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.
Not a civil engineer but as far as I know, the space is part of the point. If you keep the roads straight but just draw a circle in the middle, you don't have a roundabout. It only works properly if the drivers have to curve in and out of it.
You could keep the same space I guess by pinching the roads tighter near the entries/exits but I don't think anyone is talking about that.
The UK has mini roundabouts, which are just a painted white circle on the road: <a href="https://upload.wikimedia.org/wikipedia/commons/b/b0/Mini-roundabout.jpg" rel="nofollow">https://upload.wikimedia.org/wikipedia/commons/b/b0/Mini-rou...
Drivers treat them as a normal roundabout by giving way to traffic on the right.
I contest that drivers always treat it the same. They often go through the circle/cut th corner when there is low traffic, and I know at least one mini roundabout where traffic is way less frequent in one direction and the other direction is treated as the "main road" without slowing down.
> You can draw a circle on the road and have “roundabout rules” without the need for any car to even turn their wheels.
If it's physically possible to "skip the roundabout", if it's just a drawing rather than hard barriers, people here (Spain) will just skip it straight up, unless there is a ton of traffic. I think lots of these driving rules and infrastructure has to take local culture into account, as it differs from "We follow laws like our collective lives depend on it" to "We see laws more like suggestions" depending on the country.
That approach fall down flat on nontrivial traffic amounts. Also it requires an actual hindrance in the middle to enforce compliance, and then bigger vehicles won't be able to turn left.
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.
Lvl999Noob · · focus · HN ↗
You could keep the same space I guess by pinching the roads tighter near the entries/exits but I don't think anyone is talking about that.
scrlk · · focus · HN ↗
Drivers treat them as a normal roundabout by giving way to traffic on the right.
leni536 · · focus · HN ↗
I mostly like them though.
embedding-shape · · focus · HN ↗
If it's physically possible to "skip the roundabout", if it's just a drawing rather than hard barriers, people here (Spain) will just skip it straight up, unless there is a ton of traffic. I think lots of these driving rules and infrastructure has to take local culture into account, as it differs from "We follow laws like our collective lives depend on it" to "We see laws more like suggestions" depending on the country.
yxhuvud · · focus · HN ↗
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