I wonder what the field of study is called that prepares people for this kind of traffic management/design job and whether is includes average driver/distracted driver/lowest common denominator design considerations. Putting new concrete barriers out without bright paint and reflectors surprises me; people driving their cars right up on them does not.

When my hometown put in their first traffic circle, they incorporated a pedestrian tunnel under one of the entry/exit points. Within the first two weeks, a driver got confused going around the circle for the first time, went over the edge, and dropped their car 8+ feet into the pedestrian tunnel. Fortunately, there were no pedestrians in the tunnel at the time and the driver was ok. They added a guardrail along that edge of the circle.

There were also people going the opposite direction around the circle from the intended flow. And drivers ping ponging between lanes as they went around the circle unsure what lane they should be in, including a cop car I personally witnessed doing it multiple days in a row. And cars that would just plow straight through the middle of the circle until they packed it with brick planters, flowers, and an art installation.

Even if 99.9% of drivers are attentive and safe, 0.1% is a lot of chaos and accidents. I would hope designing for that 0.1% gets a disproportionally weighty amount of attention.