Fort Worth, Texas ? Bruton Smith built it, and they’re still coming.

More than 300,000 NASCAR fans will descend this weekend on the 5-year-old Texas Motor Speedway, a monstrous track big enough to swallow eight Texas Stadiums. They’ll spend $50 million or so on tickets, luxury suites, camping spots, concessions, souvenirs and the like.

A big, modern facility in a major urban market, TMS exemplifies stock-car racing’s transition during the last decade from its regional, rural roots into a big-time, mainstream sport. But the industry won’t create anything like it anytime soon.

“I don’t think you’re going to see a facility on this grand scale built in the near future,” said Eddie Gossage, the speedway’s general manager.

Smith, chairman of North Carolina-based Speedway Motorsports Inc., put Dallas-Fort Worth on the racing map by investing $250 million to build and improve TMS, the site of Saturday’s O’Reilly 300 Busch series race and today’s Samsung/RadioShack 500 Winston Cup event.

The Fort Worth speedway was part of a track building boom over the last seven years. As NASCAR’s popularity soared, facilities popped up in new markets: the Miami area in 1995, Las Vegas in 1996, near Los Angeles and St. Louis in 1997, outside Cincinnati in 2000 and near Chicago and Kansas City in 2001.

Winston Cup races, which draw free-spending crowds of up to 250,000, are the cash cows of the racetrack business. The schedule expanded from 29 events in 1992 to 36 this year, a number that’s unlikely to increase much further because of holidays and the sport’s two-month off-season.

TMS and other new tracks are vying for second Winston Cup races, so there aren’t enough dates for existing tracks, let alone new ones.

A new track could host other racing series  the Indy Racing League, the Busch series or NASCAR’s truck division  but those bring smaller crowds. TMS, for example, draws about 70,000 fans for an IRL race, among the best turnouts on the circuit.

“Building new tracks costs $100 million and more  sometimes a lot more  and you can’t put up that kind of money for an IRL or Busch race,” said Joseph Hovorka, who tracks the industry for Raymond James & Associates. “You have to have a Winston Cup race to make something that big profitable.”

Smith’s Speedway Motorsports, which operates six tracks, isn’t about to make a big-money bet on building a new facility.

“Speedway Motorsports is not actively researching or looking for sites to build additional speedways at this time,” said Lauri Wilks, the company’s general counsel.

NASCAR continues to thrive in the second year of its $2.4 billion national television deal. Adding tracks such as TMS  big facilities in big markets  would expand live crowds and television audiences.

The money might force NASCAR to move a few races from older facilities to modern ones, but the calendar simply won’t allow enough events to spur new building.