2 ms·

> Road wear scales with the fourth power of weight over an axle. Cars are not getting more axles, even SUVs, so this is a constant multiplicative factor. I wou

> Road wear scales with the fourth power of weight over an axle. Cars are not getting more axles, even SUVs, so this is a constant multiplicative factor. I would be happy with a tax that scales as the fourth power of the mass, no problem. That would be actually quite dissuasive very quickly. Though even a linear scaling would be an improvement over the current situation. > Most fuel consumption is about overcoming drag rather than accelerating so you should expect it to scale with something like cross-sectional area, say weight^2/3, though making cars longer adds weight without much drag and making them boxier can add drag without much weight. Right. We should ideally account for aerodynamics and drag factors, which also keep getting worse year after year. One does not preclude the other. > I don’t think fuel taxes are particularly good as indirect taxes on the externalities one might care about I entirely agree.

michpoch 3y ago
> Cars are not getting more axles, even SUVs, so this is a constant multiplicative factor. I would be happy with a tax that scales as the fourth power of the mass, no problem. That would be actually quite dissuasive very quickly. Though even a linear scaling would be an improvement over the current situation. Sounds like we should tax EVs then: https://www.energylivenews.com/2023/06/27/evs-cause-twice-the-road-damage-of-petrol-vehicles-study-reveals/ https://www.energylivenews.com/2023/06/27/evs-cause-twice-th... The road tear on SUVs will not that that much larger, because they have wider tyres, so when you calculate kg / sqm you might get smaller value than for smaller cars.
- kergonath 3y ago
  > Sounds like we should tax EVs then No argument on my part: huge EV SUVs are also very bad.
dan-robertson 3y ago
What do you mean by constant multiplicative factor’. Are you saying that cars are perfectly balanced between front and back axels (surely a reasonable thing to want for tyre wearing if nothing else). The point about the scaling is that it is not linear: if you double the weight over an axle, you get 16 times the wear but perhaps 1.5-2x the fuel consumption. For this reason I dispute that fuel duty effectively taxes the (externalities due to the) weight of cars. Though I concede that wasn’t really the point you were making.
- kergonath 3y ago
  > What do you mean by constant multiplicative factor’. Are you saying that cars are perfectly balanced between front and back axels (surely a reasonable thing to want for tyre wearing if nothing else). Right. An implicit assumption was that the weight repartition does not change much, i.e. that if 2/3 of the weight is supported by the front axle, that ratio would be similar for a hatchback and a SUV. This does not seem completely unrealistic when comparing ICEs with other ICEs or EVs with other EVs (though EVs will have a very different weight repartition compared to ICEs due to the way batteries and motors are integrated). With this in mind, the front axle bears 2/3 * m_1 for a sedan of mass m_1 and 2/3 * m_2 for a SUV of mass m_2. So the effective weight (as seen considering only one axle) is just a linear function of the actual weight. It changes the magnitude, but it does not change the scaling.

michpoch 3y ago

> Cars are not getting more axles, even SUVs, so this is a constant multiplicative factor. I would be happy with a tax that scales as the fourth power of the mass, no problem. That would be actually quite dissuasive very quickly. Though even a linear scaling would be an improvement over the current situation. Sounds like we should tax EVs then: https://www.energylivenews.com/2023/06/27/evs-cause-twice-the-road-damage-of-petrol-vehicles-study-reveals/ https://www.energylivenews.com/2023/06/27/evs-cause-twice-th... The road tear on SUVs will not that that much larger, because they have wider tyres, so when you calculate kg / sqm you might get smaller value than for smaller cars.

kergonath 3y ago
> Sounds like we should tax EVs then No argument on my part: huge EV SUVs are also very bad.

dan-robertson 3y ago

What do you mean by constant multiplicative factor’. Are you saying that cars are perfectly balanced between front and back axels (surely a reasonable thing to want for tyre wearing if nothing else). The point about the scaling is that it is not linear: if you double the weight over an axle, you get 16 times the wear but perhaps 1.5-2x the fuel consumption. For this reason I dispute that fuel duty effectively taxes the (externalities due to the) weight of cars. Though I concede that wasn’t really the point you were making.

kergonath 3y ago
> What do you mean by constant multiplicative factor’. Are you saying that cars are perfectly balanced between front and back axels (surely a reasonable thing to want for tyre wearing if nothing else). Right. An implicit assumption was that the weight repartition does not change much, i.e. that if 2/3 of the weight is supported by the front axle, that ratio would be similar for a hatchback and a SUV. This does not seem completely unrealistic when comparing ICEs with other ICEs or EVs with other EVs (though EVs will have a very different weight repartition compared to ICEs due to the way batteries and motors are integrated). With this in mind, the front axle bears 2/3 * m_1 for a sedan of mass m_1 and 2/3 * m_2 for a SUV of mass m_2. So the effective weight (as seen considering only one axle) is just a linear function of the actual weight. It changes the magnitude, but it does not change the scaling.