The New York Times is breaking the news that a new feature for Live Search Maps, called Clearflow, will be announced later today, and the Virtual Earth / Live Maps blog has confirmation.  According to the Times:

The Clearflow system will be freely available as part of the company’s Live.com site (maps.live.com) for 72 cities in the United States. Microsoft says it will give drivers alternative route information that is more accurate and attuned to current traffic patterns on both freeways and side streets.

A system for driving directions that Microsoft introduced last fall was limited, because without Clearflow there was no information available about traffic conditions on city streets adjacent to the highways. Because the system assumed that those routes would be clear, drivers were on occasion sent into areas that were more congested than the freeways.

The new service will on occasion plan routes that might not be intuitive to a driver. For example, in some cases Clearflow will compute that a trip will be faster if a driver stays on a crowded highway, rather than taking a detour, because side streets are even more backed up by cars that have fled the original traffic jam.

Looks like there will be quite a bit more new stuff, as well.  A little hint from the Live Maps blog:

I'll have more details on this feature as well as all the other new stuff later today when the new site is live. I wont's say much more now other than my favorite GeoRSS related feature will be included - Neighborhood subscriptions, which lets you define a chunk of Earth and pluck an RSS feed for all activity on the GeoWeb contained within it.