(Corrected after a bonehead math error) I’ve had water cooler talk about the reliability of our bridges in New York State, and whether or not they can continue to withstand the weight of the traffic that goes over them. To put one’s mind at ease, here’s a back-of-the-napkin calculation of exactly what, as a lay person, to look for when deciding whether or not to cross a bridge.
An average vehicle weighs about 3500 pounds. In “bumper to bumper” traffic, a car takes up about 20 feet of lane space. A lane is about 10 feet wide, and the asphalt on that lane is about 3 inches (0.25 feet) deep.
So, one “vehicle-lane” has about 20 by 10 by 0.25 cubic feet of asphalt. That’s 50 cubic feet, or about 2 cubic yards. A cubic yard of asphalt weighs 3700 pounds, so one “vehicle-lane” of asphalt weighs about 7,500 pounds.
The car only weighs half as much as the asphalt under it.
If you’re still following this, then all you need to do is to look at the bridge surface. If the asphalt has not been stripped off, then the bridge is most likely far from collapse, since the very first thing the DOT will do is take off the asphalt to alleviate the weight. They did exactly this on Route 20 and Central Avenue in Depew around 10 or 15 years ago on the bridge in that vicinity.
It brings me peace of mind to think that all of the bridges that I drive over have asphalt on them.