What is a "traffic drag"?

Question

Getting on 95 out of Baltimore today, traffic on the ramp came to a standstill. I could see that about 1/2-mile of traffic was stopped, or nearly-stopped, but everything seemed clear beyond the bend in the road. There were quite a few official vehicles (flashing lights, flashing signs, etc), which isn't too far out of the ordinary -- there's always some construction going on. The traffic reporter on the radio said three times (I sat in traffic through 3 reports!!) that there was a 'traffic drag' in progress. Eventually, the standstill just disappeared -- I didn't see any rhyme or reason.

Answer 1

(flashing lights, flashing signs) should be a sign of what a drag is just a normal slow down when one slows down then everyone behind has to slow down also think that was what he was talking about