Monday, 4 June 2012

More on Vehicle Excise Duty

Sometimes I hate twitter.  It makes me do stupid things.  Like get out of bed to write a blog post on Vehicle Excise Duty at 1:30am

I've been having a discussion on Twitter with Lee Massey (@threeamp1) over VED, and how it could be made fairer.

We both seem to agree on the idea that charging for the amount of wear that your choice of transport does to the road is the best way forward.  Where we disagree is on how to measure that damage.

He suggests that the only two things that are important are the mass of the vehicle, and the distance that it travels. He also suggests that it needs to be based on the actual wear that has taken place.

I would suggest that a better proxy for the wear on the roads is the force that could be exerted on them by the vehicle, combined with the distance traveled.

All taxation schemes have to have a simplification in them somewhere, mine in this would be to use maximum potential wear, rather than absolute wear.  The use of absolute wear would require constant tracking of every one of us, for every minute that we were travelling.  This not only has huge technology cost implications, but also massive privacy ones too.

Physics tells us that force is equal to mass times acceleration.

Car manufacturers are really good at telling us a number of things about their cars.  Their weight, and their 0 to 60 mph time.

Whilst Mass is not Weight, since everything that we are measuring is under the Earth's gravity, we can just use the posted weight as a mass.

I've thrown together a quick table of transport modes, and what their VED ratios per 10,000 miles would be under my proposed system.

I've only thrown a few cars into there, and I'm quite liking the results.  There is no method of taking into account how good or bad a vehicle is in terms of fuel usage, but on the basis that a less polluting car will use less fuel, I'm inclined to suggest that taxing fuel is a better choice for this.

Part of the point of this exercise was to try and find a relative amount of VED for a bike.  I'm going to dig into this a bit more, but since most cyclists don't ever reach 62mph (100kph), it's going to be tricky.  I'll look into it more later on today, but on the basis that a bike ways 8kg, and a cyclist could get to 62mph in a minute, a cyclist does over 600 times less damage to the road than the best car that I've stuck in so far.

I'll update this post later, and increase the table with other vehicles as they are suggested to me.


  1. Note that there's a really easy way to approximate actual force applied by the vehicle. Simply measure the vehicle's fuel consumption, and adjust for weight; as an approximation beyond that, you can assume that heavier vehicles need more fuel to get to a given speed, and simply measure fuel use to determine the damage done by a vehicle, as compared to a pedestrian. As a result, fuel taxes are also the best way to make drivers pay proportional to the damage they do to the roads.

    Measuring a bike in the same manner is a bit harder - you cannot easily determine what fraction of the rider's fuel consumption is applied to the bike wheels. However, given the weight difference between a pedestrian and a cyclist, it's probably fair to assume that a cyclist does no more damage than a pedestrian, and to charge them nothing for that damage.

    If you really want to improve things, playing with VED is not the answer - most of its goals can be better met by removing VED and increasing fuel duty, keeping the tax bands as simply the way we determine the duty applied on the initial sale of the car.

  2. hmmm, you neglect the non linear relation between applied force and damage resulting. Below a certain level essentially no damage will be occuring above this level lots of damage will occur. You need to weight the distance/time spent accelerating by the momentary force applied.