Every mode of transportation has its disadvantages. Cars crowd the streets, pollute the air and are hard to park. Trains fill up during rush hour and often have inconvenient schedules. And airplanes aren't practical for short trips around town.

Some researchers are promoting RailCabs as the vehicle of the future. These driverless, computer-controlled cars take passengers and cargo directly to their destinations without stops or transfers. They can travel in convoys to save energy and then peel off from each other as each car heads to a separate destination.

Small version already been developed

Under development for a decade, researchers at the University of Paderborn have a prototype of the RailCab. A test track has been built near Paderborn, a city in the western German state of North Rhine-Westphalia. Since 2003, slightly smaller-than-life RailCabs have run on a 600-meter test track near the University.

Researchers have declared the prototype a success and say they're ready to test their revolutionary trains under real-life conditions. The engines, chassis and rail technology are ready for production.

"These are not toys," Professor Joachim Lückel, who started the project, told the Associated Press.

More money needed

However, a full-sized prototype has not been tested as yet. That is expensive, Lückel said, adding that 11 million euros have already been invested in this project and an additional 20 million euros are needed to build a full-sized prototype.

The cars would travel on normal rails, but would use a so-called linear motor, which needs little maintenance. They would use magnetic fields to accelerate, similar to the Transrapid train, but would otherwise run on tracks.

Adapting tracks to fit the RailCab would cost 800,000 euros per kilometer. New tracks would cost 3.5 million euros per kilometer. That's a lot of money, but much less than it costs to build new high-speed train tracks, Lückel said.

Additionally, turnouts would need to be added so that RailCabs could leave convoys. But the entire system would still need to be compatible with trains.

The RailCab would revolutionize transportation of both people and cargo, Lückel believes, making it much more efficient. The enormous flexibility of a RailCab system would make the costs worth it, Lückel said.

Not everyone is a fan

But not all experts share Lückel's enthusiasm.

"Converting tracks is more expensive than building a second regular track," said Edmund Mühlhans, an emeritus professor and rail expert at the technical university in Darmstadt.

Also, stretches of track exist which run at capacity and don't have additional space to accommodate RailCabs. If RailCabs had to detour around these tracks, they would not be as efficient, Mühlhans said.

Mühlhans also envisions technical problems. Linear motors are noticeably less efficient than conventional locomotives. The large number or RailCabs that would be needed would mean more inspections, maintenance and repair, he said.

"Despite all the advantages that the inventors have always predicted, cab trains have never made it past the pilot project stage," said Mühlhans.

Lückel said the time has come for the project to move forward. If it doesn't happen soon, Lückel worries that his specialized researchers could get disillusioned with the project and go to work in private industry.

"We need government support," Lückel said.

A few wealthy customers from the Middle East have apparently made discreet inquiries. But for now, the project is spinning its wheels.