Making music on Metro Mex

The young mums cradling children, elderly ladies with hand-woven shopping bags, and briefcase-clutching businessmen have all managed to nab a seat.

I'm standing near the train doors, rubbing shoulders with teenage punks, gel-haired labourers, pouty university students and a buxom lady who's passionately chewing the ear off her boyfriend.

I've still got 13 stops to go. On most subways, this would be a rather boring, clock-watching ride.

However, the Mexico City Metro is definitely not your average subterranean transport system.

As the train rattles along, and conversation levels among Chilangos - the nickname for the capital's residents - build to a noisy crescendo (there's no London-style reticence here), Vivaldi's Four Seasons starts drifting around the carriage.

Initially, I think the music's coming from the train speakers. Then it gets louder. And louder. Then the volume suddenly drops. A chubby young Mexican, baseball cap on back to front, is shuffling to the other end of the carriage, waving CDs and chanting: "Diez pesos! Diez pesos!" ("10 pesos! 10 pesos!" - about 75¢.)

Wedged into his backpack is a set of vibrating speakers, out of which Vivaldi is soon replaced by Mozart. Then we're treated to Verdi. And Wagner. The classical compilation is a hit.

The man makes four quick sales and hops off at the next station, his bum bag rattling with coins, the sound of Beethoven floating off into the distance.

I look out the door, and see him climbing into the next carriage while another character with speakers strapped to his back boards ours.

He's offloading CDs of Mexican mariachi classics, accompanied by a friend - a chirpy old soul with a grey moustache, who's selling 1980s American pop music.

The most affecting vendor comes next; a heavily pregnant young woman who appears as if she's about to drop. Her facial expression is as melancholic as the Spanish tunes she's playing.

When she glumly exits the carriage, without making a sale, I'm struck by pangs of guilt.

My conscience is also bothered by a woman, in her 80s, hobbling along with a walking stick, crooning out a song and pushing out a plastic cup pleading for tips.

She's followed by two blind, doddery male buskers - a guitarist and a harmonica player.

Not all Metro vendors earn their pesos through music. Others make impressively vigorous sales pitches for chest rubs, face paint, lollipops, lip balm, toys and books.

Strikingly, I see no idle beggars on what is Latin America's busiest subway (used by 1.5 billion passengers annually, apparently).

When we reach my stop, I'm almost sad to get off.

At just three pesos a ride (about 21¢), this isn't just the cheapest, shrewdest way to avoid the traffic jams that clog the overland arteries of Mexico City.

It's a cultural sight in its own right.