I suspect, requiring all cars to have a telematic device is the answer here. Insurance companies are already using these and the behaviour of individuals drastically improves when one is installed.

This has an advantage in enabling provision of a device at country borders etc.

Another option is to develop a cheap Automatic Number Plate Camera and create a network of cameras across our road systems.

Both approaches not only allow road pricing strategies, but also address speeding.

This may be a bit big brother for some but this is pretty much the way I see us heading.