The route serves to connect Uxbridge to trains on the Stouffville line at Lincolnville GO Station in Whitchurch-Stouffville for further travel southward towards Toronto during the more central peak hours, as Uxbridge is out of reach from the train line.
Additionally, the route serves to connect Uxbridge, Whitchurch-Stouffville and Markham to trains on the Stouffville line at Unionville GO Station in Markham for further travel southward towards Toronto during late morning and early afternoon peak hours, as the portion of the train line between Lincolnville GO Station and Unionville GO Station is out of service at those times.
The 70 Uxbridge-Stouffville-Unionville route is a train-bus service, providing late morning and early afternoon peak service to/from Uxbridge to connect to the Stouffville line at Unionville GO Station, making stops in the Uxbridge community of Goodwood, Lincolnville GO Station, Stouffville GO Station, Mount Joy GO Station, Markham GO Station and Centennial GO Station. During the more central peak hours, when service between the Lincolnville GO Station and Unionville GO Station is provided by the Stouffville line, the route provides service to/from Uxbridge to connect to the Stouffville line at Lincolnville GO Station, making a stop at the Uxbridge community of Goodwood.
Note that all buses serve the Centennial, Markham and Stouffville GO Stations from bus stops on the street, as opposed to bus terminals on site.
With newer train runs steadily being introduced on the Stouffville line later in the morning and earlier in the afternoon peak hours, new branches of the 71 Stouffville train-bus route were introduced specifically to connect with these trains at Unionville GO Station, due to their inability to proceed further north. On April 6, 2013, combined with newly introduced branches to meet increasing demands on the train line, route 70 was spun off from branches of the 71 Stouffville train-bus route that did not provide service to the Union Station Bus Terminal in downtown Toronto, but instead connected to the Stouffville line at either Lincolnville GO Station or Unionville GO Station These former branches include the 71K, 71J and the long-ago introduced 71B, which respectively became the 70, 70E and 70B.