Trucks and inland waterway shipping are subject to height restrictions in virtually all regions. The restriction will usually refer to the highest point on the truck or ship, whether this be a part of the vehicle’s inherent structure, part of its load or part of a temporary structure on the vehicle.
How?
There are usually signposts and often signs on maps, charts and on-line that warn of height restrictions.
Signs on Overhead Structures
On roadways, most overhead structures will display the available clearance.
For waterways, the required clearance for a bridge varies according to the water depth. Because of this, it is common to have a variable headroom warning sign in the water, anchored to the bed where the indicated clearance is varied by the water depth.
Such signage is only mandatory where the risk posed by the overhead structure warrants it.
Why?
The most common reason for height restrictions is to deal with canopies that may be too low to accommodate tall vehicles.
Another reason specifically in regard to trucking, is that a height restriction can be used as a way of limiting roads or designated areas to domestic cars and vans only. For instance, refuse amenities may not allow commercial organisations to dump their trash there. As a way of enforcing this, a vehicle height restriction may be introduced.
Consequences of Non Compliance
If a vehicle hits a low bridge, for example, the consequences could be catastrophic. In 1989 in Maryland a truck carrying an excavator that was incorrectly loaded struck a pedestrian bridge that spanned a highway. The bridge collapsed onto the evening rush hour traffic, killing one motorist and seriously injuring three others.
Detection
Some authorities have introduced automatic high load sensors. When the sensor detects a load above a given height, it may trigger a stop light or sign further down the carriageway (or waterway) and local authorities may also be automatically paged.