They were use for the 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 (which require longer station platforms), more trains per hour (which the signalling or safety requirements may not allow) or adding extra tracks besides the existing line.
A bilevel car may carry about twice as many as a normal car, without requiring double the weight to pull or material to build. However, a bilevel train may take longer to exchange passengers at each station, since more people will enter and exit from each car.
The Bilevel cars may not be usable in countries or older railway systems with low loading gauges This includes much of the rail network in the northeast of the USA and almost the entire 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.
The Bilevel trains are claimed to be more energy efficient, and may have a lower operating cost per passenger.
These cars are seen in lots of countries, And states from all over the world like Argentina, Australia, Canada, China, Denmark, Finland, France, Hong Kong, India, Israel, Italy, Japan, Russia, Slovakia, Sweden, Switzerland, Ukraine, United Kingdom, And the United States.
These cars are for Long-distance trains like the Northeastern United States and Quebec like California, Florida, Illinois, New Mexico, And lots of Other countries.