Continuing his efforts to alter the Highway 520 bridge replacement plan, Seattle Mayor Mike McGinn sent a letter to Microsoft CEO Steve Ballmer on Wednesday outlining his concerns about the bridge's design and offering to discuss the project at a town hall on the software giant's campus.

Addressing the letter to "Steve," McGinn told Ballmer: "The current 520 bridge is unsafe and its congestion is a serious regional problem. I believe the thousands of Microsoft employees who spend far too much time away from their families stalled on that bridge deserve better." He went on to say that the state's current bridge design "will delay replacement given its divisiveness, likelihood for a lawsuit, and failure to address the reality of climate change."

On Tuesday, Microsoft ran a full-page ad in The Seattle Times supporting the current bridge plan and saying: "It's Time for Action on the 520 Bridge. Let's Move."

You can read McGinn's letter here.

McGinn wants the $4.65 billion bridge designed to accommodate light rail on the day it opens, and says he's concerned about the size of the proposed Montlake interchange. Three years ago, state lawmakers agreed to build a bridge with two general lanes and lane for carpool and bus traffic in each direction. The bridge, however, would be capable of being expanded in the future to handle light rail.