The truck that broke the bridge’s back?

Could overloaded heavy-duty trucks have contributed to the damage to the Kaserne Bridge?

In South Africa, heavy-duty commercial vehicles travelling on most of the country’s national roads and
highways are subjected to strict and professional policing, to ensure that they are not overloaded and confirm to the South African Road Traffic Regulations.

Unfortunately, there is very little evidence of heavy-duty commercial vehicles being checked for overloading in the metropolitan areas of Gauteng. Could overloaded heavy-duty vehicles have contributed to the damage to the Kaserne Bridge in Johannesburg, resulting in the need for an expensive repair?

The South African Road Traffic Regulations regarding maximum axle-mass loads are clear and concise and designed to ensure that roads and bridges in South Africa are not damaged by overloaded vehicles.

There are a number of checks that have to be done to ensure that a heavy-duty vehicle complies with all the regulations pertaining to axle-mass loads and the bridge formula.

The entire vehicle, or combination, must be weighed to ensure that it does not exceed the total permissible legal mass, while each axle or axle group must be weighed to ensure that the maximum axle-mass limit as prescribed in the regulations is not exceeded.

Point loading on the surface of roads and bridges is a major cause of road and bridge damage. To protect South African roads and bridges, Regulation 241 (commonly referred to as the bridge formula) was introduced in 1992. It is designed to ensure that the axle spread of a vehicle, or combination of vehicles, is sufficient to eliminate point loading on the bridges and roads.                     

It is when consecutive axle groups of large heavy-duty vehicles are too closely positioned that point loading occurs, which causes the damage.

Regulation 241 states that “no person shall operate on a public road a vehicle, or combination of vehicles, the wheels of which are fitted with pneumatic tyres, if the total axle-mass load of any group of axles of such vehicle, or combination of vehicles, exceed the mass in kilograms determined by multiplying the dimension of such group by 2 100 and adding 18 000”.

Again, sadly, there is very little evidence of this regulation being enforced in the metropolitan areas around Gauteng.

How safe are our bridges?                           

In South Africa we have approximately 30 000 road bridges, some of which were constructed 100 years ago. Many of these are still in use today. Records illustrating the designed load-bearing capacity of these old bridges are not all available.

Added to this problem is the fact that in the past each province designed its own bridges, so no common bridge-loading capacity applies to the country’s network of bridges. It is, therefore, necessary to apply the bridge formula to all vehicles and combinations to ensure that these old bridges are safe to use.