Ben Laurie blathering

Privacy Preserving Road Usage Charging

I recently attended a conference on “Respecting Privacy in Global Networks“. One of the talks was about road usage charging – the general idea being that instead of paying a flat fee related to your vehicle type, you pay for the roads you actually use. Of course, the obvious ways to implement this (either using a GPS to log a trail to some kind of secure device which is periodically examined to determine fees, or by collecting car details with roadside receivers) are stupendously privacy invading.

But, it occurs to me, we have the technology at our fingertips to make this system anonymous (except for defaulters) quite easily. All we need to do is fit cars with a device that can spend anonymous digital cash as they pass checkpoints. Cars that don’t fork out get their numberplate photographed. Obviously you have to back this up with legislation that forbids checking numberplates except on defaults but that seems easy enough.

Of course in London we should have this system for congestion charging, which already monitors everyone’s movements.


  1. the other advantages of digital pay-as-you-go is that it is country-neutral (anyone can fit a receiver), and it is much harder to subvert than GPS.

    it doesnt matter how secure your GPS tracelog device is, (civilian) GPS itself can be subverted. I could snip the antenna and hook the gps receiver up to a fake signal generator whose tracelog would be ‘no movement’ or ‘driving round a country with no road fees, well below the speed limit’.

    The reason GPS doesnt get subverted today is that it isnt used for pricing or speed controls.

    Comment by Steve Loughran — 18 Apr 2007 @ 13:23

  2. I believe Chaum described attempting this back in the day. I think it was on his list of attempts for good use that he described at the “blinding patent expiration party” in Palo Alto.

    Therefore I just assumed the toll-taking vendor marketplace knew of this and was ignoring it 😉

    Comment by Rodney Thayer — 28 Apr 2007 @ 18:26

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