When Will is seen driving to Stanford during the closing credits, the sign on a bridge over the highway says "Prospect St., Stockbridge", which points to him being on Rt. 90 west (MassPike). This means Will was taking an 18-mile/1-hour detour through upstate NY and Cleveland, Ohio, as the faster way to go (according to Google Maps) is via Rt. 84 south through Connecticut.
However, prior to Google Maps (and indeed even today), most people driving from Boston to San Francisco take the direct route of I-90 to Chicago and then I-80 from there. In spite of Google Maps, due to higher speed limits, Will's route is actually the faster route.