RER A
The double-decker trains grew out of an effort to increase capacity on the RER A line, one of the world's busiest routes. These trains could carry up to 2,600 people per train, compared to 1,887 people on the single-deck trains that had been used on the RER A since it opened. These double-deck trains proved so successful and popular, operators of the RER A went on to purchase 140 MI 09 trainsets, an improved version of the MI 2N that would be built by the same Alstom-Bombardier consortium.