The F-150 Lightning: A Little Heavier, A Lot More Damage

15 Jun 2021

It’s well established that humans are bad at exponential math (the wheat and chessboard problem dates back to at least the year 1256). So when I read this passage in Slate about the issues with the new electric Ford F-150, I took note (emphasis mine):

Finally, there is the question of infrastructure. The impact of even a superheavy passenger vehicle like a Hummer pales in comparison with an 18-wheeler; it’s not like our bridges are going to collapse when all the F-150s turn electric. The problem is less that heavier vehicles will wear down the roads at a slightly faster pace, but more—since their owners are freed from gas taxes—they won’t be paying for it.

To be clear, I agree with the main point of the article, that having super-heavy passenger vehicles on the road causes a lot of problems (and the F-150 is a passenger vehicle for most people most of the time–how many pristine trucks do you see driving around without anything in the bed or attached to the hitch?). However, “wear down the roads at a slightly faster pace” is misleading at best. Highway agencies in the US generally use the “fourth power rule” as a rule-of-thumb for predicting how vehicle weight affects maintenance costs. What this means is that road wear increases with the vehicle’s axle weight raised to the fourth power. So, if a vehicle is twice as heavy (and has the same number of axles), it will do 16 times as much damage to the roads.

The Slate article says that the truck weighs 35% more than its gas-powered counterparts, which doesn’t really sound like a lot, but when you raise it to the fourth power (1.35^4), you get 3.32, which means that we should expect the electric F-150 to do more than 3 times the damage to the roads than its gas-powered counterpart. I don’t think that most people would consider tripling to be a “slight increase”.

This gets us to the second part of the paragraph, where the author mentions that the trucks won’t be paying their fair share. This is true, of course, but it forgets the current reality that their gas-powered siblings don’t pay their fair share, either. The gas tax currently pays for less than half of highway and road costs, with the rest coming from general funds and bond revenue (which probably aren’t going to be paid by future gas taxes anyway, regardless of their intent), and gas tax revenue is disproportionately spent on highways (the more local the road, the more of its funding comes from the general fund). The adoption of electric vehicles will have a huge impact on highway and road funding, but it’s not like the system was doing fine until they came along, the Highway Trust Fund has been reliant on regular infusions of cash from the general fund for a while now. Switching to electric vehicles is just adding stress to an already broken system.

So What?

I imagine that you may be reading this and agreeing with me, but thinking that it’s pretty abstract. By my logic, a heavier pickup truck that probably won’t be a significant chunk of the market for a while pales in comparison to the impact of people purchasing heavier vehicles in general (there are a ton of SUVs out there and pickup trucks outsold cars for the first time ever in 2020). Our roads haven’t eroded out of existence. But we haven’t been spending money on improving them, either. For example, I just stumbled upon the Thurston County Transportation Benefit District, which is appropriately shortened to TC-TBD since it appears that in 6 years they have yet to raise any money or start any projects (in essence, what they will actually do is To Be Determined). Here’s their answer to the question “What happens if no funding is approved?” (from the FAQ).

Roads will continue to deteriorate as insufficient funding is available for pavement preservation; the County’s neighborhood traffic calming program will continue to be unfunded; and fewer roads will have fog lines, a proven, low cost means of reducing traffic accidents.

The Olympia Transportation Master Plan paints a similar picture, though they do set aside some money for active transportation projects (which will be finished in about 137 years, if none of that money needs to be diverted to road maintenance).

Is vehicle weight solely to blame for this persistent funding shortfall? Certainly not. After all, we could choose to increase funding. Unfortunately, increasing usage fees like the gas tax is generally considered to be political suicide, and here in Washington, with our regressive tax structure, finding other money is difficult. It seems reasonable, then, that the trend of increasing vehicle weight is going to continue to break our infrastructure funding system.

Won’t things get bad enough that we are compelled to fix the system?

In a word, no.

Since vehicles are getting heavier and people in the US seem to be allergic to higher usage fees (I-976 passed here in Washington, the federal gas tax hasn’t been raised since the early ’90s, the TC-TBD has been unwilling to implement a county car tab fee, etc.), usage fees are going to cover a decreasing share of road maintenance. Roads are essential, so we will find a way to pay for them, which means that money is going to come out of the general fund.

Spending money from the general fund isn’t the worst thing in the world (after all, there is a societal benefit to a road network), but if it causes the funding to be delayed, that will end up costing us a lot more money in the end. A lot of road maintenance consists of patching small cracks and holes in the pavement, if we defer this due to lack of funding those cracks and holes won’t get patched, allowing them to worsen. Not doing this small maintenance shortens the lifespan of the road, since the road surface is what is protecting the roadbed, and once the roadbed gets damaged, you can’t just resurface the road (which is already expensive) but are instead looking at road reconstruction (which is as expensive as it sounds).

In short, electric vehicles pose a two-pronged threat, in that they will cause a lot more wear on our roads and that we appear to be unwilling to update our road funding. I’m picking on the F-150 here, but the same logic can be applied to any electric vehicle from Tesla to Hummer (which will weigh something like 9,000 pounds), and will hold true until we figure out how to make an electric vehicle that doesn’t need 1,000+ pounds of batteries.

Notes

• To be clear, I’m all for electric vehicles. I think that spending more (even a lot more) on roads is a small price to pay for, you know, having a liveable planet. I do take issue with the idea of them being thought of as a complete solution, but if you’re going to have cars and trucks, they should be electric.
• For more discussion about how roads are paid for, Who Pays for Roads by U.S. PIRG is a good start.
• To be fair, the “fourth power rule” is a rule of thumb. According to a research paper on Repricing Highway Pavement Deterioration, “Depending on the definition of pavement damage (loss of serviceability, roughness, rutting or cracking) the appropriate power ranges from 3 to 6 or more.” This means that the increased wear from the vehicle could well be lower than what I listed above (1.35^3 is only 2.46), but it could also be a lot higher (1.35^6 is 6.05). Given this context, I think that the fourth power rule sounds reasonable. That being said, I would like to see newer research on the topic (the rule was based on studies done in the 1960’s).
• This is the same reason why the argument that people on bicycles don’t pay their own way. If my bike weighs 250 lbs when I’m riding it, and I pay, say $0.01 per mile (or about $25 per year), for it to be fair, the driver of a car that weighs 2500 lbs should be paying about $100 per mile (since a vehicle that is 10x heavier is causing about 10,000x the wear on the road), or about $1,400,000 per year (the average American drives about 14,000 miles per year), which is absurd. To get down to a reasonable level, say $1,400 per year (1,000 times less), a person on a bicycle who is charged at the same rate would be paying $0.00001 per mile, or about $0.025 per year for someone who rides 2,500 miles. I’m happy to pitch in a nickel towards road maintenance every other year to pay for the wear and tear I put on the local roads, but it might just be easier to deduct it out of the taxes which I already pay for roads (since less than half of highway and road spending comes from user fees–including gas tax).