My best friend is a highly experienced civil engineer, specialized in designing intersections. His take on roundabouts:
- They are adored by urban planners because they look nice and you can put a statue or fountain in the middle
- They reduce T-bone collisions
However:
- Small fender benders and sideswipes are much more frequent
- They use way more area
- They work where each direction has an approximately equal amount of traffic. However, usually, one direction (north/south, say) has a larger share of the traffic. In those cases, the bulk of traffic all needs to slow down, downshift, turn a bit in one direction and then turn a bit in the other direction for the minority of traffic that's bleeding on or off the main artery. In those cases, a traffic light is better because the timing can be adjusted to the proportion of traffic from each direction (and more flexible since it can be adjusted over time).
- Finally, they're also (mostly) worse for cyclists and pedestrians.
Essentially, they have use cases, especially in small towns, and they're pretty, but they're usually not the right engineering solution.
For example, the one at [0] regularly sees bendy buses[1] traverse it without any issues. The trick is that there's an outer ring of asphalt and an inner layer of paving stones: cars the asphalt as it is far more comfortable to drive, but longer vehicles like buses and trucks can let their rear wheels ride over the raised paved area as well.
And yes, it works the same when they are completely round instead of oval - this just happened to be the first clear example I came across.
propter_hoc · · focus · HN ↗
- They are adored by urban planners because they look nice and you can put a statue or fountain in the middle
- They reduce T-bone collisions
However:
- Small fender benders and sideswipes are much more frequent
- They use way more area
- They work where each direction has an approximately equal amount of traffic. However, usually, one direction (north/south, say) has a larger share of the traffic. In those cases, the bulk of traffic all needs to slow down, downshift, turn a bit in one direction and then turn a bit in the other direction for the minority of traffic that's bleeding on or off the main artery. In those cases, a traffic light is better because the timing can be adjusted to the proportion of traffic from each direction (and more flexible since it can be adjusted over time).
- Finally, they're also (mostly) worse for cyclists and pedestrians.
Essentially, they have use cases, especially in small towns, and they're pretty, but they're usually not the right engineering solution.
MrSkelter · · focus · HN ↗
You can draw a circle on the road and have “roundabout rules” without the need for any car to even turn their wheels.
paulnpace · · focus · HN ↗
crote · · focus · HN ↗
For example, the one at [0] regularly sees bendy buses[1] traverse it without any issues. The trick is that there's an outer ring of asphalt and an inner layer of paving stones: cars the asphalt as it is far more comfortable to drive, but longer vehicles like buses and trucks can let their rear wheels ride over the raised paved area as well.
And yes, it works the same when they are completely round instead of oval - this just happened to be the first clear example I came across.
[0]: <a href="https://www.google.com/maps/@52.0660752,5.1198197,3a,75y,21.09h,71.52t/" rel="nofollow">https://www.google.com/maps/@52.0660752,5.1198197,3a,75y,21....
[1]: <a href="https://busposities.nl/voertuig/cxx_SolarisUrbino18E_9686" rel="nofollow">https://busposities.nl/voertuig/cxx_SolarisUrbino18E_9686