Veteran St. Paul actor and singer Kathleen Humphrey has sung or appeared in productions with all the big shows in town: the Minnesota Opera, Minnesota Orchestra, St. Paul Chamber Orchestra, Guthrie, Chanhassen and Theatre de la Jeune Lune.

But by far the biggest audience she’s ever played before is Twin Cities straphangers.

That’s because Humphrey, who is also a voice actor, is the voice of light rail.

Long before the Blue Line opened in 2004, Metro Transit hired Humphrey to make all of the recorded messages heard in the train and on train platforms. They include stop announcements, how to use the automatic ticket machines, where to exit in case of a crash, warnings to keep an eye on your possessions, the imminent arrival of a train and one asking that handicapped seats be left available to those who need them.

Metro Transit continued to use her as the voice of the new Green Line as well, which means that more than 60,000 riders hear her every day intoning important information like: “Would you like a receipt? If no, press I. If yes, press J. To go back to the previous screen, press E,” or “Connect here to these bus routes: 16 and 67.”

“I tell people they can’t smoke on the platform,” Humphrey said. “I say, ‘This train is no longer in operation.’ ”

Humphrey also does voice work for Northstar Commuter Rail and Minnesota Valley Transit Authority, meaning her voice has been the narration for well over 100 million individual trips in the region.

She said she won the part of the voice of light rail through an audition process in which both men and women applied. The goal is a voice that’s “warm, sort of neutral, authoritative, calm, reassuring,” she said.

“There is an air of authority when she speaks,” said Laura Johnson, owner of NUTS Ltd., the Golden Valley talent agency that represents Humphrey. “There is an intelligence that comes across in her delivery style.”

Maybe that’s why Humphrey’s other voice work specialty is recording medical-related messages on videos and phone lines for clients such as the Mayo Clinic, Medtronic and the Minneapolis VA.

“I’m pretty good at pronouncing different medical terms and drug names,” she said.

It might be more glamorous to appear on stage, as she did last month singing in the role of Nettie Fowler in a production of “Carousel” with the Minnesota Orchestra.

But Humphrey, who also works as a server at Pizzeria Lola in Minneapolis, said voiceover work is “very well compensated.”

And if you’re just going to be in a recording studio saying, “This is the Blue Line train to Target Field station,” you don’t have to wear a costume.

“It’s a very interesting gig,” she said. “It’s just a really nice, ongoing client.”

“I’m always pushing for more light rail,” she said. “I’m glad they’re expanding. Not just because I’m doing the voice.”

Humphrey said some people think her recorded messages are computerized. She said even acquaintances don’t always recognize that it’s her voice when they ride the train.

“They say, ‘Oh, of course,’ ” when she informs them, Humphrey said.

On a recent Green Line ride, commuter Ian Smith gave a good review of Humphrey’s performance.

“It has those intonations, that it’s always there, like a flight attendant. They’re trained to calm people,” Smith said. “Metro Transit can be really stressful.”

Richard Chin can be reached at 651-228-5560. Follow him at twitter.com/RRChin.