On a map, it looks like a quick, easy route from Prior Lake to Rosemount.

Wrong. County Road 42 is one traffic headache after another, and it's unlikely to get much better any time soon.

A recent Scott County study based on 2030 projections found that even with an expansion of the road to six lanes, average speed would slow and intersection congestion would increase. Of course, without the extra lanes, it looks even worse.

The road, long a source of traffic consternation, is the only continuous east-west arterial across northern Scott and central Dakota counties. Between now and 2030, more than 10,000 additional vehicles will travel it on an average day. And with stretches of commercial development, it's the scene of a battle between mobility and business access, with some drivers making long trips and others making a quick run to the convenience store.

This week Scott County commissioners and Prior Lake and Savage council members will all consider adopting the study, which encourages an eventual expansion to six lanes through the county.

Transportation planners are quick to note that the study is a tool for guiding future development, not a plan for immediate projects. But even as a vision, the study doesn't offer a lot of relief.

"We have numbers for what happens if they did six lanes, and there's not a lot of change -- that surprised me," Savage Mayor Janet Williams said. "I guess I thought another lane would whiz everyone through. So we need to think about the cost."

The only planned County Road 42 improvement in Scott County's 10-year plan, a 1-mile expansion to six lanes around the intersection of Hwy. 13, carries a projected cost of $17 million when it gets underway in 2017.

If the entire stretch from County Road 21 east through Scott County were expanded to six lanes, a move that would require acquisition of right of way in some areas, rush-hour speeds along the corridor in 2030 still would dip about 3 or 4 miles per hour during peak travel times. Without anything beyond currently planned improvements, speeds that hover around 30 miles per hour on the eastern side of the county would drop below 20 miles per hour by 2030.

The Dakota County chunk of the corridor isn't smooth sailing, either, despite a recent project to improve traffic flow.

A section of County Road 42 between Glendale Road in Savage and Irving Avenue in Burnsville is being upgraded to six lanes with more controlled access. It was a necessary improvement that has helped curb congestion in the area, but finding the political will and funding for that project wasn't easy, said Dakota County Commissioner Mike Turner.

Business owners, in particular, were hesitant to support it, fearing customers would speed by instead of stopping if a business didn't have a driveway on County Road 42. But Turner, who avoids County 42 even though he can practically see it from his Burnsville home, thinks of it differently: "People were afraid to stop in the businesses because they thought they couldn't get [back onto] the road in a timely fashion."

Katie Humphrey • 952-882-9056