Weight limits are required to ensure that vehicles exceeding a specified weight do not use a road. They are generally introduced when the road contains a structure, such as a bridge, that would fail or be physically damaged by vehicles that are in excess of the specified weight. They are supported by traffic regulation orders and are enforced by the Police. There is often an alternative route signed for heavy vehicles that are prohibited from using the route.
Weight limits should not be confused with heavy goods vehicle prohibitions that restrict the size of vehicles permitted to use the road, except for access purposes. These are generally introduced for environmental reasons.
The document in Related Downloads is regarding weight restriction in Leigh-on-Sea.