Ask questionsAutomatically lower speed limits on roundabouts [Suggestion]
Many people use highways for roundabouts, as there's no other 3-lane one-way road in vanilla, or use 80km/h highway ramps for small residential roundabouts as the only 1-lane road in vanilla.
But the roundabout going faster than the connecting roads is both unrealistic and less efficient -- having the speed limit lower makes it easier for traffic to merge onto the roundabout (less time accelerating means they can fit into a smaller gap, and the same distance of gap becomes a longer-in-time gap) and allows for more traffic to be on the circulating roadway at a time.
So it would be nice to have an option for the roundabout auto-setup to also set an appropriate speed limit based on the size of the roundabout.
How fast should it be? Well, the FHWA's roundabout technical summary suggests speeds of 25-50km/h, for different sized roundabouts, and we know that a=v²/r, so it seems plausible for the speed to be linear in the square root of the radius.
Playing with the numbers a bit, setting the speed limit to 4√r (with r in meters and speed limit in km/h) seems plausible
|radius (u=8m)||speed limit (km/h)|
So here's a concrete suggestion for how this could work, as a probably-close-enough approximation:
Other estimates for the radius could be 1/2π of the length of the roundabout, or anything else that's easy for you get and about-right for anything that's about-circular. (If the speed limits are a bit off for a "wonky-about" I wouldn't really care.)
Answer questions scottmcm
Thanks, folks! I'm excited to try this when 11.6 comes out!
Related questionsNo questions were found.