When a city extended its evening bus service, more residents used public transport after work. A survey also found that some passengers had previously walked, while others had previously driven. The increase in passengers therefore could not be translated directly into an equal decrease in car journeys. The environmental effect depended partly on which trips had been replaced and how full the additional buses were. This did not make the service unsuccessful. It might improve access to jobs or make late travel safer even where the reduction in driving was modest. Evaluating the service required separating several outcomes that often appear together in public discussion. More passengers, fewer car trips, lower emissions, and better access can be related, but none should be used as an automatic substitute for measuring the others.