taking on the police baricade

I won't misrepresent myself by implying I know anything about police work.. I'm sure there are a ton of things that cops do which come as second-nature but there are a ton of things they tend to do which makes absolutely no sense to me.   The last few times I've driving across the Brooklyn Bridge into Manhattan, I've noticed one of those little three wheel police cars sitting in the left lane on the approach.  Now I may not know enough about racial profiling, crime scene investigation or following a hot-lead but I do know something about basic physics which means that if you have two lanes of traffic flowing onto an approach and you decide to block a part of one, you will get a bottleneck effect.  What this will mean is that there will be traffic which will backup all the way to Atlantic Avenue.  Now if there was a good reason for this like maybe the cops were doing some kind of check before the cars got onto the bridge, than I might see some value to it…but when the cop stationed to the job is just sitting in his tricycle jitney talking on a cell-phone than I guess I fail to see the value..