[T.B. Yoits]

The right-turn ramp concept does sound safer. Do you have an idea of the cost difference between the types?

My understanding is that the real estate needed is the biggest factor, not the grading, substrate, curbing, and paving.

[minnesota_bound]

They do take up a lot more space and as far as I can tell will create more accidents.

Photo of roundabout.
https://streets.mn/wp-content/uploads/2017/11/07Are-Roundabouts-Safer_535.jpg

Here is one by my old high school in Crystal, MN. I just noticed it earlier this year on a map so it must have been built not long ago. It looks like they have removed a house on the right. I bet many accidents have happened there.
https://www.google.com/maps/place/Douglas+Dr+N,+Crystal,+MN/@45.0035566,-93.3606001,406m/data=!3m1!1e3!4m5!3m4!1s0x52b3341a5d149891:0x69ce397bf717688a!8m2!3d45.0271346!4d-93.3600922?hl=en