Planners hope the race, which will use city streets for its 2.4-mile course, will only be mildly disruptive to traffic norms. But they make no guarantees.

"We don't really know" how traffic will flow, said Capt. Tom Conlin, who heads the traffic division for the Metropolitan Police Department. "It's the first time we've done this event."

Though other cities have held races on downtown streets, those races have been in business districts that are usually quiet on weekends. That's not the case here, where the city's center is a casino district that's teeming with visitors.

"We're different. We're 24-7. That's a unique challenge for us," Conlin said. "Overall, there's been a lot of thought put into the running of this. I think it'll go better than what some people think."

Still, motorists are being warned to stay away from downtown and the vicinity of the Interstate 15-U.S. Highway 95 "Spaghetti Bowl" interchange this weekend, if possible.

And those going to the race should plan to arrive early and leave late, taking into account the congestion around parts of Main Street, Bonneville Avenue, Grand Central Parkway and Ogden Avenue, among other streets.

"Clearly, the closer you get to the venue, the more delays you can expect," Conlin said. "If you don't have an urgent need to be downtown, I wouldn't go downtown for any other reason than to watch the race."

The racing festival is expected to draw around 150,000 people over its three-day run, with street closures building up through this week. The brunt of street closures are expected to take effect no later than 9 p.m. tonight.

Closed as of tonight are Main from Bonneville to Ogden; Bonneville/Alta Drive from Main to Martin Luther King Boulevard; Grand Central Parkway from Bonneville to Main; Fourth Street from Carson Avenue to Ogden; Casino Center Boulevard from Bridger Avenue through Ogden; and Carson and Ogden from Main to Fourth.

Already closed since Monday are Bridger between Main and Third Street; First Street from Bridger through Ogden; and Third Street from Carson to Ogden.

The temporary race track course itself follows a path along Main between Bonneville and Carson; Grand Central from Ogden to Bonneville; Bonneville from Grand Central to Main; Carson from Main to First and from Casino Center to Fourth Street; First and Casino Center between Carson and Bridger; Bridger between First and Casino Center; Fourth from Carson to Ogden; and Ogden from Fourth to Grand Central.

Those streets will be closed from 6 a.m. to 6 p.m., Friday through Sunday for the race and qualifying rounds. During that time, vehicular access to hotels, casinos and restaurants inside the track's perimeter will be entirely cut off.

From 6 p.m. to 6 a.m. Friday through Sunday, those streets will be reopened to traffic, but access will be only allowed through a series of gates set up amid concrete-and-steel retaining walls now ringing the course.

Those gates are at Main and Bonneville; Bridger and Casino Center; Carson and Casino Center; Ogden and First; and Ogden and Casino Center.

When those gates are closed, pedestrians will still be able to get in and out of the race area via pedestrian footbridges that have been set up at Third and Carson; Fourth and Fremont Street; Third and Ogden; and at Grand Central just south of the main grandstands.

The Fremont Street Experience and hotel/casinos inside the blocked-off area, which include the Plaza, Las Vegas Club, Binion's, Fremont, Fitzgeralds, Four Queens, Golden Nugget and Golden Gate, among others, will only be accessible by car during times those gates are open, though walkers using the footbridges will be able to get in and out at all times.

"We are open for business," said Sylke Neal-Finnegan, a spokeswoman for the Golden Nugget. She said guests have been warned in advance by e-mail or letter to expect the race and related traffic disruptions.

To accommodate guests during times streets are closed, the Golden Nugget will set up a satellite check-in tent at Third and Carson, from which guests can leave their luggage and walk to the hotel via the bridges, according to Neal-Finnegan.

And the hotel will have extra staff to help direct guests around the closures.

Guests staying elsewhere downtown can check with their hotels for any special check-in or access information.

"We're really not sure" if the race is a good thing for the hotel, Neal-Finnegan said. "We'll find out after the race ends what kind of impact it had. It's hard to say right now if it's a positive or negative impact."

But overall, "it's a great thing for downtown," she said.

Major downtown byways that will remain open and are suggested as detours include I-15, U.S. 95, Las Vegas Boulevard, Charleston Boulevard, Stewart Avenue, Bonanza Road, Washington Avenue, Eastern Avenue and Rancho Drive.

Satellite parking lots are being set up at Cashman Field and at a dirt lot at Martin Luther King and Alta. There will be free shuttle buses running between those lots and other downtown locales.

The Cashman shuttle will run Friday through Sunday from 5:30 a.m. to 3 a.m. with stops at Fremont and Las Vegas Boulevard; Third and Bridger; and Main and Bonneville.

The King/Alta shuttle will run Friday through Sunday from 6 a.m. to 8 p.m. to the World Market Center, adjacent to the race's grandstands. Officials expect parking there to be limited and to fill up quickly, compared to Cashman.

Taxi pickup and dropoff locations are being set up at Third and Carson; Fremont and Las Vegas Boulevard; and on Discovery Drive at the World Market Center.

Also, riders of Citizens Area Transit routes 105, 106, 108, 207 and "The Deuce" can expect many Grand Central, Main and Bonneville stops downtown to be discontinued through at least Sunday.

The only facility that will be closed due to the race is the Greyhound bus depot at Main and Bridger. From Thursday through Sunday, intercity bus service will arrive and depart from Citizens Area Transit Downtown Transportation Center on Stewart at Casino Center.