Turnstile

In addition, a turnstile can restrict passage only to people who insert a coin, ticket, transit pass, security credential, or other method of payment or verification.

[1][2] They may have been used from the early modern period to control access to toll roads, and retail streets, the Holborn Great Turnstile appearing in 16th century literature[3] Turnstiles were adopted as a means to control access to building and amusements during the 19th century, with many sports stadium and swimming pools installing them,[4][5][6] patents for improvements to the concept being granted to manufacturers.

[11] Turnstiles are used at a wide variety of settings, including stadiums, amusement parks, mass transit stations, office lobbies, airports, ski resorts,[note 1] factories, power plants and casinos.

On the other hand, physical barriers become a serious safety issue when a speedy evacuation is needed, requiring emergency exits that bypass any turnstiles.

The ticket barriers on the London Underground and some busy UK railway stations have to be open if either the gates are unmanned or in an emergency.

At some locations where luggage is expected, a line of turnstiles may be entirely formed of wide aisle gates, for example at Heathrow Terminals 2 & 3 Underground station.

A disadvantage to this type is people can "jump the turnstile" as happens commonly[citation needed] on the Moscow Metro and other mass transport systems in Russia.

Optical turnstiles generally use an infrared beam to count patrons and recognize anyone attempting to enter a site without a valid entry pass.