Based on extensive research by the American Association of State Highway Officials, it is universally accepted that the amount of road damage caused by overloaded truck varies with the 4th power of the overload ratio. Based on this well-known Fourth Power Law, a 30 ton overloaded truck contributes damage to the road and consumes a portion of its service life as much as 4.6 times of a standard 21 ton truck. If we consider an inbound truck lane of the main highway that is predominantly used by 30-ton overloaded trucks, the service life of this traffic lane will be reduced from the intended 15 years to 3.16 years. In 1997 just before the crisis, truck transport is estimated to number around 214,000 trips per day carrying a payload of 1.2 million ton. Ordered by weight, the shipments are construction materials, agricultural products, consumer products, minerals and petroleum products.
Truck transportation is so predominant that other modes of transportation are almost non-existent.
It is estimated that the excess capacity of railway transport remains at 1.4 million ton per year. Road Safety Road safety is a major concern with heavy trucks. Despite the claim that trucks are today built with better steering power and braking system, heavy trucks running at a high speed are prone to serious accidents and become hazardous to other road users. The second issue is whether Thailand should officially raise the highway standard, say, from a standard axle load of 8.2 ton to 12.1 ton. There is a cost involved.