High-voltage direct-current and alternating-current systems for interurban railways

The magnitude and direction of engineering development in apparatus for the electrical equipment of high-speed interurban railways is well illustrated by a study of the systems adopted by some of the more important lines recently built or now under construction. These systems may be divided into three classes, namely: 1. 600-volt, direct-current using either overhead trolley or third-rail. 2. 1200-volt, direct-current overhead trolley. 3. Single-phase, alternating current, 3300- or 6600-volt overhead trolley.