Heavy traction problems in electrical engineering

Broadly speaking, all traction on rails can be subdivided into the following three classes: 1. Street railways, devoted almost exclusively to passenger traffic, operating over restricted areas, with single cars, at comparatively regular and short intervals and with frequent stops, the maximum speed being limited by the use of the public highways. 2. Rapid transit systems, comprising elevated railways, subways, suburban, and interurban lines, operating over their own right of way a traffic otherwise similar to that handled by street railways, the main difference being the use of somewhat larger units, higher speeds, and greater distances between stops. 3. Through lines, characterized by a combination of passenger and freight traffic, handled over great distances, in large units, at longer and not necessarily regular intervals, and with stops few and far between. This latter condition, however, is one of degree, and this class is meant to include through trains of the local as well as the express kind, but not suburban trains, which properly belong to the second class.