President Obama’s comprehensive plan to cut vehicle emissions and raise fuel efficiency standards raises a number of questions about how it would all work.

The proposed new rules, announced Tuesday, will begin to be enforced in 2012. The goal is to ensure that cars and trucks sold in America will be nearly 40 percent cleaner and more efficient by 2016.

Here are some questions and answers about the plan.

How will the new rules work?

The plan will not prescribe the size of cars and trucks, but it is designed to spur innovation and resourcefulness by raising the energy-efficiency bar for all sizes and types of vehicles. There will be new requirements for tailpipe emissions of carbon dioxide and for gas mileage. By 2016, passenger cars must average 39 miles per gallon and light trucks 30 mpg. Overall, vehicles that are sold in America must average 35.5 mpg in seven years. At present, the average vehicle gets 25-28 mpg.

How much oil will be saved?

By White House calculations, the new guidelines will save 1.8 billion barrels of oil by 2016, reducing this country’s dependence on international and domestic oil.

Will I be forced to ditch my old, inefficient clunker?

No. The rules are for new cars only.

What new kinds of cars are likely to be offered in the U.S. under the new standards?

Carmakers will probably roll out more lightweight trucks, cars with smaller trunks and a wider variety of hybrids and other nouveau-fuel models. The new-and-improved vehicles will be required to be cleaner and savvier in their use of fuel. The Obama administration estimates that new standards – from these rules and from previously approved rules – will add about $1,300 to the price of a new vehicle by 2016.

Why is this happening now?

Because the government is providing loans to help U.S. automakers survive, the Obama administration is in the driver’s seat to make these demands of automobile manufacturers. Fourteen states – including California – and the District of Columbia have been bucking for higher standards. And the Supreme Court has ruled that under the Clean Air Act, the Environmental Protection Agency must take steps to curtail greenhouse gases.

What has been the industry’s response?

The automobile industry says it welcomes nationwide standards. But in reality it doesn’t welcome these rules. Automakers worry the rules will be the final nail in the coffin of the American auto industry. After all, the industry was suing to stop nearly identical California standards. But it can’t oppose the federal rules because GM and Chrysler are on the government dole – and that’s a strong leverage to use on the U.S. car companies.

What’s the next step?

The plan will be formally proposed in the Federal Register of pending rules and regulations. After that, it will be subjected to procedural hurdles at the Environmental Protection Agency and Transportation Department.

Material from The Associated Press was used in this report.