Franklin Boulevard Roundabouts

[BuildingScout]

Actually don't roundabouts inevitably gum up in heavy traffic, for want of opportunity for yielding traffic to enter the circle?

Yes, this is particularly the case when at least one of the intersecting roads has very heavy traffic. There is a permanent flow of cars along that road, while the ones on the other road wait endlessly for an opportunity to sneak in. In certain circles (no pun intended) this is known at starvation and is one of the main reasons why roundabouts tend to fail in really busy intersections.

By the way, part of my childhood was in a country with plenty of roundabouts and I love them for small intersections. They replace the hideous four way stop. But I also saw them fail first hand in busy intersections and be replaced with traffic lights to the delight of all motorists, and that is before we get into issues with cyclists and pedestrians in said busy roundabouts.

Here's a reference for the academically inclined:

Existing studies on modern roundabouts performance are mostly based on data from singe lane roundabouts that are not heavily congested.

From: X. Chen, M.S. Lee,  "A case study on multi-lane roundabouts under congestion: Comparing software capacity and delay estimates with field data", Journal of Traffic and Transportation Engineering. April 2016.

http://www.sciencedirect.com/science/art...6416300563