There are three types of electric railway transition: open, shunting, and bridging, open being the first developed and bridging the last. Bridging was the most commonly used scheme in later days (particularly with GE cam control of the 1960s/70s etc). The diagram is an extremely simplified version of bridging (doesn't show the external resistance), and with it you have to go through transition at precisely the right moment to avoid sneak currents.