How do you distribute the money to places where people drive but don't live? Gas tax handles this to an extent, but milage tax wouldn't; not without border checkpoints or mass surveillance.

The government has stats on how busy easy road is. Just pool all of the money and distribute it based on those stats.

To give an example - in my hometown in a few places there are small wires on the road surface that measure the number of cars that drive over it. Private by default!

I don't think Odometers are reliable enough, especially as the basis for a tax. You'd certainly see an increase in average tyre size!

They're probably accurate to within less than 10%. How many kilometers would you have to drive to save a dollar from slightly bigger tyres?

I was being slightly facetious in referencing tyre size, although people regularly have to adjust speedo/odometers by 10% or more when fitting large tyres on off-roaders.

Odometers can have their values changed at will, at least in ICE vehicles, often for valid reasons.

Fudging do numbers illicitly is already a huge no-no in the US.

It also is in Ireland, but there are valid reasons, such as as replacing an ECU or dash cluster.

Unless auto manufacturers are required to fit much more secure odometers, I can't see them in their current incarnation used as the basis for a tax.

New Zealand collects road tax on diesel vehicles using odometer readings. It generally works for heavy commercial vehicles where the owners have more to lose risking fraud but I know private vehicle owners who would wind back or disconnect their odometer to avoid the tax.