alt Hacker NewsThat's a bad argument. There are gasoline trucks with a GVWR of ~20,000 pounds and diesel cars that weigh less than a Honda Accord. If you actually wanted to do that then you'd instead do something like tax based on axle weight and miles traveled, e.g. by reading the odometer during inspections.
The better argument is that diesel is worse for air quality and then it's a pigouvian tax in proportion to how much you burn.
The realpolitik argument is that fewer people have diesel vehicles and democracy is two wolves and a sheep voting on what's for dinner. But taxing commercial trucks is also a pretty sneaky way of taxing ~everything while pretending to not, so it's also the principal/agent problem. Legislators want to spend money while pretending not to take it from you.
> diesel cars that weigh less than a Honda Accord.
It is taxed less than gas in lots of Europe where that is more common. You also need to factor in mpg vs gas, where it is higher, so more road-wear pCO2 was part of the debate in Europe, even though it is longer carbon chain so worse co2 ratio per calorie, the engines are more efficient. Diesel is worse for local air, better for long term co2.
There are a mixture of factors and lobbying behind the differencs, road wear is one. Farm fuel with no road wear isn't taxed much at all in lots of places and is more often diesel.