BANGOR – As part of its effort to build a new $23.6 million Supercenter here, Wal-Mart will be required to make an estimated $3 million in improvements to Stillwater Avenue.

But the work – which will be a requirement of the traffic movement permit the megaretailer expects to receive soon from the Maine Department of Environmental Protection – must be completed before the 209,000-square-foot store opens its doors for business.

That is because city officials and residents alike want to avoid the kind of gridlock experienced after the Bangor Parkade shopping center opened in fall 2005, before transportation improvements could be completed and tested.

The traffic signal at Parkade, also on Stillwater Avenue, underwent some adjustments as recently as last month and was reportedly functioning well as the city headed into the busy post-Thanksgiving shopping season, according to Mike Waugh, a traffic engineer associated with both projects.

Slated to open in spring 2008, the Wal-Mart Supercenter would replace an existing 114,000-square-foot store less than a mile away on Springer Drive.

The Supercenter, slated to be built on a 50-acre site off Stillwater Avenue behind the Blue Seal Feeds store, would be reached by an access road adjacent to Crossroads Mall. Plans currently call for parking for 700 vehicles, with a bus stop at the store’s entrance.

With the Supercenter projected to bring about 550 vehicles an hour to the busy Bangor Mall area during its weekly traffic peak on early Saturday afternoons, owners of other commercial developments in the project area, including the Crossroads Mall, are worried that access to their stores will be cut off if traffic backs up.

To that end, Waugh and other representatives of Wal-Mart Real Estate Business Trust outlined plans to install a new signal-controlled access drive, widen Stillwater Avenue from two to five lanes and widen portions of Hogan Road near Stillwater Avenue to provide additional turning and storage lanes.

In addition, the developer plans to interconnect and coordinate all traffic signals in the affected area to obtain a level of service of D or better, a rating that is acceptable to transportation regulators.

Like school report cards, the rating system runs from A through F, with A representing the shortest delay and F the longest, city Planning Officer David Gould noted during a planning board meeting last week at City Hall.

In his background memorandum to planning board members, Gould wrote that City Engineer Jim Ring is closely involved with the planning process.

“Although the MDOT traffic permit has yet to be finalized, the proposed public improvements and mitigation measures appear to sufficiently mitigate impacts from this development, meaning safety, congestion, and capacity would be no worse than present condition,” Gould wrote.

The planning board’s votes last week to grant site development plan approval for the overall project and conditional use approval for a proposed garden center followed a marathon meeting.

While environmental concerns were raised, traffic concerns dominated the discussion.

As proposed, the main access to the Supercenter will be from Stillwater Avenue. That was not, however, the top choice for city officials and the owners of commercial property near the Wal-Mart site, who had hoped to find a way to compel Wal-Mart to build an extension to Hogan Road to serve the Supercenter.

A sticking point is that the land needed for the right-of-way is privately held.

Representatives of the Eremita and Valley families, who own the Crossroads Mall, said the families are willing to donate their portion of the right-of-way to the city.

Wal-Mart representatives, however, have not yet been able to negotiate a deal with the owners of the Country Inn, who hold the remaining portion.

Wal-Mart’s initial plan, presented in July, called for a nearly 218,000-square-foot Supercenter to be located on a 50.6-acre site on Stillwater Avenue behind Blue Seal Feeds.

The project was scaled back to 209,000 square feet, largely because planners scrapped a tire and lube center, a feature that already exists at the corporation’s Sam’s Club store on nearby Haskell Drive.

In addition, the parking lot was scaled back by about half an acre.