vary from context to context

IMO:

State Transit is introducing additional services as part of the Transport for NSW Growth Bus Program.

The additional services will cater for peak hour commuters travelling to and from the City as well as families, students and pensioners moving around Sydney at other times of the day and at weekends.

http://www.sydneybuses.info/news/extra-services-for-routes-3...

Bus passengers in east London to benefit from extra services on route 5

https://www.tfl.gov.uk/info-for/media/press-releases/2014/ma...

Many secondary school students in Cincinnati travel to school on Metro buses. Metro service is provided on regularly scheduled XTRA service routes, which only operate on school days and are designed to prevent overcrowding on regular Metro routes.

http://www.go-metro.com/riding-metro/xtra-service

York residents and commuters travelling in the early morning and evening will see improvements to several key bus services from today.

City of York Council, in partnership with York’s bus operators, is supporting extra services on routes 1, 5, 6, and 44 to benefit those travelling at the beginning and end of the working day.

The following routes have been improved:

Service 1

Two extra journeys between 18:00 and 19:00 from Wigginton into the city centre.
In the evening, one extra journey from the city centre to Wigginton and one extra journey from the city centre to Chapelfields.

http://www.itravelyork.info/news/extra-buses