Roads also cover streets, bridges, tunnels, supporting structures, junctions, crossings and interchanges. There were nine border crossings between East and West Berlin. Four significant railroad crossings were built over the lake. Ferries also helped prevent death by drowning at river crossings. There are three River Thames road crossings in the Borough. The latest tunnels are the Dartford Crossings. There are fifteen U.S. federal border crossings between Vermont and Canada. One of the few railway crossings across the canal was near Welland. There is also a risk of pedestrians walking onto the tracks at level crossings. The bombing disrupted rail traffic through London without destroying any of the crossings. There are also two international border crossings nearby for commercial and noncommercial vehicles. Some light tanks require no modifications for river crossings. Italy has 11 rail border crossings over the Alpine mountains with its neighbouring countries. Most traffic consisted of loads delivered to rail crossings. The city shares a border with Mexico that includes two border crossings.