OK – that’s a bit harsh. Â They do work as access control and they usually improve traffic flow/reduce crashes. Â But some people still turn left out when they’re “prohibited.”
I was just reminded of this on a count we did at 66th/Barrie in Edina, MN (aerial below).  It’s a beefy 3/4 access with curb and gutter median partially blocking the southbound to eastbound left movement.  We counted the intersection from 6:30 to 9:30 a.m. and 3:30 to 6:30 p.m.  We found 11 people made the illegal left turn lane over the six hour period.  We also had one person make a crazy westbound to eastbound u-turn illegally through the intersection.
Last year we were working on a 3/4 access where we had a lot of illegal left turns. Â We recommended putting pylons down the lane line to physically prohibit the movement, per the figure and photo below. Â The city wanted concrete curb and gutter instead of the pylons and the development project hasn’t been approved yet. Â The pylons have a huge advantage in dealing with storm water – plus I’m a minimalist/experimenter at heart. Â We’ll see what happens on that project.
The punchline is that we need to go to pretty extreme measures for a 3/4 access to block the prohibited left turns. Â When space permits, that should include a triangular median on the approach road to force the cars to turn right.
