Weight limits are classed as either environmental weight limits or structural weight limits.

Environmental weight limits are normally used to prohibit commercial goods vehicles from using a particular road as a through route. They are typically provided where a route is being used as a ‘short-cut’ and where it is undesirable for goods vehicles to use the route.

Structural weight limits, as the name implies, are implemented in locations where it is not safe for vehicles above a certain gross weight. A weak bridge is a typical example of where such a restriction would be used.