18 new coaches are being introduced on the intercity X5 service from Oxford to Cambridge.
The new fleet take to the road by the end of the year, on a service that also calls at Milton Keynes and Bedford.
The £6.5million investment will also include a new fleet of vehicles on the Cambridgeshire Guided Busway.
Andy Campbell, managing director of Stagecoach East, said: “This is great news for our customers. The X5 service is used by around 1.3 million passengers a year and provides a vital public transport link between Oxford and Cambridge.
“We are delighted to be launching these new vehicles later in the year.”