For drivers, the best way of avoiding a contravention is probably to take a ticket at an entry barrier and pay on exit. But barriers are expensive to install and, because they limit the number and type of contraventions, they are far less protable for the companies. This means open sites with signs are the commonest kind of private car park. These entice motorists on to the land, oen with oers of a free-parking period. Vehicle keepers (usually the drivers/owners) who disobey the rules get a PCN for £70-100. Several of the biggest private rms rely heavily on camera surveillance, recording vehicle registration plates on entry and exit and sending PCNs by post. One company bought 807,201 datasets in 2013/14 (DVLA: FOIR 3910). At an average of £85 a time, it is chasing £6.86 million, so this is big business.