Vicki Sayers arrives at London's Westminster tube station with her guitar slung over her shoulders like a backpack, pulling her amp on a dolly. She sets up in a corner of the cavernous subway station and plays John Denver's "Take Me Home, Country Roads" as three judges and a crowd of commuters listen.Sayers, a high school senior from outside London, is among more than 300 musicians vying for up to 100 coveted licenses to play on the Tube, the world's oldest subway system. Transport for London, which operates the Tube, has been holding auditions since 2003. It's a way to ensure quality and control the number of buskers. Each year, musicians provide more than 100,000 hours of live music in stations here.For Sayers, who hopes to become a professional musician, it's a way to practice her craft, make some money and entertain a potential audience that numbers in the millions."I'm really trying to get more into [the] London music scene," says Sayers, who wears jeans and a black sweatshirt. She lives in Berkshire, about 50 miles west of the British capital. "I think busking is a great way to do that."Sayers is going up against a number of competitors this morning in a competition that could be called Tube's Got Talent. This includes Tony Moore, who played keyboards in an English rock band in the 1980s and sings Elton John's "Rocket Man" for his audition; Miles Sutton, a university student, who plays a jazz number on his guitar; and Tom Ryder, 27, from Essex, who plays an affecting acoustic version of Chaka Khan's "Ain't Nobody." At 17, Sayers is already a veteran of London's busking scene; her poise shows as she gives a haunting rendition of the ode to the simple life in West Virginia. In the past, she's played beneath the escalator at London's Waterloo train station — the country's busiest – which offers big crowds and little competition. Sayers explains the appeal of Waterloo – a prime busking spot – through another passion of hers: economics."There's a theory called scarcity," she says. "When you play in London Waterloo, you normally have a licence and you have to book [space in advance]. I find that a lot more people stop and listen and enjoy what I'm playing because there's not really anyone else around playing."Sayers says in two hours at Waterloo, she can make nearly $80 in tips.Playing in London's Tube and rail stations is not for the faint of heart. Tim Frasier, a songwriter who is serving as one of today's judges, says landing a Tube license takes grit, grace and presence. "We're looking for people to almost be having a little bit of a suit of armor when they're playing," he says as a subway train rumbles beneath. "This is not an open mic night. This is not playing for their friends. This is playing against a lot of background noise. So they have to be quite tough and friendly."Some big British stars got their start busking, including Ed Sheeran, George Michael and Rod Stewart. Buskers on the Tube play all kinds of music, from classical to blues. As the music echoes along the subway's tile walls, it can provide a pleasant surprise or a soothing distraction to commuters, especially in a city that's suffered three terrorist attacks in the past five months."The other week, we were up here and there was a man playing steel pans," said a woman named Kay, 39, who was watching the auditions and down from Tottenham. "If you're nervous about travelling and stuff, sometimes it makes you feel distracted and relaxed. So it's handy to have them around."Another one of today's contestants, Marco Felici, sings Whitney Houston's "I Wanna Dance With Somebody (Who Loves Me)." He has been trying to get a tube busking license for eight years. "It is extremely competitive," says Felici. "You have some really young kids who deliver some great stuff. At 36 years old, I have to compete with that. Not getting any younger."When he isn't vying for a license, Felici also busks on sidewalks where tourists routinely make requests. "They will go: 'Wonderwall! Play Wonderwall!'" Felici says wearily. "So, you do it; you can't be too picky about things when your income depends on that."After this morning's auditions, the judges see one clear winner. "I've got to say young Vicki — 17-year-old Vicki — was absolutely amazing," says judge Rita Campbell, a singer-songwriter. "Loved her; she connected."But there are many more auditions to come, and the hopefuls won't learn their fate until late September. Sayers isn't wasting any time. She packs up her amp and guitar and heads back out to busk on the sidewalk in the shadow of Big Ben. Copyright 2017 NPR. To see more, visit http://www.npr.org/.