Every day after 5 p.m. thousands of cars snake from Colon, on the Atlantic side of the Panama Canal, to Panama City, on the Pacific.

Many people who work in the Colon Free Trade Zone or at one of the big container terminals prefer to live in the Panamian capital. So they shuttle the 80 km, on the country's only toll road, between the Atlantic and Pacific Oceans.

People have always used the Isthmus of Panama, the narrowest part of North America, to get from one ocean to the other - first on foot, then on horseback and with horse-drawn carriages. A railway line was completed in 1855, allowing the transit of bulkier goods from ships on one side to ships on the other.

Much of the line, the original Panama Railroad, is now underwater. The big sea faring ships sail over it as they proceed through the Panama Canal and Lake Gatun, which was created by damming the Chagres River.

The 19th century headquarters of the Panama Railroad, which directed inter oceanic rail traffic across the Isthmus of Panama (then governed by Bolivia), were in a building that today is the Hotel Washington. The fastest and most convenient route linking San Francisco and New York in those days was via Panama.

The Panama Railroad proved so successful that at one time it was the highest-priced stock on the New York Stock Exchange. In 1913, a year before the Panama Canal began operations, it transported nearly three million passengers and more than two million tons of freight. Without the railway and its transport capacity the canal could never have been built.

Passenger service on a modest scale resumed just six years ago. A single train, luxuriously outfitted, travels from Panama City to Colon in the morning and returns in the evening. Travel time is 57 minutes - the quickest way to get from one ocean to the other.

Driving the distance can take two hours or more as the road is perpetually congested. And ships using the Panama Canal need about eight hours, after waiting for days to enter the waterway.

As soon as the train leaves the station, laptop computers are flipped open. For traders from the Colon Free Trade Zone, the air-conditioned coaches are an ideal place to work out final details with buyers and partners, to compare prices, and to make offers.

Through large windows they can enjoy the picturesque tropical rainforest, which continually opens up to reveal Lake Gatun and the big ships gliding on it. In some places the train seems to glide through the middle of the lake as it passes along an embankment just above the water's surface.

The train has first-class coaches only, all of which have bar and snack service. There is also a restaurant coach. Open-air viewing decks allow passengers to get a feel for the tropical heat and humidity. A one-way trip costs $22 (17 euros).