Hybrid cars are increasingly popular with celebrities and those who want to demonstrate their commitment to a cleaner environment. Hybrid owners' clubs may be springing up all over, but buyers and policy makers need to understand that these vehicles are not a good choice for everyone. A number of misperceptions cloud the issue:

First among them is the idea that hybrid cars will save the environment. Overall, hybrids generally have a smaller environmental impact than regular cars. Much of the potential advantage depends on the buying and driving habits of the owner.

The manufacturing and production of hybrids generate slightly more greenhouse gas emissions than the production of similar traditional cars.  Hybrids recoup this added environmental impact over the lifetime of the vehicle because emissions are lower during normal operation.  As a consequence, the overall environmental benefits of hybrids would seem to increase as more miles are driven.  But if these miles are on the highway, the emissions savings are not that great.

Hybrids like the Toyota Prius and the 2006 Honda Civic Hybrid only engage the electric motor at low speeds.  In highway driving, these cars use the gasoline engine. Most stop-and-go traffic is in residential and city settings where the most environmentally friendly options are public transportation, biking, or walking as much as possible.  And there are some situations where a hybrid is simply a bad investment.

According to the Sacramento Bee, the city of Elk Grove recently purchased 21 hybrid buses at a cost of more than $400,000 each.  It turns out the hybrids, performing under stress on freeways in hot weather, shut down their air conditioning systems, leaving passengers to bake. The emissions associated with producing these vehicles won't be offset if they're taken off the road because they don't work.

A second myth is that plug-in hybrids or electric cars are even more environmentally friendly. In hopes of extending the operating range of the electric motor, many fans of hybrid cars are looking forward to mass production of plug-in hybrids or fully electric vehicles. Some owners are even modifying their hybrids to allow for plugging-in.  Some tout these options as achieving near-zero emissions - but full electric vehicles surpass even hybrids in CO2 emissions during the production process. 

After production, greenhouse gas emissions from the vehicles themselves is small, but that is only part of the story.  The electricity used to charge the vehicle must come from somewhere, and in most of the country that is a coal-fired power plant, not known for low greenhouse gas emissions. The only way the plug-in strategy significantly reduces net emissions is if the energy to charge the car comes from non-emitting sources such as hydropower, wind, or solar. 

In the future, carbon capture and storage technologies may be widespread enough that using electricity from fossil-fuel sources emits less CO2, but for the time being, plug-in cars simply move the source of emissions from tailpipe to power plant.  At the same time, if operators charge the car battery at off-peak times, some load-leveling is achieved at the power plant, which makes the plant run more efficiently.

The final misperception is this: incentives on buying and driving hybrids are a great way to encourage environmental conservation.  Beginning January 1, 2005, qualified hybrid purchases came with a federal tax credit of up to $3,150.  There is a limit of 60,000 vehicles that can qualify for the maximum tax credit, and the program is being phased out.  Many are lobbying for an extension of the tax incentives. Numerous states and cities offer incentives such as free parking or access to HOV lanes normally restricted to vehicles carrying three or more.

EPA estimates show that hybrids like the Prius emit about half the smog-producing pollutants of a comparable traditional vehicle. A traditional sedan in the HOV lane carrying three passengers emits fewer pollutants per person-mile than a hybrid car in the HOV lane carrying one person. 

At most dealerships there is still a waiting list for hybrid vehicles, and much of this demand is driven by today's high prices for gasoline.  An incentive doesn't make much sense for a product already in demand for other reasons.  Incentives may even be fostering a sense of entitlement on the part of some hybrid buyers.  The Chicago Tribune recently reported that potential buyers are expecting dealer (not factory or government) discounts and incentives on hybrid vehicles, despite the waiting list.

Hybrids certainly have their place and, if well matched to driving habits, can be a cleaner alternative to traditional internal combustion vehicles. People buying hybrids should do so with full awareness of the performance limitations, environmentally and otherwise.