ALBANY — The state is advertising for consultants to conduct an eagerly awaited new study of traffic conditions on Route 17 and recommend potential solutions for alleviating congestion on the four-lane gateway to Orange and Sullivan counties.

Prospective consultants have until Wednesday to respond to the Department of Transportation’s request for expressions of interest. The DOT anticipates having a consultant in place by Oct. 1 for what will be an 18-month study. The completion date is March 31, 2021.

The DOT’s small step forward on the study got a rousing cheer from leaders of the 17 Forward 86 Coalition who are campaigning for the construction of a third lane in both directions on Route 17.

“This is great news for this critical project,’’ said Maureen Halahan, president and CEO of the Orange County Partnership and co-chair of the coalition, in a statement.

Marc Baez, her co-chair and counterpart at the Sullivan County Partnership, described the study as laying the groundwork for making the third lane a reality and securing funds for its construction in the DOT’s next capital plan.

The coalition was instrumental in getting state legislators to include up to $5 million in the 2018-19 budget to pay for the study.

The DOT said the consultant will be charged with defining the transportation issues in the Route 17 corridor and then developing and evaluating solutions. Public meetings will be held to gather suggestions.

At the same time, the consultant will project future traffic conditions, assess design alternatives, analyze engineering considerations and evaluate potential impacts.

The study, to a certain extent, will build on one that the DOT conducted in 2013. The so-called Route 17 capacity study found that traffic volumes through 2045 would support construction of a third lane from the Thruway to Interstate 84 but no farther until or unless volumes changed.

Since then, Sullivan County has seen two major attractions, Resorts World Catskills and the nearby Kartrite Resort and Indoor Waterpark, open. Next year, Orange County will see Legoland New York open and, in two years, a possible expansion of Woodbury Common Premium Outlets.

This time around, the DOT will have the benefit of new federal rules that allow agencies to use the data collected in these kinds of studies in future environmental reviews for specific projects.

The Federal Highway Administration and the U.S. Environmental Protection Agency adopted the new rules in recognition that the work is often duplicative and only serves to delay projects.