According to the MA State Troopers, the vehicle swerved away from Trooper Jay Clement's cruiser at the last moment, sliding out of control. Clement then caught up with the speeding car and stopped the driver, who was not drunk or otherwise impaired. No other information has been released, reports CBS Boston.
The cause for the whole drama was likely that the speeding car was confused by some construction going on in the tunnel. The two left lanes were blocked off by cones (and had been for a mile up the road), but the speeding driver appears not to have noticed.
In short: speeding in a tunnel is a bad idea, and speeding in a tunnel that's also a construction zone is a really bad idea.