Consumers should have an easier time comparing the fuel economy of cars and light trucks once new consumer labels unveiled today go into effect.

U.S. Transportation Secretary Ray LaHood and Environmental Protection Agency Administrator Lisa P. Jackson unveiled the new set of labels this morning at a live press conference hosted on the Web.

Prior to this, car labels hadn't been updated for 30 years.

Each new label differs slightly depending on the car's drive train or fuel source. (Click for a PDF of all labels.) Labels in the set include those for gas, flex-fuel gas-ethanol blends, compressed natural gas, diesel, hydrogen fuel cell, electric, hybrids, and plug-in hybrids.

All labels supply the usual combined city/highway mileage average as well city and highway mileage separately. But now the label also includes the number of gallons burned per 100 miles. It gives an estimated annual fuel cost for the car, and indicates how that compares to the cost of fueling an average car in that class. It tells you the average miles per gallon range for cars in that class, as well as the best MPG achieved by a car in that class.

For alternative-fuel vehicles, an MPGe (miles per gallon equivalent) rating is used for comparison to traditional vehicles. Labels for electric vehicles also include how many miles it can get on a single charge, as well as how long it takes to charge the car's battery.

Perhaps the coolest feature of the new labels is that they include QR codes. With their smartphone, consumers can scan the code on the label that works with FuelEconomy.gov and use it to compare other cars. The app used in conjunction with the QR code gives consumers access to more information on the car in front of them, and allows them to see how the car would operate based on their own personal driving habits and local information they enter in the app. (Click to see a how-to video.)

But not everyone is happy about the new label.

One of the original prototypes included a letter grade system of A+ to D for a car's fuel economy and environmental impact. The system would have given small cars with good gas mileage A's and B's, while SUVs and pick-up trucks would have likely gotten C's and D's. The letter grade system was publicly backed by several consumer and citizen advocate organizations, among them the Natural Resources Defense Council, Sierra Club, and Union of Concerned Scientists. The official label unveiled today doesn't include that letter grade system.

Instead it includes a rating for "Fuel Economy and Greenhouse Gas Rating" on a scale of 1 to 10, as well as a "Smog Rating (tailpipe only)" on a scale of 1 to 10, with 10 being the best in both instances.

It's been rumored that dealers and automakers were lobbying against the government putting a letter grade on cars, which is why both LaHood and Jackson were questioned on the letter grade being dropped by several reporters throughout the press conference

"Yeah, I know. You heard the dealers as well as manufacturers said they preferred not to have the letter grade. But, it really was about the consumer. It you're doing a label it's not for the manufacturer or dealers. What we found is that half the people didn't think a letter grade gave them enough information, and there was some confusion that the letter grade meant for the quality of the whole car," said Jackson.

"So we used the 10-point scale, as on other appliances and electronics products. And that's why fueleconomy.gov is going to be so important. Take that info of the vehicle you're looking at and plug in where you live, and your price at the pump right now. You can even get a sense of what the electricity emissions are for your area for an electric car," she said.

The label has the endorsement of Consumers Union, the nonprofit publisher of Consumer Reports. The group had originally expressed concern that the earlier version of the labels did not containing enough specific and distinguishable information for comparing mid-range cars.

"This is a lot better than the original labels that you had. That is the result of the fact that you listened and took input from those with consumer interest. This is right down our alley. You're provided easy, useful info for when it comes to fuel economy. We from Consumer Union and Consumer Reports applaud what you've done, and this will be very good for consumers," said Consumers Union President and CEO Jim Guest.

The new labels will be legally required to be displayed on all 2013 model cars and light trucks. But consumers could see them sooner if automakers decide to voluntarily adopt them for their 2012 models, according to Jackson.

LaHood said both agencies also plan to unveil a similar label for heavy-duty trucks in July.

Correction 12:50 p.m. PT: An earlier version of this story misstated the day the announcement was made. It was today.