In message , at 10:29:43 on Mon, 5 Nov
2012, tim..... remarked:
Especially if they continue to make it free between 22:00 and 06:00.
How will someone know if they have snuck into the free period and thus
don't have to phone up to pay, or just missed it by a couple of seconds
and do?

They could send that hat round for an illuminated sign informing road
users of the situation.
--
Roland Perry