I think this meaning is being implied:Service is an uncountable noun in this context (and most other contexts). It should not have an article.
3a. [countable/uncountable] work, help, or advice provided by a business or organization for the public provide a service:
We aim to provide a first-class service.
I don't think the "a" is in error here, since it may refer to a dependable company that operates local buses.The town is a long way from the nearest big city. However, there is a good bus service.