Do trailers need mounted turn signal lights?

In most jurisdictions, trailers must have functional turn signal lights if their size or construction makes hand-and-arm signals by the driver inadequate or inconsistent with safe operation or if the trailer obscures the driver's hand-and-arm signals. Generally, trailers longer than 80 inches (2,032 mm) or wider than 80 inches (2,032 mm) must have turn signals. For smaller trailers, the use of turn signals is recommended but may not be legally required.