The route serves to connect the Clarington communities of Newcastle, Bowmanville and Courtice as well as downtown Oshawa to trains on the Lakeshore East line at Oshawa GO Station in Oshawa for further travel westward towards Toronto.
Additionally, the route serves as a train-bus service of the entire Lakeshore East line during early morning and late night hours when the entire train line is out of service.
The train meet service operates primarily on Highway 2, while the train-bus service operates on Highway 401, the Don Valley Parkway and the Gardiner Expressway.
The 90 Newcastle-Oshawa route is a train-bus service, replacing Lakeshore East line train service early in the morning and late at night. At all other times, the route connects the Clarington community of Newcastle at Highway 2 and Beaver Street to Oshawa GO Station, making stops at the Newcastle Carpool Lot, the Bowmanville Park and Ride, the Clarington community of Courtice at Highway 2 and Courtice Road and downtown Oshawa at Bond Street (westbound) or King Street (eastbound) and Centre Street.