Roland Perry wrote:
at 21:08:37 on Fri, 20 Jan 2012, Adam H. Kerman remarked:

Off-hand I can only think of three toll routes in the UK, plus the
London Congestion Zone (which I think doesn't have a transponder).

I realise toll routes are much more common in the USA.

I didn't realize there were no transponders. It's enforced entirely
with photographs of license plates?

Even toll roads in the USA are enforced by photographs of licence plates

No one enforces toll collection with photographs of license plates as
the primary system of enforcement. It supplements transponders.

(I don't think cars without transponders are impaled on spikes).

Hah! I like spikes to protect grade crossings.

There's also some enforcement by foot patrols, although I've never been
sure how widespread they are. That's because you have to pay by the day
once inside, which can't be enforced solely by entry cameras on the
periphery.

Thanks.