They make people on the main road slow down, which is a feature, not a bug. What you mean is that they're the most efficient at what they do when the traffic is comparable. They only reduce accident at the expense of a slightly lowered throughput if the traffic is highly disparate.
> Right but it's not like a 4 way stop is going to perform better.
A 4 way stop does perform better than a roundabout given highly disparate traffic volumes, because roundabouts suffer from resource starvation in that scenario, but 4 way stops are starvation-free.
If this is the case you can install stop lights and traffic sensing at roundabout ingress points, you can also provide a "turn right" lane that bypasses the roundabout entirely. Intersections are dangerous.
> If this is the case you can install stop lights and traffic sensing at roundabout ingress points
But those options are a lot more expensive and need a lot more maintenance than just a regular roundabout or four way stop.
> you can also provide a "turn right" lane that bypasses the roundabout entirely.
How would that work? Consider a 4-way roundabout, where there's a constant flow of cars from west to east, and one car from the south that wants to go north but can't because of the starvation problem. None of the involved cars would want to use a "turn right" lane.
Putting a stop sign or traffic light in your scenario will just cause traffic jams. If the density is low enough to allow flow with a gap created by a stop sign, without causing traffic jams, then there will also be gaps for the secondary flow.
If the volume is disparate, then the road with less traffic can wait... kind of like a stop sign! Except the road with more traffic won't back up and cause massive problems.
If the traffic intensity of the main flow is so high, that there are never any gaps, then it is near the saturation and will cause traffic jams anyway. Which first needs to be fixed anyway and second will also cause gaps to be created again, because the main flow comes to a halt.
