When it launches this spring, the 2010 Toyota Prius will break fuel economy records with a 50 miles-per-gallon rating, Toyota announced Monday.

Toyota has sold more than 1.2 million of the hybrids over the past 10 years, including 700,000 in the United States. The new model of the car will be quieter, roomier and equipped with more standard features, Toyota said.

But the main attraction for the car is its improved fuel economy.

The first-generation Prius, which was introduced in 1997 and rated at 41 EPA combined miles per gallon, was replaced by the current model, which is EPA rated at 46 miles per gallon, combined city/highway.

Using a combination of technologies, fuel efficiency was increased to an EPA estimated city/highway mpg rating of 50 in the city, 49 on the highway and a combined 50 mpg for the new Prius.

A larger and more powerful 1.8-liter engine combined with an electric motor will allow the 2010 Prius to generate a net horsepower of 134, an improvement of 24 horsepower over the previous generation.

Toyota said the larger engine will actually help improve highway mileage by creating more torque and allowing the new engine to run at a lower average rpm on the highway. Vehicles use less fuel when operating at lower rpm.

Pricing for the 2010 Prius will be announced shortly before it goes on sale in late spring.