The new service's software technology, called Clearflow, was developed over the last five years by a group of artificial-intelligence researchers at the company's Microsoft Research laboratories. It is an ambitious attempt to apply machine-learning techniques to the problem of traffic congestion. The system is intended to reflect the complex traffic interactions that occur as traffic backs up on freeways and spills over onto city streets.

The Clearflow system will be freely available as part of the company's Live.com site 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.