HOUSTON - Thousands of race fans swarmed Friday to the U.S. city Houston's downtown to enjoy a three-day Grand Prix which features IndyCar Series races and several other series of auto races.

The Shell and Pennzoil Grand Prix of Houston got rumbling Friday at 10:30 a.m.CST, when IZOD IndyCar Series drivers took to the 2.7-km street track at Reliant Park for their first practice session, scheduled to run until noon, according to Houston Business Journal's website.

IndyCars are capable of speeds up to 368 kmph. Tops speeds of approximately 288 kmph are expected at Reliant Park.

The weekend's two IndyCar Series races, both of which will be nationally televised, are scheduled for Saturday and Sunday. Houston is one of three cities this season, along with Toronto and Detroit, to have been awarded a double-header.

With just one race left after Houston - next weekend in Fontana, California - three-time Indianapolis 500 champion Helio Castroneves, currently the points leader, could all but wrap up a championship with a strong showing in the Bayou City.

Another former Indy 500 champion, Houston-born racing legend A.J. Foyt - one of two drivers in history, along with Mario Andretti, to win both the Indy 500 and the Daytona 500 - will have have a major presence at Reliant Park.

While the IZOD IndyCar Series races are the weekend's headliners, there will be a bunch more going on at Reliant Park - including ten other races, representing six other series. Fans can enjoy the Festival of Speed including live music, food and merchandising vendors, and nonstop entertainment for the entire family in the Family Fun Zone.

The Shell and Pennzoil Grand Prix of Houston is an annual auto race on the IndyCar Series circuit. It was held in a street circuit located in downtown Houston for four years, then returned after a four year hiatus for two years on a course laid out in the parking lot of the Reliant Park complex. The last race was held on April 22, 2007.