Skip-stop

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Skip-stop is a public transit service pattern which reduces travel times by not having all vehicles make all designated stops along a route. The transit operator designates stations as either major or minor, typically by ridership. All vehicles stop at the major stations, but only half stop at the minor ones, which are given different designations such as "A" and "B". In bus operations, skip-stop refers to a stopping pattern where buses do not stop at every block, typically in a central business district, which similarly reduces travel time and crowding at boarding locations.

Since one rail vehicle can only pass another by using an additional track, skip-stop reduces overall travel times without any additional investment in infrastructure. Express services, where trains skip many stops along a route, require either careful scheduling or places for faster services to pass slower ones. Rapid transit systems normally run too frequently for scheduling to offer a solution, and in some systems there is no place for the slower train to pull aside for the faster train to pass. Skip-stop reduces some of the increased travel time resulting from more passengers boarding and leaving vehicles. Rail skip-stop is normally employed during busier travel hours; trains make all stops during off-peak hours, such as evenings and weekends.

In some systems, such as the New York City Subway, these are considered as two separate services (J/Z and the former 1/9), as if the two services were separate lines instead of two different stopping patterns on the same line. On other systems, like the Southeastern Pennsylvania Transportation Authority's lines, they are distinguished by lights on the train, and stations skipped by half the trains are designated "A" and "B" stations depending on which trains stop there. Chicago's CTA elevated system used skip-stop service from the 1940s until the early 1990s, at which point all-stop service patterns replaced skip-stop service. This was done to reduce waiting times for passengers riding to or from "A" and "B" stations who could only take half of the trains. It also eliminated the need for a train transfer for passengers riding from an "A" station to a "B" station which required a transfer at an "AB" (all trains stop) station to complete their trip. Further, the system was simpler to use for new riders and visitors.