Six road blocks that mark the end of the roadway at the South Lawrence Trafficway stand on Tuesday, July 10, 2012. The Kansas Department of Transportation is planning to go ahead with a six-mile, four-lane extension to Kansas Highway 10 next year.

In its ruling Tuesday that upheld plans for the South Lawrence Trafficway, a U.S. 10th Circuit Court of Appeals panel said any errors in a noise study were “harmless.”

The Kansas Department of Transportation cheered Tuesday’s ruling because officials believed it ended a legal challenge. KDOT hopes to begin construction in fall 2013 on the six-mile, four-lane leg of Kansas Highway 10 that will connect the highway east of Lawrence with the section on the west side of the city.

Opponents of the route had argued that the process KDOT and the Federal Highway Administration used to arrive at what is called the 32nd Street route, or 32B, was flawed. They also said the government’s analysis too quickly dismissed alternative routes — particularly under a law that protects historic sites, including property associated with Haskell Indian Nations University.

Under the current plan, a nearly $20 million mitigation plan would move both Haskell Avenue and Louisiana Street farther from the current Baker Wetlands and add about 260 acres of new wetlands to the area.

Project opponents asked federal and state officials to consider a route much farther south — along a 42nd Street alignment — because they said highway officials misrepresented the likely impact the road would have on the area and they don’t understand the cultural significance of the wetlands.

But the three-judge panel in the case, Carlos F. Lucero, Stephanie K. Seymour and Timothy M. Tymkovich, who wrote the decision, sided with state and federal highway officials on every issue.

A key part of the opponents’ argument was that a noise study on the project was not complete because it did not measure predicted noise levels of the new SLT against existing noise levels.

The judges said that the noise level comparison was only one step in the process and that the government acted correctly in the next phase when it identified “noise abatement measures,” including the addition of sound barriers in the project.

“Because any error at stage one did not actually prevent the government from proceeding to stage two, and because the analysis at stage two was conducted correctly, we see no possible harm,” Tymkovich wrote.

In other parts of the opinion the court found:

• The government “did not act arbitrarily or capriciously” in not including an alternative 42nd Street route, known as 42C, which the plaintiffs favored. Highway officials determined that corridor would have been more dangerous because of required curves.

• KDOT and FHWA were reasonable to use the effect of 23rd Street traffic levels to determine that the 32nd Street route would meet the project’s traffic-reduction goals better than a 42nd Street route.

• The FHWA provided sufficient justification to conclude that alternatives to the route it selected were not prudent, even when not considering the mitigation measures of the 32nd Street plans.

“Here, it is clear from the record,” Tymkovich wrote, “that the government took a ‘hard look’ at several relevant factors — project goals, cost, floodplain impacts, accelerated development, and environmental impacts — and reasonably demonstrated that (a 42nd Street route) posed enough problems along these factors to render that alternative imprudent.”