Many different types of hybrid cars exist, but the most common definition for a hybrid car involves a vehicle that uses a combination of gasoline and electricity to operate. As a more general definition, a hybrid car is any type of car that uses more than one power source to move the vehicle. Vehicle manufacturers are testing a variety of cutting-edge ideas and designs with hybrid vehicles.
In general, vehicle manufacturers promote their hybrid cars as environmentally friendly. The hybrid cars typically deliver better gas mileage than a standard gas-only engine vehicle, and, by using less gasoline, such hybrid cars don't generate as many harmful emissions when traveling over the same distance as a gas-only vehicle. In addition, when running from electricity instead of gasoline, hybrid cars create no emissions, making them a good option for protecting the environment. However, some questions exist about whether the batteries in hybrid cars will cause significant long-term damage to the environment.
Several of the major vehicle manufacturers worldwide already make or are designing some sort of hybrid car for consumers. Most such vehicles contain the word "hybrid" in the vehicle's name. For example, Toyota, Honda, Ford, and GM all have made hybrid cars in recent years. The Toyota Prius Hybrid was the first commonly produced hybrid vehicle for consumers. It was sold in Japan beginning in 1997 and worldwide beginning in 2001.
Most of these consumer-level hybrid cars consist of a similar design, where a gas engine powers the vehicle much of the time. However, when the driver engages the vehicle's brakes, the hybrid vehicle collects the power generated by the friction of the braking, called regenerative braking, and stores the power in a series of batteries. Under certain driving conditions, the hybrid vehicle then shuts down the gas engine and operates from the electrical power stored in the batteries. At other times, the vehicle will use both power sources simultaneously. These types of hybrid cars try to maximize gas mileage when determining how to propel the vehicle.
Another type of hybrid vehicle, initially proposed by GM, would only contain an electrical engine. A driver could plug the vehicle into an electrical outlet, storing electrical power in a series of batteries. This type of hybrid car's engine would run from electrical power for as long as possible. When the electrical power is exhausted, the vehicle then would use a small gas generator to create electricity to continue powering the engine.
Beyond those popular types of hybrid cars made for consumers, there are some other non-consumer types of hybrid vehicles that are already in use. For example, some trolley buses in large cities can alternate between running from a diesel engine and by using power from an overhead electrical line. Another type of bus can operate from two distinct fuel sources, such as gasoline and natural gas. This type of bus uses two different fuel systems to prepare the fuel for a single engine. Some other hybrid cars make use of a mixture of gasoline and compressed air to propel the vehicle.