The Interstate 35W Bridge that collapsed in Minnesota was built in 1967. Since then there has been significant increases in the size, weight and numbers of trucks on our interstate highway system. There is no question that the additional numbers, and the increasing weight, of tractor trailers on our highways causes additional wear and tear on our roads and bridges. What impact did this have on the Minnesota bridge collapse?

The last change to national policy on truck size and weights was promulgated through the 1982 Surface Transportation Assistance Act (STAA). Since the 1982 STAA, 14 states adopted some type of incremental expansion (state-by-state) which promoted the use of longer combinations vehicles (LCV) though special access highway systems before it was halted by the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA). 

Truck size and weight regulation standards can be divided into three types: prescriptive standards, like those currently applied in the U.S.; parametric standards, which include parameters known to be related to performance; and pure performance-based standards. Most size and weight regulation in the U.S. are not based on pure performance tests or on performance-related parameters. They are based on historical compromises between trucking and shipping interests and state and federal highway agencies. These are prescriptive standards, and they are relatively simple to enforce.

Assuming one pass of the 8-tonne axle is equal to 10 passes of light vehicles, as
used in current chipseal design and performance modelling, then one pass of a 12-
tonne axle is equal to 23 passes.

The American Society of Civil Engineers stated it this way in a 2006 report:

Trends continue toward larger trucks and smaller passenger vehicles along with increasing truck volumes. Operational and safety issues and highway pavement and geometric design aspects, of mixing large trucks and smaller passenger vehicles will continue to be a subject of importance to highway administrators and designers…

Increases in truck sizes and weights impact negatively on the structural life and geometric adequacy of the present road network. All highway users will experience reduced service levels, delays, increased vehicle wear and operation costs, and reduced safety. These negative impacts must be balanced against productivity gains and reduced commodity costs.


Given the above, what is the remedy? Is it enough that we have cheap goods, whatever the cost in lives? I believe Congress will be debating these issues shortly. What should we tell our representatives? Your thoughts greatly appreciated.