As I pointed out earlier this week, everyone that shops in Fort Collins pays to maintain our local roads (though it’s possible that bicyclists and transit users might pay a little more into the pot than motorists). But the flip side of that same coin leads one to ask: “Which road users make the greatest demands on those tax dollars?” Roads need to be maintained. But some vehicles cause more wear and tear than others, requiring additional maintenance.

There’s a measurement system used by street engineers called the “Equivalent Single Axle Load.” By estimating the types of vehicles that will be on the road, and their frequency of use, engineers can get a sense of how long the road surface will maintain integrity given a certain type of road surface (asphalt, cement, etc.). Heavy use areas may require more expensive, but longer lasting, surface materials, while light use areas will do fine with cheaper materials.

Speed also plays into the equation. In general, a vehicle traveling twice as fast will do twice as much damage to the road. If you think about driving behind someone on a gravel road, you’re more likely to have rocks kicked up into your windshield if they’re traveling quickly than if they’re moseying along at a gentle pace. That’s because they’re exerting more force with the wheels of their vehicle when they’re moving faster.

This example on W. Vine shows that the county saves money when repaving streets by only focusing on the part of the road damaged by heavy vehicles.

So how do various vehicles compare when it comes to chewing up the roads (and thereby costing us taxpayers more money every year)? Far and away the worst offenders are big rig trucks. The amount of damage they cause has led some to refer to the problem as the Hidden Trucking Industry Subsidy. Then there’s a range of cars that extends from the top end of the weight scale, such as the Hummer H2, down to the bottom end, such as a Smart Car. If we use the Generalized Fourth Power Law, which is a rule-of-thumb way to determine the level of damage caused by a particular load, then we can get some sense of how all of the different vehicles on the road compare in terms of how much damage they do to the surface of the street.

The American Association of State Highway and Transportation Officials (AASHTO) sets a 18,000 pound big-rig as the median vehicle size, and therefore it’s the scale against which all other vehicles are judged. (The largest vehicle allowed on the road has a maximum weight allowance of 80,000 lbs!) I picked a few random vehicles that we might see on our local roads and I’ve used the Fourth Power Law to determine how they stack up in terms of damage caused to roads.

Vehicle Approximate vehicle weight in pounds Comparative level of damage
9 ton big-rig 18,000 1.000
Hummer H2 8,600 0.0521
Chevy Tahoe 5,500 0.0087
Toyota Highlander 4,250 0.0031
Average Car 4,000 0.0024
RAV 4 3,550 0.0015
Prius 3,050 0.0008
Smart Car 1,800 0.0001
Fat Man on a Freakishly Heavy Bicycle 350 0.0000001

Even a Hummer doesn’t come close to the level of damage that a big rig truck does to our streets and highways. But for the most part, big rigs don’t regularly travel through Fort Collins (except on state highways 287 and 14). So it makes more sense to look at an average car as the base level of damage caused to the roads. (According to the New York Times back in 2004, cars weigh 4,000 pounds on average.)

Vehicle Approximate vehicle weight in pounds Comparative level of damage
9 ton big-rig 18,000 410.0625
Hummer H2 8,600 21.3675
Chevy Tahoe 5,500 3.5745
Toyota Highlander 4,250 1.2744
Average Car 4,000 1.000
RAV 4 3,550 0.6204
Prius 3,050 0.3380
Smart Car 1,800 0.0410
Fat Man on a Freakishly Heavy Bicycle 350 0.00006

It would take 410 average sized cars traveling on a road to equal the level of damage caused by one 18,000 pound big rig truck. But it only takes 21 average cars to cause the level of damage created by a single hummer.

Now let’s redo the chart from the perspective of a bicyclist. And rather than using a slim cyclist on a carbon fiber bike, let’s use the example of a large man on an old steel frame. This will give us a more conservative comparison of the levels of damage between bicyclists and other vehicle users.

Vehicle Approximate vehicle weight in pounds Comparative level of damage
9 ton big-rig 18,000 6,995,485
Hummer H2 8,600 364,520
Chevy Tahoe 5,500 60,979
Toyota Highlander 4,250 21,741
Average Car 4,000 17,059
RAV 4 3,550 10,583
Prius 3,050 5,767
Smart Car 1,800 700
Fat Man on a Freakishly Heavy Bicycle 350 1

It would take 700 trips by bicycle to equal the damage caused by one Smart Car. It would take 17,059 trips by bike to equal the damage caused by an average car. And it would take 364,520 bike trips to equal the damage caused by just one Hummer H2. !!!!!

So let’s talk about this in terms of taxes. For the sake of argument, let’s say that every 1,000 miles traveled in an average sized car equals $1’s worth of damage to the road that will have to come out of City coffers for repair work. A bicyclist would have to travel over 17 million miles to cause the same $1’s worth of damage.  Or another way to look at that, for the $1’s worth of damage that a car does to a road, a bicycle, traveling the same distance on the same road, would perpetrate $0.0005862 worth of damage. That’s about a tenth of a ha’penny.

In other words, every time you leave your car at home and take your bicycle out instead, you’re saving the City, and yourself, a car-load of money. It’s no wonder all new City streets are required to include space for bikes to share the road. The more people the City can get out of their cars and onto a bike, the more money can be spent by the City on other projects, like building a new community center on the southeast end of town.

So the next time you see a cyclist out on the street, be sure to give them a wave and thank them for all the money they’re saving taxpayers.

Spicy Garage from Ontario turned my chart into a graph and sent it in. This really helps visualize the difference between the vehicles.