A tight squeeze ended with an MBTA bus stuck under a bridge in Westwood on Saturday. The top of the bus was damaged and that caused natural gas to start leaking out, forcing emergency crews to evacuate a nearby store. Tanks packed with gas were strapped to the roof of the bus as it headed down East Street. The tanks smashed into a railroad bridge, temporarily stopping train service and forcing neighbors to clear out quickly. "The hissing on the video is the natural gas pouring out of the tanks," said Bobby McGee, a witness.