The Westport Fire Department responded to a brush fire on interstate 95 northbound between exits 18 and 19 this afternoon.  First arriving fire companies found a large area of brush burning and quickly spreading.  Firefighters immediately began extinguishing the fire, but it quickly spread and crossed over the train tracks.  This necessitated a stoppage of all Metro North and Amtrack trains traveling through the area.  Firefighters from Wilton and Weston responded to the scene with water tankers to provide water supply for the operation from the highway side of the incident.  Utilizing access off Gray Lane, Fairfield Firefighters assisted Westport Firefighters extinguish the fire on the opposite side of the tracks.  The fire was extinguished and contained to approximately 1.5 acres.  The cause of the fire is unknown currently.