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A bilevel car or double-decker coach is a type of rail car that has two levels of passenger accommodation, as opposed to one, increasing passenger capacity.
The use of double-decker carriages, where feasible, can resolve capacity problems on a railway, avoiding other options which have an associated infrastructure cost such as longer trains , more trains per hour or adding extra tracks besides the existing line.
Double deck trains are claimed to be more energy efficient, and may have a lower operating cost per passenger. A double deck car may carry up to about twice as many as a normal car, if structure and loading gauges permit, without requiring double the weight to pull or material to build. However, a double deck train may take longer to exchange passengers at each station, since more people will enter and exit from each car. The increased dwell time makes them most popular on long-distance routes which make fewer stops.
Double deck cars may not be usable in countries or on older railway systems with low loading gauge, most notably the majority of the British rail network. In some countries such as the UK new lines are built to a higher than the existing structure gauge to allow the use of double-deck trains in future.