Pennsylvania Station in New York, 30th Street Station in Philadelphia, Pennsylvania Station in Baltimore, and Union Station in Washington. The main services of the Northeast Corridor are indicated using the following abbreviations. Other services are listed in the right-most column. Note that not all trains necessarily stop at all indicated stations. Amtrak corridor: A (Acela), KS (Keystone Service), NR (Northeast Regional), PA (), VT () Amtrak long distance: CD (), CL (), CS (), PL (), SM (Silver Meteor), SS () MBTA Commuter Rail: P/S (Providence/Stoughton Line), NE (Needham Line), FR (Franklin Line) CTrail: SLE (Shore Line East) Metro-North Railroad: NHV (New Haven Line) NJ Transit Rail: NEC (Northeast Corridor Line), NJC (North Jersey Coast Line), RV (Raritan Valley Line) SEPTA Regional Rail: CHW (Chestnut Hill West Line), NWK (Wilmington/Newark Line), TRE (Trenton Line) MARC Train: PEN (Penn Line) Grade crossings The entire Northeast Corridor has 11 grade crossings, all in southeastern New London County, Connecticut. The remaining grade crossings are along a part of the line that hugs the shore of Long Island Sound. Without these crossings many waterfront communities and businesses would be inaccessible from land. Except for five grade crossings, 3 near New London Union Station, and two in Stonington, all have four-quadrant gates with induction loop sensors, which allow vehicles stopped on the tracks to be detected in time for an oncoming train to stop. FRA rules limit track speeds on the corridor to over conventional crossings and over crossings with four-quadrant gates and vehicle detection tied into the signal system. History The New York to New Haven line has long been completely grade-separated, and the last grade crossings between Washington and New York were eliminated in the 1980s. In 1994, during planning for electrification and high-speed Acela Express service between New Haven and Boston, a law was passed requiring USDOT to plan for the elimination of all remaining crossings (unless impractical or unnecessary) by 1997. Some lightly used crossings were simply closed, while most were converted into bridges or underpasses. Only thirteen remained by 1999, of which lightly used crossings in Old Lyme, Connecticut and Exeter, Rhode Island were soon closed. Despite six nonfatal accidents in the previous sixteen years, there was substantial local opposition to closing the remaining 11 crossings. Outright closing the crossing would eliminate the sole access points to several of the places they served, while grade separation would be expensive and