The northbound onramp at the East Washington Street highway interchange — a long awaited, key component of traffic relief at the chronically congested area — is nearing completion, according to transportation officials.

The new onramp is part of a $23 million overhaul of the East Washington Street interchange, and could be completed and open to drivers as soon as this fall or as late as mid-2014, depending on weather, officials said. It will replace the existing onramp on the south side of East Washington Street, which requires northbound drivers coming from McDowell Boulevard to make a left-hand turn to access the freeway, creating a huge traffic backups.

The new onramp will be on the northern side of East Washington Street behind Raley's. The onramp bridge has been completed, as well as the embankment, but the ramp itself still has to be paved, according to Allyn Amsk, spokesman for Caltrans.

Additional work on the interchange project includes realignment of the on- and off-ramps on the south side of the East Washington Street. Amsk said that the entire project is projected to be completed by September 2014, but called that date a "conservative" estimate.

Ongoing construction will require occasional nighttime closures, said James Cameron, spokesman for the Sonoma County Transportation Authority, which coordinates with Caltrans on local highway projects.

As that project, which began in December 2011, begins to wind down, another city project, to replace an aging water pipeline is beginning on East Washington Street and will run from Edith Street to the bridge over the Petaluma river, promising to bring more congestion to that stretch of road.

But while some lane closures and delays will continue, the worst may be over for East Washington Street drivers, who have been beset by traffic woes for more than a year.

The peak of road construction began last summer, when the city was replacing a section of water main running from Highway 101 to Edith Street, Caltrans was working simultaneously on the East Washington Street Highway 101 interchange and construction was in full swing at the newly opened East Washington Place shopping center, creating multiple road closures and slow-downs along the already congested street. Compounding that was railroad crossing work making way for the SMART commuter train.

"It was a mess, we know that," acknowledged Public Works Director Dan St. John. But now, he said, SMART has completed its work, the East Washington Place shopping center is open, much of the most intrusive work has been finished on the East Washington Street interchange, and traffic signals have been re-timed.

"We're hoping the community won't see anywhere near the impacts they saw last summer," St. John said.

Still, there will be impacts from now until November as the city replaces the large, aging lines that carry water across town and are more than 85 years old in some cases. It's the third and final phase of an effort to replace the aging pipe running down East Washington Street that began four years ago.

Businesses on the road have expressed concern about the effect of the water main project on their bottom line. Hearing these concerns, the city held a meeting with the businesses on Aug. 12.

St. John said the water main work is necessary to prevent future disasters that could be caused by the old water main breaking, as it did five years ago, creating a crater in the road and causing the pavement to lift. Still, St. John recognized the hardship on businesses and said the goal is for the work to be completed before Thanksgiving, when the holiday shopping season begins. If the work is not done by then, St. John said the city could also delay the project until the spring. After hearing from business owners, the city also agreed to have its contractor start work earlier in the day so that it could be finished before peak afternoon traffic.

St. John said he knew drivers were frustrated with the traffic, but asked them to be careful on the road while construction continues. "The workers are out there, they've got a tough job with traffic whizzing by, and I can't say enough to slow down and be careful," he said.

Police Traffic Sgt. Ken Savano added that officers will be patrolling the construction zone on East Washington Street to ensure that drivers are paying attention and being safe.