Havana.– First comes the stink of diesel, then a metallic roar, and finally a tower of black smoke that tells you the "camello" –the camel– has reached your stop.

These hulking 18-wheeled beasts, iron mutants made of two Soviet-era buses welded together on a flatbed and pulled by a separate cab, have long been Havana's public transport nightmare –bumpy, hot and jammed with up to 400 passengers at a time.

But their gradual disappearance is a telling sign of change in the twilight of the Fidel Castro age. The last "camello" is expected to go out of service in Havana on Sunday night.

The camello, so named for its humped front and rear sections, is being eclipsed by thousands of new city buses from China as the government under Castro's brother, Raul, resuscitates a public transportation system on the brink of collapse.

Route M-6, running from the capital's southern outskirts uptown to the University of Havana, is the city's last remaining camello route, and municipal authorities say they have been told to pull all camellos off it this weekend.

"I think we should build a monument to the camello," said retiree Salvador Carrera, a camello passenger. "It has been an extraordinary thing."

The capital aside, camellos are far from extinct. The government has an island-wide fleet of more than 1,000, and those from Havana could be used to augment bus service elsewhere, transportation employees say.

Like those ubiquitous Detroit cars that predate the U.S. embargo, the camello is a definer of Cuba on wheels, but without the fun of a San Francisco cable car ride or the clean efficiency of the Washington, D.C. Metro.

What it lacks in glamor, it makes up for in sheer mass that dwarfs its Chinese successors. "We can carry up to 400 people. The bus cannot," lamented conductor Estela Doira. "I'm happy, also sad, because the camello handles a lot more than the bus."

At the start of a camello run one morning last week, it took just over five minutes for 75 passengers to swarm up the steep steps and through the narrow doors at the rear. Doira hung out of a window to make sure no one got stuck. The doors, thin metal with sharp edges, shut with a metallic crack that sounded sharp enough to sever limbs.

The fortunate got one of the 58 plastic seats, while the rest had to stand. Each alighting passenger paid Doira 20 centavos, less than an American penny.

Camellos have no shock absorbers, and every pothole sends a violent jolt through one's feet. At each stop more passengers crowd in –people carrying infants, backpacks, gardening tools and beer bottles stuffed with black market honey. Baby-faced soldiers squeeze in beside college students in hot-pink sunglasses and elderly men looking thin enough to be crushed in the crowd.

It's hard to work one's way on or off, and the driver in his cab can't hear people screaming, "The door! Open the door!" "Move it, companeros! Move to the front!" they yell.

With no air conditioning, the tropical heat quickly becomes unbearable, and the stench sets in –fresh sweat and body odor, mixed with exhaust and rotting food. Those seated stick their heads out of the windows.

"Only in Cuba. In other countries people wouldn't put up with so much," whispered retiree Mari Gonzalez, who was fortunate enough to snag a seat.

Cubans joke that camellos are racier than a Saturday night at the movies –full of sex and crime, pickpockets and gropers. Overheard conversations between passengers feed the onboard rumor mill: Fidel Castro is dead. No, wait, he's healthy again; he spent last weekend at the beach. The peso will strengthen against the dollar. Or maybe will be replaced with a new currency.

The camello was born in response to fuel shortages in the early 1990s, when the Soviet Union collapsed and Cuba lost its annual $6 billion in subsidies. The economy has since recovered thanks to heavy borrowing from China and nearly 100,000 barrels of oil a day from Venezuela.

Cuba is spending $2 billion to upgrade public transportation and has imported 3,000 modern buses just for the capital. The Yutongs are less sturdy than the camellos and crews are repaving streets to spare them wear and tear. Fares are double the camello's but offer far more seats and a dramatically smoother ride. Riders can climb on and off easily, ensuring faster trips.