Nine months ahead of schedule, starting Tuesday afternoon drivers will have a new way to get on and off Interstate 405 in downtown Renton.

They’ll drive the new onramp to northbound I-405 from Talbot Road and get off southbound I-405 on an offramp to Talbot. The Stage 2 I-405 widening project also includes a new lane in each direction on the freeway near City Hall.

For now, at least, the completion means that travelers will no longer face construction delays on I-405 through Renton for perhaps years to come.

The idea behind the new half-diamond interchange is to relieve the traffic load at intersection of I-405 and State Route 167/Rainier Avenue, which Lisa Hodgson, the Stage 2 project engineer, says is one of the most congested in the state.

The new ramps will serve the residential areas on Talbot and Benson hills, as well as the Fairwood area.

“It’s very exciting,” said Hodgson of the project that began in summer 2009. Along the way, the old Benson bridge was torn down and replaced with a new one and thousands of yards of soil moved to Renton Hill to make way for the onramp.

Stage 1 of the current round of 405 improvements included additional lanes from roughly Southcenter to SR 167. With the completion of Stage 2, no further construction project on 405 in the Renton area are currently funded with revenue from the state gas tax.

The next likely project is a massive one to improve the I-405/SR 167 interchange, which could include flyovers. That project is part of an extensive plan developed for projects along the 405 corridor from Southcenter to I-5 beyond Bothell and Woodinville.

The earlier Stage 2 completion date – the original date was September 2011 – was possible because the effort to move those thousands of yards of soil for the onramp went so smoothly.

The project cost nearly $84 million. Some work remains to be done, including some landscaping, painting and electrical work. That work should be completed in early spring.

“It’s coming together really well, other than the unpredictable weather,” said Hodgson. The snowstorm just before Thanksgiving threatened to derail the goal of opening the interchange by year’s end.

The state Department of Transportation is doing traffic counts now on Talbot Road as part of its effort to determine just how much traffic the new ramps will remove from the I-405/SR 167 interchange.

Those counts will continue for several months. Travel patterns during the holidays are “a little bit different” than during the rest of the year, Hodgson said. So, the state wants to count during a more normal time of year to determine the “split with 167,” she said.

The ribbon-cutting for the new ramps begins at 1:30 p.m. on Talbot Road, not far from Renton City Hall. Attending will be dignitaries, including local officials and Paula Hammond, the state transportation secretary.

Among those the first to use the offramp will be Renton resident Tami Green, who has watched the project closely.

The switch to the new lanes and ramps could take most of the afternoon. The new southbound lane will open first, then the offramp. The northbound lane will open next, followed by the onramp.