Usually, I bike through that intersection quickly and don't get a chance to witness any misbehavior. But I figured I had a duty to be an informed whiner, so I sat there today for 15 minutes to count cars and take notes, from 9:53 to 10:08.
I saw no pedestrians or cyclists crossing this intersection. It was raining, the intersection is ped-unfriendly, and there's not really any place that anyone would want to go to or from, so that's not a surprise.
I could only estimate the number of cars travelling inbound on 5th avenue and continuing either through, or down the ramp to the Blvd of the Allies. They came in platoons, while all the interesting stuff was happening at the stop signs. I estimated approximately 130 of these.
At the stop sign on Robinson inbound to 5th avenue, I counted 21 cars. Of that 21, 7 came to a complete stop before proceeding. 14 rolled through it, none slower than a fast walk, some at approximately 20 mph. Of the 7 that stopped, the number that did so when there was no oncoming traffic down 5th avenue was 0. In other words, all the drivers treated this as a yield sign.
While illegal, I can't say that it was unsafe, and there really should be a yield sign there instead of a stop -- (except that if there was a yield sign the motorists would treat it like a yellow light and go faster).
At the stop sign from 5th Avenue onto Robinson, I counted 21 cars. 4 came to a complete stop before turning right, 16 made a rolling right turn. Most of those slowed to a brisk walking pace. There was no conflicting traffic at the intersection, so there was no "reason" for the 4 to come to a complete stop. I think that the stop and the slower speed in general, as compared to the other stop sign, can be explained by differences in the geometry of the intersection and the nature of the destination.
The interesting sign was the one for through traffic onto Maurice. I counted 3 busses making a left turn onto 5th, which they are allowed to do. Though in order to do so, they have to make some gawdawful maneuvering contortions that only work because there is almost never any conflicting travel from Maurice to Robinson.
I also counted 4 vehicles making an illegal right turn in order to reach the ramp to the Blvd.
In addition to those 4, I saw two really interesting maneuvers. I witnessed one driver go legally straight through onto Maurice, then turn around, make a right turn into the bus lane inbound on 5th, drive down a block, pull a U-turn in the road and then come back inbound on 5th to the ramp to the Blvd. I think he was following a GPS. Google Maps recommends something impossible which might be the reason I saw the driver of a black VW drive down to the end of the Robinson-5th interchange, realize he was stuck, throw it into reverse and back all the way up to the "busses only" interesection, followed by the illegal right onto the Blvd ramp.
Out of all these illegal, aggressive, scofflaw motorist behaviors, I have to admit that I saw nothing that I would call truly unsafe in and of itself. You could stand on the "broken windows" theory, I suppose, or you could count cars for a longer period or at a different time of day.