If you've had it up to your dashboard with freeway closures, Wasatch Constructors has some good news for you.

The first major interchange to be completely rebuilt as part of the $1.59 billion I-15 reconstruction effort will open this weekend.And if driving on that new, sparkling white, concrete pavement doesn't thrill you, how about this: The massive project is now $7 million under budget and likely to stay that way.

Wasatch, the I-15 contractor, plans to reopen the remaining three ramps of the 600 North interchange - and the 600 North viaduct above I-15 - about 4 p.m. Saturday. The northbound I-15 offramp at 600 North opened in September.

It took more than 17 months for Wasatch to demolish the old interchange and build a new one. That's about five months longer than expected, partly because its boss, the Utah Department of Transportation, decided this summer that the 600 North ramps should be paved in concrete like the rest of the new freeway instead of asphalt.

"Concrete costs a little more up front but has much lower maintenance requirements than asphalt," Wasatch spokesman Brian Mauld-win said of the new I-15 pavement, which is expected to last 50 years before needing replacement.

"If there's less maintenance, then you'd have fewer closures (in the future), which is good news for drivers."

The white color of the concrete, known commercially as Portland Cement Concrete, comes from the curing compound that is applied after it is poured.

South Salt Lake Valley motorists will get a closer look at the new concrete pavement beginning Nov. 9. That's when Wasatch now plans to have southbound I-15 traffic switched onto the new southbound side of the freeway between I-215 and 9000 South.

By Nov. 16, northbound I-15 traffic also will be moved onto the new white concrete on the southbound side, from I-15 to 9000 South. Crews will need to close a 60-block section of the freeway for 35 hours both weekends to accomplish the switchovers.

With this weekend's opening of the southbound I-15 offramp at 600 North, crews will be free to close the southbound offramp at 600 South. That is expected to happen about 3 a.m. Monday.

Commuters heading into Salt Lake City on southbound I-15 Monday morning can exit the freeway at 600 North. An extra left-turn lane has been added to the intersection of 400 West and 200 South to improve traffic flow into the downtown area from 600 North.

The openings, closings and detour routes are of primary interest to motorists. But state lawmakers are more concerned with the financial bottom line of the I-15 rebuild. They, too, received some good news this week.

UDOT and Wasatch officials told the Legislature's Transportation Interim Committee Wednesday that they saved $7 million in the first 18 months of the 51-month project, primarily by making changes to designs for the new 500 South onramp and 2100 South interchange. Some money also has been saved because UDOT is now in charge of maintaining the existing freeway instead of Wasatch.

UDOT Deputy Director Clint Topham said that $7 million in savings could evaporate if an unexpected change in I-15 work is necessary. But he is "cautiously optimistic" that won't happen since most of the design work associated with the 17-mile rebuild is complete.

If the savings hold, Wasatch's $1.325 billion contract will end up as a $1.318 billion contract. Put in that context, $7 million doesn't look like a whole lot. It represents less than a half percent of the total project budget.

But to some lawmakers, any savings in state government is big - and very good - news.

"We're very determined to not have to come back to you for money," UDOT Executive Director Tom Warne told the committee.

Warne said the I-15 budget is now even slightly below that $1.318 billion contract figure. As of the end of September, UDOT had paid Wasatch $600.9 million of that adjusted contract amount.

UDOT officials reviewed with the committee how the department is streamlining every facet of its operations in an effort to transfer additional costs savings into the I-15 project.

UDOT has scheduled a ribbon-cutting for 10:30 a.m. Saturday to celebrate the opening of the 600 North interchange.