and 12-times as expensive roundabouts on exit and entrance ramps.
12-times as expensive roundabouts
It is not just the cost of roundabouts that are beneficial to the left (the road builders send a good chunk of that money back to the Dims). Other advantages are:
1) It takes more land out of private hands (every little bit helps)
2) It frustrates drivers into (hopefully in their eyes) getting on to public transportation instead of private vehicles.
3) It gives DOT personnel a feeling of power because they can force these on the people who pay their salaries.