Automated Toll Systems: Payment through Transponders and Handling Faulty Transponders

[zak100]

Hi,
I have a confusion about transponders in automated Toll Systems. I know that they are useful to avoid huge traffic gathering at the Toll booths. But then we have transponder only lanes. Transponders are detected by sensors. But how these fast vehicles fitted by transponders are charged with Toll fees. I mean once the car is detected in the transponder lane what are the remaining functions till the car leaves through the transponer only exit lane and how they performed?

There are no barriers, so if there is a problem with the transponder, how this problem is detected if the car leaves through the transponder only exit lane.

Some body please guide me.

Zulfi.