ARLINGTON — The busy stretch of Highway 531 near the city’s airport and industrial park is set to get an update local leaders and business owners have been seeking for 20 years.

That’s thanks to $39.3 million being included in this year’s state transportation package, signed by the governor this week. The money will pay to widen a mile-and-a-half segment of Highway 531, also known as 172nd Street Northeast.

The road branches off Highway 9 and cuts through Smokey Point, connecting the Arlington Airport, industrial park, commercial centers and residential neighborhoods to each other and to I-5. The area grew up quickly over the past two decades, adding new businesses with hundreds of employees and new shopping centers with steady streams of customers. The size of the road, though, didn’t keep pace.

“It’s the key corridor that carries people from our industrial businesses behind the airport to I-5,” Arlington Mayor Barbara Tolbert said.

The road narrows to two lanes at 43rd Avenue Northeast, just as it reaches the city’s industrial heart. There’s no middle turn lane, no sidewalks and minimal shoulder space, Tolbert said. That makes the route dangerous and can slow traffic to a crawl during peak commuting hours.

Between 17,000 and 23,000 cars use that part of the highway each day, according to the state Department of Transportation’s 2014 traffic report. About 22,000 cars pass the highway’s intersection with 43rd Avenue, and the state expects that number rise to 26,000 by 2020 and 36,000 by 2040.

The road also has seen up to 40 crashes per year in the past, and one accident can back up traffic for hours because there is no extra lane or shoulder space, according to the city.

Mike Kooy runs dispatch for his family’s business, John H. Kooy Trucking, Inc. The 35-year-old company moved from Mukilteo to Arlington about 10 years ago and is located on 67th Avenue Northeast, which connects to Highway 531.

Kooy has seen a lot of rear-end accidents on the highway and said that, during heavy traffic, drivers can sit at the same light for five cycles before they get through. Widening the highway is a necessity, he said.

“For us, it’s two things,” Kooy said. “One of them is safety and the other is timing. It’ll take away the major bottleneck.”

The project will widen Highway 531 from two lanes to four lanes, and include a median. Preliminary designs call for roundabouts to replace the stoplights at 43rd, 51st, 59th and 67th avenues. Left turns would be blocked except at intersections.

“Roundabouts have been selected because of mobility,” Arlington Public Works Director James Kelly said in an email. “They are safer and they take up less right-of-way.”

The state spending plan would start directing money toward the project in 2019, with the bulk of the work between 2021 and 2025.

“I know a lot of people would like it to start tomorrow, but we’re farther than we’ve ever been before,” Tolbert said. “It’s fully funded and almost fully designed.”

Previous plans for the highway called for extensive rebuilding and roadwork costing more than $50 million. City and state Department of Transportation officials studied the highway and sketched plans in the early 2000s and again around 2010. At the time, the price tag was too high.

The city worked with the Department of Transportation for about eight months to whittle the original design into something more affordable, Kelly said. The Federal Aviation Administration now is reviewing the plans because part of the highway passes through the Arlington Airport’s runway protection zone.

Kari Bray: 425-339-3439; kbray@heraldnet.com.