3-wheel. A vehicle with only three wheels. There are two common orientations: 1 wheel in front and two in back (like a trike), and so-called reverse-trikes, with 2 wheels in front and one in back, like the Aptera. In either case, the vehicle is typically classified legally as a motorcycle, and is thus not required to pass automotive safety tests. This makes the vehicles much cheaper to develop and bring to market. Unfortunately, the untraditional looks of this type of vehicle have meant that one has never succeeded in the market place – it remains to be seen if a market can be found for them.

AXP: The Automotive X Prize, a multi-million dollar prize for the winner of a 100 MPGe staged race. Official Website. The rules try to encourage vehicles that consumers will want, and be able, to buy.

CAFE: The Corporate Average Fuel Economy, a US law which regulates the sales weighted average fuel economy of consumer vehicles. Official Website. Now set to rise to 35 MPG by 2020, from 27 MPG in 2008. Most countries have much stricter laws on fuel economy. California is suing the EPA in order to regulate CO2 emissions, which will directly require higher fuel efficiency than CAFE does.

CO2e: Carbon Dioxide Equivalent. A way of measuring the climate change impact of a vehicles emissions. For the AXP, all vehicles must emit less than 200 grams/mile CO2e. You can check out all the details in a spreadsheet that the AXP has provided. One notable implication of this requirement is that pure electric vehicles will be required to achieve at least 132 MPGe, because charging from the national grid averages 200 grams/mile at 132 MPGe.

E-REV, or RE-EV: Extended Range Electric Vehicle. Take an EV, and add a portable electric generator. The generator does not directly drive the wheels, but instead only generates electricity, which can be used to drive the electric motors and/or charge the batteries. This is sometimes also called a “series PHEV”.

EV, BEV: (Battery) Electric Vehicle. A car which runs on electricity, typically stored on-board in a battery. These cars are mechanically much simpler than traditional vehicles, cheaper to fuel, and easier to maintain, but because of the state of the art in batteries, they are often more expensive and have limited range and/or top speed. Tesla been been trying very hard to dispel these market perceptions.

Hybrid: a vehicle with multiple power/drive systems. Typically a hybrid has a gasoline engine and an electric motor, but there are also diesel hybrids (with a diesel engine + electric motor) and hydraulic hybrids (with gasoline engines and hydraulic motors, commonly used for regenerative braking). It is even possible to use compressed-air as the second power source.

Li-ion, Lithium: A type of battery which is lighter, more powerful (more watts) and more energy dense (more kWh/lb and kWh/inch^3) than previous batteries such as lead-acid or NiMH. Consumers are familiar with the technology from laptops and cell phones, but in larger formats the safety concerns (most lithium batteries are subject to thermal runaway leading to explosions) and cost have so far prevented wide-spread application. Many startups are claiming to have safer and/or cheaper lithium batteries for use in automotive applications.

MPGe: Miles Per Gallon Equivalent. From the Automotive X Prize (AXP) rules, this is a way of translating the consumption of non-gasoline “fuel” usage into terms comparable to gasoline usage. The energy in the fuel is calculated at “the pump” and compared directly to the energy contained in gasoline at the pump. For instance, for electricity, 1 kWh contains 3,412 BTU. One gallon of gasoline contains 116,090 BTUs, so 34.02 kWh of electricity is “equivalent” to one gallon of gasoline. This is very favorable for electricity, since a vehicle can use electricity substantially more effectively than gasoline. In a similar manner, it takes only 0.897 gallons of diesel fuel to be equivalent to a gallon of gasoline – lessening the advantage that diesel otherwise has. You can check out all the details in a spreadsheet that the AXP has provided.

PHEV: Plug-in Hybrid Electric Vehicle. Imagine the Prius, but with a larger battery and an ability to plug the car unto the wall to charge the battery up. This terms owes a lot to CalCars, who have been promoting them for years and are at least partially responsible for the announcements in 2007 & 2008 by major carmakers that these vehicles are finally on the way. The big benefit of PHEVs is that the electricity obtained from the grid displaces petroleum (gasoline) usage, making it possible to get 100+ miles per gallon of fuel (using instead electricity). They are sometimes controversial because electricity comes partly from coal, a very dirty fuel. A “parallel PHEV” is one in which the internal combustion engine AND the electric motors are both capable of driving the wheels directly. A “series PHEV” is more commonly called an E-REV; the internal combustion engine does not drive the wheels directly, it only generates electricity.