Photos: Honda FCX Concept fuel cell vehicle

The Honda FCX Concept has a top speed of 100mph, and while driving the car around the racetrack we found it to be a smooth ride due to the absence of upshifting or downshifting. Throttle response is at least as quick as that on internal-combustion-engine cars, and torque is plentiful even at low rpms thanks to the car's 95kW electric motor.

In keeping with the futuristic interior of the car, the FCX Concept's shifter takes the shape of a black plastic paddle, which lets the driver shift-by-wire, engaging gears via an electronic, rather than a mechanical-control interface.

The only emissions from the Honda FCX Concept are water and heat.

Similar to all hydrogen fuel cells, the one in the FCX works by combining compressed hydrogen with oxygen from the air to create electricity and water. The vertical orientation of the stack in the FCX enables water to drain out of the fuel cell more efficiently, thus reducing the space required for flow channels.

With its swooping roofline and low front overhang, the FCX Concept has futuristic styling to match its next-generation propulsion system. A smaller fuel cell stack, built into the central transmission corridor of the car rather than under the seats, enables the body to sit lower to the ground than on previous FCX models.

The fuel cell stack in the FCX Concept is 20 percent smaller and 30 percent lighter than the current FCX FC stack, and 70 percent lighter than Honda's original fuel cell stack (pictured).

Honda showed off its latest hydrogen fuel cell vehicle this week at Laguna Seca racetrack in California. The FCX Concept builds on technology developed in Honda's previous fuel cell vehicles and is scheduled to be put into production in 2008. Due to its compact, vertically mounted fuel cell stack, the car's designers had the freedom to create a stylish, aerodynamic sedan with lots of interior room.

The FCX Concept runs on compressed hydrogen. Its fuel tank, which is located underneath and behind the rear seats, has a capacity of around 4kg of hydrogen compressed to 5,000psi--enough to take it 270 miles on one fill-up. Fueling infrastructure is likely to be one of the biggest challenges in the rollout of hydrogen cars over the next few years.

The Spallinos from Redondo Beach in California are the first family in the United States to use a hydrogen-powered car for day-to-day transport. The family has leased a previous-generation Honda FCX since June 2005 and uses it for commuting, shopping, and everyday errands.

The FCX Concept features a cab-forward design, giving rear passengers plenty of leg room. The car's interior upholstery and door linings are made from Honda Biofabric, a fuzzy wool-like material that is produced from a combination of corn and other petroleum-based ingredients. Its reflective plastic dashboard is more ornamental than useful and is likely to be replaced by a more functional arrangement in the 2008 production model.

To monitor the FCX Concept's fuel and performance, the driver is faced with a concave instrument panel displaying a kaleidoscope of multicolored virtual gauges. Among these, a circular display expands, contracts, and changes color according to the level of hydrogen being used at any one time. A green semicircular power meter on the left of the instrument cluster illuminates in blue to indicate the amount of power drawn from the fuel cell, and in green when the car is running on battery power. On the right-hand side, a fuel gauge displays the level of hydrogen in the tank.

In addition to its fuel cell stack, the FCX Concept uses regenerative braking and deceleration to charge an onboard lithium-ion battery that assists the car's electric motor in periods of high acceleration. The car's motor, which has an output of 95kW and drives the front wheels, is mounted coaxially beneath the hood.