Google Maps has reinstated the feature letting you know how long a trip will take in current traffic. According to Autoblog's sister site, Engadget, the previous algorithm didn't pass muster, so the updated calculations uses both historical and current traffic conditions to arrive at an estimated time of arrival. It appears on the journeys for which information is available beneath the no-traffic estimate.
If the map can't find information on your chosen roads, you can assist The Goog and your fellow travelers by turning on My Location if you have a Google Maps for Android. Your phone – and a bunch of others – will update home base as to your velocities and help fill in those traffic blanks.