Traffic Congestion - a taxing solution
Gary Becker, Nobel Prize winning economist has suggested a tax levied differently based on time of day. Read more in his blog post - http://www.becker-posner-blog.com/archives/2006/02/the_solution_to.html
There are positive incentives like we have here in Microsoft for car pooling etc but there are still way too many cars on the road so maybe a tax might be worth trying as well. I know that I'd then use the bus (free) or car pool.