It’s just over one mile from the Mercer freeway ramps to Key Arena. But if you want to see the Storm play there this weekend, your choices for getting there are limited to looping past the southern shore of Lake Union on Valley St., contending with traffic headed for Fremont, or inching along through the series of ill-timed traffic lights along Denny Way. But relief is in sight, thanks to the controversial Mercer St. project, whose first shovel of dirt was turned today.Standing on either side of Congressman Jim McDermott, Mayor Mike McGinn and Governor Christine Gregoire temporarily put aside their differences on local transportation projects, smiled, and plunged shovels into a mound of dirt at the intersection of Mercer and Westlake. It marks the beginning of more than two years of construction through what was once storefronts along Mercer’s northern edge to create westbound lanes on the road straight off of I-5 for a cool $164 million.By the 2012 WNBA playoffs, the Seattle Department of Transportation hopes to have widened Mercer by 80 feet (pdf), adding three westbound lanes to the road taking cars on a more direct path to the Seattle Center, explains spokesperson Rick Sheridan.The high price tag, paid by various local, state and federal contributions (Sen. Patty Murray and U.S. Transportation Secretary Ray LaHood scooped up a shovelful of dirt today as well), comes in part thanks to the city needing to buy up the land along Mercer’s northern edge. SDOT has already leveled the West Marine store and Shell gas station that once sat there.In addition to turning Mercer into a two-way street, the city plans to eventually turn Valley, where cars now loop on their way to the Key, into a smaller street with wide bike paths so cyclists can avoid Mercer altogether. For now the plan stops at Dexter. Widening Mercer beyond there, all the way through to Seattle Center will require at least another $100 million, according to SDOT. Plus it will depend in part on the final design for the Alaska Way Viaduct replacement.But no one talked about that at today’s groundbreaking–not with McGinn and Gregoire holding those heavy shovels in such close proximity to each other.