From a brochure introducing the now-infamous A/B stopping pattern on Chicago’s “L”.

A trial run of the (mostly) alternating stopping pattern—designed to speed up operations on lines where there was no extra passing track for express services—had been carried out on the Lake Street Line in April 1948 and had been deemed a success. The next two lines to receive A/B service were the Ravenswood Line and the North-South Route as seen here. The revision to service also closed a total of 23 low-use stations on these lines, which also helped to improve service times.

The map goes to great lengths to explain the new patterns, with very clear explanatory text which details the system and its hours of operation. The idea of “speed” is not so subtly reinforced by the appearance of Hermes/Mercury on the front cover, awkwardly transporting a train along through the clouds at a godly pace.

More information on the history of Chicago’s A/B stopping pattern here.

Source: mister_scantastic/Flickr