Smalltown had a problem with people parking cars on the town's mam shopping streets instead of in the nearby car parks The parked cars created congestion and made it difficult for delivery vehicles to unload Smalltown's local government had employed traffic wardens to enforce parking regulations by issuing parking fines to motorists who parked for more than the permitted 30 minutes. The local government took further action to deal with this problem It banned parking on the busiest streets, it introduced parking charges in the remaining streets and it made it free to park m the town's car parks for up to two hours Fewer people now park cars on the streets because of the charges, but those who do generate significant revenues for the local government Fewer traffic wardens are required and so wage costs have reduced The local goverment auditors have decided to carry out a value for money audit of the parking system Which of the following is a measure of effectiveness?