Compared to normal trains:

Since platform lengths in stations are limited (300 m in regional and 400 m in main-line stations), double-decked stock is a means to increase the capacity of a line without increasing train frequency or investing into the construction of longer platforms.

Compared to wide-body trains:

• Better compatibility with infrastructure

Passenger comfort

Seating comfort on the seats adjacent to the walls is slightly reduced due to restricted space for legs on the lower deck. This is not problematic in regional or suburban transport where average trips are short. In high-speed trains comfort issues are more relevant and could be an obstacle for double-decked stock. However, existing double-decked high-speed trains in France, Japan and elsewhere are widely accepted by passengers.

Ambulant catering

The staircases pose a problem for a mobile bistro service and for the mobility of passengers in general. In the Swiss IC 2000, a stair-free upper deck has been realized for these reasons.

Boarding times

Due to the stairs the boarding times at stations are increased with double-decked stock. This should be taken into account by operators in the timetable design. For the same reason, mixed operation of double-decked and single-decked stock should be avoided as far as possible.

Technological

• Pressure-tightness: Double-decked high-speed trains must show a high degree of pressure-tightness. Especially when entering tunnels, pressure waves must not enter the passenger coaches to avoid danger of burst ear-drums. Pressure-tight high-speed stock is still a challenge for manufacturers. Therefore, DB double-deckers may not exceed 160 km/h. TGVs are not confronted with this problem since there are no tunnels in the TGV infrastructure.
• Tilting is not possible for current double-decked stock

Infrastructure

One of the main obstacles for the introduction of double-decked stock is its incompatibility with parts of the infrastructure, especially tunnels. However, in many regional networks or in flat topography, double-decked stock can be used without any limitations.

Double-decked solutions exist for all types of passenger trains. Main limitations to its applicability are:

• incompatibility with infrastructure (tunnels etc.)
• lines requiring tilting cannot be operated with double-deckers

• TGV Duplex
• Shinkansen E1.
• IC 2000