Many Pittsburghers don't realize it, but 35 miles of the Mon-Fayette Expressway are open and serving highway travelers. Now comes the hard part.

The long-envisioned interstate through the Mon Valley, with an ultimate connection between Pittsburgh and West Virginia, is heading into its trickiest phase yet: the $2 billion, 24-mile forked terminus in Allegheny County. Forging into a zone with denser population, a greater number of established communities and a more complicated transportation grid, the Turnpike Commission will face many more questions and challenges in this segment of the construction.

Now is the time for community advocates to speak up about how they feel the highway should fit in with the local terrain.

Various interests representing Pittsburgh's Oakland section, for instance, are concerned about how the expressway will touch down at Bates Street, a major access point to a busy neighborhood that is home to universities, hospitals and cultural centers. As a winding, outmoded two-lane connector between South Oakland and the Parkway East and Second Avenue, Bates is already overrun by vehicles at peak hours. The trick in linking it to the expressway will be how to do it in a way that eases, not constricts, traffic flow.

Fortunately, Joe Brimmeier, executive director of the turnpike, has promised that the Allegheny Conference's Oakland Investment Committee and Oakland Task Force will have much input to the final design of the Bates interchange. That doesn't mean it will be easy or that all will go smoothly, but it is the latest public signal by the turnpike that it wants the highway to be an asset to each community it serves. Pittsburgh needs to hold the agency to it.

A consultant hired by local foundations to study the expressway's impact on Oakland turned in higher numbers on traffic and congestion than the turnpike's data. That's just one point of disagreement that must serve the basis for future discussions.

To the turnpike's credit, other design advisory teams to seek local input will be set up for critical points along the route: Dravosburg, Turtle Creek, the Braddock area, Nine Mile Run and the Glenwood-Hazelwood corridor. Local citizens with ideas on how to mitigate the expressway's negatives and enhance its positives should take the turnpike up on its offer.

Given the expense and impact of such a project, no public agency should be allowed to behave as if "it's my way or the highway."