Twice this summer, we counted vehicles on the Longfellow. Between June and July, when the lanes of the bridge were shifted and constricted, bicycle traffic was level (well, actually, it rose slightly) while vehicular traffic decreased. I was otherwise occupied this September and didn't get a chance to do a comparable bike count until last week, when I eked out an hour to sit on the bridge.
And the results are so mundane they aren't even worthy of charts and graphics. Basically, the numbers were within a thin margin of error of those from July:
(All values for peak-hour of the count, note that the Longfellow runs east-west; Eastbound towards Boston, Westbound towards Cambridge)
Eastbound Bikes: 308 (July: 298)
Westbound Bikes: 63 (July: 68)
Eastbound Pedestrians: 65 (July: 83)
Westbound Pedestrians: 191 (July: 201)
Inbound Vehicles: 411 (July: 415)
So the bridge, even after two months of people getting used to the traffic patterns, has seen no major changes. Any drop in non-motorized use might be attributable to cooler weather (in the mid 50s rather than the upper 60s) or to random variance. And assuming a normal traffic day, there has been no significant increase in traffic since the bridge has opened.
It's the last piece that I find most interesting. It really speaks to the concept of "induced demand." With the wider Longfellow, we say 800 vehicles per hour traversing the bridge in June. Once the bridge was narrowed, that number fell to 400. There were weeks with dozens police directing traffic, but the number of cars very quickly hit a new equilibrium. People do not seem to need a major education campaign to figure out where to go. If the new roads are gridlocked, they'll find alternate routes. The system has not ground to a halt (although inbound at the evening rush often backs up the length of the bridge). There are too many variables to find out if people have switched to other routes or modes or just not made the trip, but traffic in the morning across the Longfellow has not been the apocalypse.