Bilevel rail car

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 railroad, 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 bi-level 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.

Source: Wikipedia