A lidar system can be provided for measuring a clearance of overhead infrastructure, such as a bridge or overpass. The lidar system can alert a vehicle driver or automatically brake the vehicle if the available clearance is smaller than a height of the vehicle. The lidar system can emit rays of light over a range of angles towards a target region where the rays of light can have a vertical span. The lidar system can then receive rays of light reflected or scattered from the target region and can determine a distance traveled by the rays of light by determining a round trip travel time of the rays. A clearance of the overhead infrastructure can then be determined using geometric relationships.