Although all semi-trucks have rear guards for preventing underride accidents, trailer side guards are generally absent. Without side guards in place, an impacting car in a side collision with the trailer can resultĀ in a catastrophic underride truck accident. This hazard is further exacerbated by these dangerous habits of some inexperienced and negligent truck drivers: Poor Maintenance Semi-trucks must have lights and reflectors on the sides of their trailers for increased night visibility. Failure to replace burnt out lights and missing reflectors increases the risk of nighttime underride accidents. Equally dangerous.