The sky is not falling, the stock market has not crashed and the country is not being invaded.

But, if you use I-15 to access downtown Salt Lake City, Labor Day weekend is the beginning of the end - the end of your current driving practices, that is.Wasatch Constructors and the Utah Department of Transportation on Thursday announced a series of ramp closures and openings that will change the way people drive to and from Salt Lake City.

It's all part of the ongoing $1.59 billion I-15 reconstruction project. With 16 months down and 35 more to go, the massive effort has progressed to the point where the reconstruction of one major downtown interchange - 600 North - is nearly complete. And the destruction of another - 600 South/500 South - is about to begin.

Six separate changes, or groups of changes, are planned for the downtown segment of the 17-mile reconstruction corridor between Sept. 4 and June 15 of next year. Four of the six will occur by the middle of October.

The end results of the most immediate changes are as follows:

- By Labor Day, drivers coming from the south will have to exit I-15 at 900 South, 600 North or 1300 South. The northbound I-15 off-ramp at 600 South closes Sept. 5.

- By early October, southbounders motoring in from Davis County and beyond will be able to use the new 600 North interchange to enter downtown. If they miss that exit, however, it will be another five miles - at the I-80 junction - before they can get off the freeway.

- The trip home will change, too. Beginning Sept. 19, northbounders will follow 400 West to 600 North. Southbounders, meanwhile, will be able to take the 500 South onramp to I-15 until Feb. 1 of next year. After that, they will have only the 900 South and 600 North entrances to choose from.

"One of the things we've been really sensitive to is the inbound program. We really want people to find downtown," Gary Adams, Wasatch Constructors' maintenance of traffic engineer, said during a press conference at the contractor's headquarters on the city's west side.

"As you look at the inbound program, it's really quite simple. There really is very little difference, and we really don't expect there to be any problem with this."

Here is the schedule for downtown ramp closures and openings announced Thursday:

1998

Sept. 4-5 - The northbound I-15 offramp at 600 North will open Sept. 4, followed the next day by the closure of the northbound I-15 offramp at 600 South, which will re-open a year later.

Sept. 18-19 - The 600 North onramp to northbound I-15 will open Sept. 18, followed the next day by the closure of the 500 South onramp to northbound I-15. That ramp will not reopen. It will be replaced by the new 400 South interchange, to be open for northbound entry by June 15, 1999.

Oct. 2-5 - On Oct. 2, the 600 North viaduct will open to east-west traffic above I-15 and the southbound I-15 offramp at 600 North will open. On Oct. 5, the southbound I-15 offramp at 600 South will close. That ramp will not reopen. It will be replaced by the new 400 South interchange.

Oct. 16 - The 600 North on-ramp to southbound I-15 will open.

1999

Feb. 1 - The 500 South onramp to southbound I-15 will close. It will reopen July 1, 2000.

June 15 - The 400 South on-ramps to both southbound and northbound I-15 will open to all traffic. When the project is finished in July 2001, however, the southbound ramps will be restricted to use only by high-occupancy vehicles.

Best options

Although northbounders entering the city still will have three viable options after Labor Day, Wasatch is promoting the 900 South offramp as the best choice and 600 North as the next-best ramp.

"Right now, 900 South is carrying only about one-third of the traffic it can accommodate," Adams said, adding that all of that capacity likely will be used during peak hours when the inbound detour is in effect.

Adams said Wasatch still is working with Salt Lake City to finalize the agreement to use 400 West as the primary route for motorists to move between the 600 North interchange and downtown. Traffic on 300 West is already at capacity during rush hours, he said.

The contractor hopes the city will allow it to place a barricade on 600 North just west of 300 West so that freeway traffic will have no choice but to use 400 West as the primary downtown access route.

Wasatch also is considering a temporary southbound offramp at one of four potential downtown locations to provide an additional exit between 600 North and I-80. But if such a ramp is created, it probably won't open until next fall. The southbound I-15 offramp at 400 South, meanwhile, will not open until the fall of 2000.

For more information, check the contractor's Web site at (www.I-15.com).