MILL CREEK — A bit of road relief has arrived for the fastest-growing part of Snohomish County.

There’s years of work still to come.

A ribbon-cutting ceremony on Tuesday marked the first phase of improvements to 35th Avenue SE. Crews widened the formerly two-lane stretch by adding a continuous center turn lane from Seattle Hill Road south to 180th Street SE. There are bike lanes, as well as curbs and sidewalks, on both sides of the north-south arterial. The work spanned about 1.8 miles and started last year.

“As you have probably figured out, there’s tremendous population growth in this area,” said County Council Chairman Terry Ryan, whose district covers the surrounding neighborhoods.

On Tuesday afternoon, Ryan joined other dignitaries at Tambark Creek Park to celebrate the milestone.

Ryan said fixing the road network in his district, which includes the Mill Creek and Bothell areas, was a priority after he was elected to the county job in 2013. Before that, he was a long-time member of the Mill Creek City Council. Early plans called for widening 35th to five lanes, but by the time he arrived at the county, it was too late for that.

Instead, public works staff focused on the upgrades that were showcased this week.

“If we had not done that, all the development on 35th Avenue would have had to be shut down because the traffic was so bad,” Ryan said.

The recently completed work cost about $14 million, including construction, property acquisition and design.

It’s part of a combined $81 million of ongoing road projects in the area between the Bothell-Everett Highway and Highway 9. Several other projects are planned within the next four years or so.

“We’re making steady progress, we’re chipping away at it,” County Executive Dave Somers said.

A second phase of construction along 35th Avenue could start as early as next year. That will extend the same kinds of upgrades south from 180th Street SE to Maltby Road, which also is known as Highway 524. That section of 35th passes by North Creek High School, and the upgrades should make walking or biking to school safer.

Soon after that, the county hopes to start work to punch through a new north-south arterial along 43rd Avenue SE and Sunset Road.

That’s not all.

Public works officials hope to start widening 180th Street SE next year. That project would expand the road to five lanes, from three now, between Bothell-Everett Highway and 23rd Avenue SE. A second phase would extend those improvements east to 35th Avenue.

Improvements are under construction now along Grannis Road and 196th Street SE. Those roads are a partially diagonal, east-west connection between 35th Avenue and Bothell-Everett Highway.

Last summer, county crews finished improvements to Seattle Hill Road. Mill Creek in March saw through a major project to fix a sinking stretch of 35th Avenue farther to the north.

Population growth is sure to continue putting a squeeze on the road network, especially in southwest Snohomish County.

Regional growth projections anticipate that the county will add about 250,000 more people over the next 20 years, Somers said. More than 800,000 people live here now.

Noah Haglund: 425-339-3465; nhaglund@heraldnet.com. Twitter: @NWhaglund.