers may be needed when radar speed trailers are used. If a driver fails to slow when the sign tells them that they are violating the law, an officer may stop the driver. The officer may choose to use the time to educate the driver with a warning, but a flagrant speeder needs to receive a ticket to reinforce the safety message. Typically, officers do not issue tickets based on the speed on the display unit. Instead, they use certified radar equipment if they are monitoring speed at the location.
Speed trailers are best used in residential areas and can be used in conjunction with neighborhood speed watch programs or other safety education programs (FHWA, 2002). Speed trailers need to be placed in locations where they do not block pedestrians, bicyclists, motor vehicle traffic or other vital traffic control signs. Speed trailers are not substitutes for permanent actions, such as traffic-calming treatments to address neighborhood speeding issues (FHWA, 2002).