If you want to quickly grasp the current proposal in Washington to increase the weight limits on shipping trucks, your first stop should be the zoo.

There, you could set your sights on the giant of the savanna, an adult elephant — all 5½ tons of him. Now imagine the weight of that elephant being added to the load of an 18-wheeler that you’ll pass on your way home with your family.

If certain shippers get their way, this soon could be the reality on the already-strained roads and bridges in my home state of Ohio and across the United States. Special interest groups are pushing for the current highway reauthorization bill to include an increase in the federal limit on truck weight to 91,000 pounds from the current maximum, 80,000 pounds.

Who pays? Taxpayers 

The ramifications of this in all 50 states would be enormous and the numbers are certainly not on the side of those wanting heavier trucks. If a 14 percent load increase is allowed, we’ll see the rapid deterioration of our already-frayed infrastructure, damage that will ultimately force taxpayers to foot the bill at a time when they’re already subsidizing these heavy trucks.

A U.S. Department of Transportation study has shown that taxpayers already pony up 20 percent of the cost of highway damage caused by trucks weighing 80,000 pounds. Should that limit increase to 91,000 pounds, the taxpayer burden would grow to 50 percent. It’s a simple matter of engineering: If you put more weight on roads, they have to be repaired and upgraded sooner.

Another DOT study, released just this past June, found that if federal truck weights were increased to 91,000 pounds, the added stress to bridges would require either strengthening or replacing about 4,845 bridges at an estimated cost to taxpayers of more than $1.1 billion. That’s on top of the $2.4 billion for damage already done by trucks at the current weight limit of 80,000 pounds. It is important to note that this study only took into account a sample of the nation’s bridges and that the impact of this proposal is likely much larger than quantified by the study. At a time when more than 144,606 — or 24 percent — U.S. bridges are already deficient, can we really afford to make this bad problem worse?

This certainly resonates in Ohio, which has the second largest number of bridges in the country — 44,000 of them, trailing only Texas. We’ve load-rated every bridge in our state, a task that took five years. We did so in the wake of the tragic I-35 bridge collapse in Minneapolis in 2007. We’d have to start that process anew if the load limit were increased, costing Ohio $60 million overnight.

By the way, more than 5,300 of our bridges have been deemed functionally obsolete or structurally deficient and need to be replaced. The funds simply aren’t there. As to our county bridges that still have wooden decks, some of these would have to be posted or closed for the safety of the traveling public. And I surely wouldn’t want to see how long they would last against 91,000 pound vehicles.

What proponents say

Proponents of this legislative proposal will make two arguments, both weak. First they claim that the addition of a sixth axle would ameliorate the damage that the heavier weight would cause. In Ohio, nearly 3 in 4 bridges are long enough that the bridge would bear the entire weight of the truck all at once. It’s fine that the weight is spread more evenly, but that does nothing to ease the strain on a bridge.

The other argument is that the weight increase would apply to the Interstate Highway System, and not every road. If every heavy truck began and ended on an interstate, this distinction would matter. But as we like to say, all travel starts and ends on a local road. You don’t go from Cleveland to New York just on interstates.

For our safety and for the stability of our highways and bridges, let’s leave this 5½-ton elephant where he belongs: at the zoo.

Brought to you by the Association of American Railroads.