HANOVER, Germany -- ATDynamics says it's introducing its TrailerTail and a shorter Eco50 product in Europe, pending a change in the European Union's length limits which currently preclude their use.

The San Francisco-based company meanwhile said the longer device, called EcoTail in Europe, was tested by TNT Express in The Netherlands and showed a 6% savings in fuel by cutting air drag at the rear of trailers.

"TrailerTail is a proven technology which can be implemented immediately by the international community," said Andy Smith, the company's founder and CEO, during the IAA show this week in Hanover, Germany.

If used on the 2 million long-haul semitrailers now used in Europe, it could save 5 billion euros ($6.5 billion) in fuel per year, he added.

Like the folding-panel TrailerTail used on semitrailers in the U.S., the EcoTail is 122 centimeters (4 feet) long, which EU trailer-length regulations do not permit. But a proposed directive from an EU commission would allow an exemption for aerodynamic devices.

A similar dispensation is now in effect in the U.S., where up to 5 feet may be added to a trailer's length for a fuel-saving aerodynamic improver, Smith noted. EU Directive 97-27 wouldn't be that generous, but would allow the 50-centimeter (1.6-foot) NanoTail, which he calls Eco50 in Europe.

Eco50 offers about half the benefits of the longer design, which include fuel savings and emissions reductions. So it takes about twice as long, or six to 24 months, to return its investment, he said.

The fleet test in Holland was done under permit with the help of Ephicas, a European aero firm that ATDynamics is partnering with, Smith said. The test ran for five months in regular service at top speeds of 80 kilometers (about 50 miles) per hour, and showed savings of 1.65 liters per 100 kilometers, or 7 U.S. gallons per 1,000 miles traveled.

"Savings on the fuel cost is an interesting business case, but also helps us reach our goal of decreasing CO2 emissions of our operations," said Irma Blanke, director of operations & services for TNT Express Benelux. The test also showed that the folding panels posed no problems to drivers or operations.

TrailerTails are now on more than 5,000 trailers in the U.S. and Smith said he hopes to have 20,000 in use by 2014. He quoted the manager of one user fleet as saying that the devices save 0.4 mpg in everyday service.