the amount of space between the top of a vehicle and an object it drives under (机动车车顶与其上方桥梁等之间的)净空 The sign on the bridge said ‘Maximum Headroom 2.5 metres’. 桥上的牌子写着“最大净空2.5米”。
the amount of space between the top of your head and the roof of a vehicle (机动车内的)头上空间