The Heathrow Airside Road Tunnel (ART) is a tunnel at London Heathrow Airport. It connects the airside roads around Terminals 1, 2 and 3 to those around Terminal 5. The tunnel was opened to traffic in March 2005 and is used only by vehicles with security clearance to drive airside. Each bore contains an unusual road layout, consisting of a single carriageway 6 metres (20 ft) wide; just wide enough to allow an airport bus (Cobus 2700) to drive past another bus stopped at the side of the road. The two tunnels are linked by escape cross-passages at intervals of 100 to 130 metres (330–430 ft).