The cab was traveling on the wrong side of the road. In fact, it was on the wrong side of the Atlantic.

More than a decade after the last Checker cab was taken out of service in New York City, a small collection of the unmistakably boxy yellow cars, replete with mechanical meters, rate information decals and left-side steering wheels are now seen on the streets of London.

And just as some Checkers motor on abroad, a collection of antique London black cabs, bearing the conservative, even dowdy styling reminiscent of an old tuxedo, have found a home in New York.

Behind these cab-out-of-water foreign fleets is the relationship between two men from vastly different backgrounds but with overlapping personal and business interests, identical yet inverse automotive niches and a friendship that spans 3,500 miles.

For more than a decade, the two men, Ray Tomkinson of Manchester, England, and Alvaro Gallego of Queens, both taxi entrepreneurs with a love of vintage vehicles, have swapped these signature vehicles of their homelands — along with modern models, parts and other taxi paraphernalia — across the Atlantic Ocean, typically on barter.

"Basically no cash changes hands," Mr. Tomkinson said. "We were just paying for each other's shipping, and the cabs were going across the Atlantic backward and forward."

Mr. Tomkinson, who took over his family taxi company in Manchester in the early 1970s, has amassed a large collection of antique cabs from around the world. Mr. Gallego is a Colombian immigrant and former cab driver who has run a company that specializes in taxi meter repairs for 38 years.

In addition to bolstering personal collections, their cars are rented out for film shoots and promotional campaigns — like when British Airways hired one of Mr. Tomkinson's Checker cabs to drive around London and one of Mr. Gallego's black cabs to drive around New York to advertise flights between the two cities.

The two men have done business for about 12 years but have never met. For all the cabs they have shipped across the ocean — more than two dozen they estimate — neither man has ever made the trip himself. "I consider him my friend," Mr. Gallego said. "We've been so long together talking about taxis, business. We have a passion for what we do."

There is something fitting that in the world of intercontinental antique vehicle swapping, it would be these two models passing each other at sea.

The designs of both the Checker and black cabs — largely unchanged since the 1950s — have come to symbolize their home cities, their distinctive curves adorning all manner of gift-shop knickknacks. And both were made explicitly to be taxis — purpose-built, according to the industry lingo — with roomy back seats large enough to comfortably hold five people thanks to the rear-facing, flip-down jump seats.

But the bulk that made the cars so endearing to generations of riders also drove up costs and drove down fuel efficiency. Once the most common taxi model in New York, the Checker ended production in 1982 after it proved unable to compete with converted passenger vehicles like the now-ubiquitous Ford Crown Victoria. The final Checker retired from service in New York 17 years later. The black cab still accounts for an overwhelming majority of the London taxi fleet, though it too has been pressed by new models, stoking the fear that it could go the way of the Checker.

Fans, however, say the vehicles have timeless qualities. "Both are strong and good cars," Mr. Gallego said. "They've been doing what they've been supposed to be doing for so many years, moving people from A to B in a safe way, in a roomy way."

He and Mr. Tomkinson developed an interest in antique taxis by starting with their own domestic variety.

After years of acquiring and restoring old British cars at his garage in Manchester — including a 1911 Renault that he believed was the oldest taxi in England — Mr. Tomkinson, now 62, began renting them out for period movies and television shows. About 15 years ago, a producer asked him for a New York cab. "I'd exhausted my interest with the English cab," Mr. Tomkinson said. "So I diversified."

Mr. Gallego, 64, had nurtured an interest in old taxis since first sitting behind the wheel of a cab four decades ago, still new to America and fresh off a stint as a military policeman. His skill at tracking down old parts and models led other collectors to enlist his help.

After a period of financial turmoil during which his meter shop was ordered to pay back taxes and he declared personal bankruptcy — "My life has been a roller coaster," he explained with an rueful laugh — Mr. Gallego started a second business, Taxidepot, renting old cabs and antique car equipment to movie and television producers.

Eventually — both estimate it was about 12 years ago — Mr. Tomkinson was introduced to Mr. Gallego as someone who could handle his business in the United States. At first, Mr. Tomkinson paid cash for the vehicles that Mr. Gallego helped procure.

That work led to Mr. Gallego inquiring about the feasibility of sending London cabs to New York. Soon they were working out trades, paying for each other's shipping costs. "I would get a taxi, he would get a taxi," Mr. Gallego said. "He'd say: 'Get me four Crown Victorias in nice condition; you get a London cab.' "

"If you buy in a foreign country, it's good to have eyes and ears, someone you can trust to buy it for you," Mr. Tomkinson said.

The two men often refer business to each other, like when movie producers in London approached Mr. Tomkinson about obtaining 22 modern New York cabs for a film shoot. Without such a stash on hand, he gave the job to Mr. Gallego, who shipped the taxis over, including three extra cabs for Mr. Tomkinson as a commission.

They send shipments as needed, sometimes surprising the other with an old license plate or rooftop advertisement. Last month, Mr. Tomkinson received a Checker throttle cable to replace one that had broken.

Each speaks with pride about the Checker and London cabs they have traded for. Driving the foreign vehicles on their local roads, they say, never fails to draw attention.

"Its good to see these old cabs not retire," Mr. Tomkinson said. "They're still earning a living somehow."