Acela crossing. The nation's fastest train, Amtrak's Acela Express trainset, is seen here crossing the Broadway Avenue Extension in Mystic, at the west end of the Mystic station platform. The Broadway Ave. Ext. crossing is one of eleven at-grade railroad crossings remaining on the Northeast Corridor in Connecticut. Top speed through here is 70 MPH and due to the four quadrant gates, trains do not sound their horn at this crossing.