A handrail in living quarters
A handrail aboard the Fortunate
A railing or rail was a long bar that protected against falls from high heights. The most common use of railing was the handrail, which was a support bar used for resting one's hands on in instances such as climbing a set of stairs.
The bridge aboard the NX-class Enterprise NX-01 featured a handrail behind the captain's chair and in front of the situation room. (ENT: "Terra Nova", "The Andorian Incident", "Civilization")
In 2151, Trip Tucker noted that if one were to rest one's hands on the handrail of a lift in Enterprise's engineering section during the lift's operation, one's fingers might be amputated. (ENT: "Unexpected")
Handrails were also found in engineering and in the launch bay aboard Enterprise. (ENT: "The Andorian Incident")
Handrails were also used aboard Y-class Earth Cargo Service freighters where they were placed at the catwalks in the cargo modules. (ENT: "Fortunate Son")
In 2152, Trip Tucker sarcastically offered to polish all the handles and rails in Enterprise's engineering while the ship unexpectedly changed course for the Pernaia system. After Jonathan Archer gave him a look, he decided to purge the impulse reactors instead. (ENT: "The Seventh")
Later that year, while traversing a cave with Travis Mayweather and Malcolm Reed, Tucker commented that the last cave he visited had handrails, a gift shop, and a snack bar. (ENT: "The Breach")
In 2369, Quark berated Rom for returning a patron's full currency pouch, giving him the punishment of polishing every rail in Quark's. Soon after, spying a lazy Nog, Rom passed on the punishment to him. (DS9: "The Nagus")
The living quarters of the Species 8472 member representing Valerie Archer features a handrail next to the stairs. (VOY: "In the Flesh")
In 2399, a Romulan death squad operated near the Starfleet archives in San Francisco but inexplicably did not show up on the security feed. Later, director of Starfleet Security Commodore Oh looked at the footage and wondered if she recognised disruptor fire relected in a handrail. (PIC: "Remembrance", "Maps and Legends")