I wondered the same thing. I left work around 5:30 and noticed 6 cop cars parked on 57th between 5th/6th. The cars were parked nose-out, reducing 57th to one lane and causing a mess of a traffic jam. The same situation was repeated across from Carnegie hall, and also on 6th Ave between 57th/56th.

The first cop I talked to said it was a "security precaution" and the 2nd said they were running a drill. You'd think they would chose a better time than the afternoon rush hour to completely mess up midtown traffic.