3 ms·

Road wear scales with the fourth power of weight over an axle. Most fuel consumption is about overcoming drag rather than accelerating so you should expect it t

Road wear scales with the fourth power of weight over an axle. 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. I don’t think fuel taxes are particularly good as indirect taxes on the externalities one might care about – road wear, vehicle deaths/life-changing injuries, noise, pollution, parking space in streets, passing room on narrow roads, etc.

kergonath 3y ago
> 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.
Dracophoenix 3y ago
Ultimately, the people who pay any tax are the end-consumers. A tax like the one you're proposing impacts trucks, ambulances, and buses as well as commercial ride-sharing and taxis. The final cost of the tax will be reflected in the raised prices of groceries, EMS requests, and trips to the airport.
- dan-robertson 3y ago
  I’m not proposing a tax, to be clear. One problem with these sorts of taxes on driving is that drivers often see them as a ‘service charge’ they pay to use the roads and they then expect governments to plot that money into road maintenance/construction. I think it’s not great to have a tax whose revenue that people feel should be earmarked for certain things. Perhaps something like an emissions/inefficiency levy on car tax (and based on miles driven) would help but I doubt it would be politically tenable, especially with the current government trying to de-boris their policies (and so walk back on various green things). I think part of the solution would be changing safety standards to better capture the dangers to other road users, changing liability rules/penalties to make such cars more expensive to insure (though probably the effect is too small to make much difference), having some fines scale with the value of the car (on the one hand I think people speeding, etc, in flashy cars should be particularly penalised. On the other, the UK already has some fines that are meant to scale with income and letting people off by driving smaller cars seems bad. Perhaps an alternative would be fines for certain infractions that are higher for cars that would do more damage were something to happen as a result of the driving), installing more bell bollards on corners so the people who aren’t good at staying on the road risk big dents instead of running over a toddler, and more enforcement against minor violations. Lots of those don’t specifically target oversized cars though.

kergonath 3y ago

> 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.

Dracophoenix 3y ago

Ultimately, the people who pay any tax are the end-consumers. A tax like the one you're proposing impacts trucks, ambulances, and buses as well as commercial ride-sharing and taxis. The final cost of the tax will be reflected in the raised prices of groceries, EMS requests, and trips to the airport.

dan-robertson 3y ago
I’m not proposing a tax, to be clear. One problem with these sorts of taxes on driving is that drivers often see them as a ‘service charge’ they pay to use the roads and they then expect governments to plot that money into road maintenance/construction. I think it’s not great to have a tax whose revenue that people feel should be earmarked for certain things. Perhaps something like an emissions/inefficiency levy on car tax (and based on miles driven) would help but I doubt it would be politically tenable, especially with the current government trying to de-boris their policies (and so walk back on various green things). I think part of the solution would be changing safety standards to better capture the dangers to other road users, changing liability rules/penalties to make such cars more expensive to insure (though probably the effect is too small to make much difference), having some fines scale with the value of the car (on the one hand I think people speeding, etc, in flashy cars should be particularly penalised. On the other, the UK already has some fines that are meant to scale with income and letting people off by driving smaller cars seems bad. Perhaps an alternative would be fines for certain infractions that are higher for cars that would do more damage were something to happen as a result of the driving), installing more bell bollards on corners so the people who aren’t good at staying on the road risk big dents instead of running over a toddler, and more enforcement against minor violations. Lots of those don’t specifically target oversized cars though.