Traffic Stop on Franklin Avenue at Sterling

Around 11pm tonight we saw a group of 5-6 police officers stop a car at the intersection on Franklin Avenue at Sterling. As we kept walking we saw that people were asked to get out of the car, people were handing over papers, etc...
Cars were backed up at least 2 blocks and then started honking horns, etc. because of the stop.

We had assumed it was a check point of some sort (sobriety check points were very common in my suburban driving experience from 16-18years old) but we watched for 2 traffic light cycles and no one else was stopped.

Anyone know what happened? The police kept standing at the corner like they were going to stop a car, but we didn't see them do so. Was it random?

Just curious, really.