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> Why weight in particular? Kinetic energy (thus fuel consumption and particles from brakes) and road wear scale with weight. It's not perfect but it's most of

> Why weight in particular? Kinetic energy (thus fuel consumption and particles from brakes) and road wear scale with weight. It's not perfect but it's most of the way there. > Two arguments here: 1. SUVs are already taxed on weight indirectly - they consume more fuel which is heavily taxed (50+% in most of Europe). This does not solve the issue with externalities: fuel cost absolutely does not offset the cost to society caused by car use, same for accidents and road wear. > 2. SUVs are already taxed higher because they're more expensive. They are not taxed higher, they have exactly the same VAT as any other car (give or take specific government schemes to incentivise things like hybrids and TVs). > SUVs usually have great visibility because of large windows. SUVs have terrible visibility and situation awareness because of huge blind spots and higher sitting positions for the driver (which is better on motorways, but terrible in cities). They are also much worse for pedestrians and cyclists in case of a collision.

dan-robertson 3y ago
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.
michpoch 3y ago
> They are not taxed higher, they have exactly the same VAT as any other car (give or take specific government schemes to incentivise things like hybrids and TVs). They're absolutely taxed higher. $100k SUV will cause a much higher VAT you need to pay than $50k sedan. So by buying a more expensive car you do contribute more taxes to the state funds. > SUVs have terrible visibility and situation awareness because of huge blind spots and higher sitting positions for the driver (which is better on motorways, but terrible in cities). Any sources on that? It's clearly not my experience. Most SUVs have much bigger side mirrors and the side windows are much larger (because the car is taller). Please compare cars of similar length (so not large SUV vs a hatchback). > This does not solve the issue with externalities: fuel cost absolutely does not offset the cost to society caused by car use, same for accidents and road wear. The premise is: does the tax on the additional fuel spent by driving a SUV offset the cost to the society, comparing with driving a similarly-sized but non-SUV vehicle? Making it a clear example: is driving a BMW X5 that much worse than driving a BMW 5 series (both are similar length, X5 is ~300 kg heavier)?

dan-robertson 3y ago

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.

michpoch 3y ago

> They are not taxed higher, they have exactly the same VAT as any other car (give or take specific government schemes to incentivise things like hybrids and TVs). They're absolutely taxed higher. $100k SUV will cause a much higher VAT you need to pay than $50k sedan. So by buying a more expensive car you do contribute more taxes to the state funds. > SUVs have terrible visibility and situation awareness because of huge blind spots and higher sitting positions for the driver (which is better on motorways, but terrible in cities). Any sources on that? It's clearly not my experience. Most SUVs have much bigger side mirrors and the side windows are much larger (because the car is taller). Please compare cars of similar length (so not large SUV vs a hatchback). > This does not solve the issue with externalities: fuel cost absolutely does not offset the cost to society caused by car use, same for accidents and road wear. The premise is: does the tax on the additional fuel spent by driving a SUV offset the cost to the society, comparing with driving a similarly-sized but non-SUV vehicle? Making it a clear example: is driving a BMW X5 that much worse than driving a BMW 5 series (both are similar length, X5 is ~300 kg heavier)?