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.
> they're also (mostly) worse for cyclists and pedestrians
For cyclists, this is mostly true IMO (depending on implementation), but for pedestrians roudabouts are way better than traffic lights. In the absence of lights, pedestrians have right of way on crossing, so no waiting time, and physically slowed traffic make it safer.
>but for pedestrians roudabouts are way better than traffic lights.
This is ignorant texbook thinking.
As a pedestrian it's far easier to safely time a light, even one without a cross signal, than it is to cross through the un-broken streams of traffic that are entering/exiting a roundabout. You basically have to cross a ways back from the roundabout where the traffic is more like "just crossing a normal road". Which sucks if it's 4-lanes or really busy or fast or there's no sidewalk provision for that (like in the case of roundabouts at highway ramps) and is just a lot more walking to begin with.
For roundabouts that wouldn't be deserving of a light (i.e. the ones replacing 2/4way stops) it's a lateral move.
The point is that traffic streams are not unbroken: when there is a crosswalk and cars are obliged to stop in front of it in the presecence of a pedestrian, then the flow is broken.
Just blundering up to crosswalks because "they have to stop, hurr durr it's the law <foams at mouth>" results in a substantially more hazardous pedestrian (and driver) experience than timing your approach and using your body language so that the drivers know what you're gonna do and can take action to hedge against it.
Especially with heavy traffic, the traffic all slows down, a lot, from the section before the roundabout. Everyone is always in a hurry, so likely 10-25 MPH over the recommended speed (not the speed limit) for the roundabout, and all of them are at a 6 foot following distance.
You are playing with death to step into that. It's no joke. You end up effectively waiting for the upstream light to turn red so traffic can clear and you can cross.
The only solution I've thought of is to put a large grocery cart full of paint buckets at the roundabout for pedestrians to push into the crosswalk without risking their own lives.
> Which sucks if it's 4-lanes or really busy or fast or there's no sidewalk provision for that (like in the case of roundabouts at highway ramps) and is just a lot more walking to begin with.
I mean, it depends on your standards for roundabout. We didn't put highways through town centres so largely highway ramps and pedestrians are mutually exclusive scenarios here. Where pedestrian crossings exist, there's usually (a) an island and (b) 2 lanes prior to the island, splitting to 4 lanes either where the traffic is already slowed or past the island, which makes it much more pleasant than crossing at an equivalent junction. Also as a driver, it means you've cleared the pedestrian area before you have to consider/deal with the cross direction drivers as there's a small waiting area post-pedestrian-crossing/pre-roundabout.
If you're stuck because you already have a highway in your urban core and need pedestrians to safely cross the highway, then you are pretty much limited to overpasses and underpasses.
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.
zeumo · · focus · HN ↗
For cyclists, this is mostly true IMO (depending on implementation), but for pedestrians roudabouts are way better than traffic lights. In the absence of lights, pedestrians have right of way on crossing, so no waiting time, and physically slowed traffic make it safer.
cucumber3732842 · · focus · HN ↗
This is ignorant texbook thinking.
As a pedestrian it's far easier to safely time a light, even one without a cross signal, than it is to cross through the un-broken streams of traffic that are entering/exiting a roundabout. You basically have to cross a ways back from the roundabout where the traffic is more like "just crossing a normal road". Which sucks if it's 4-lanes or really busy or fast or there's no sidewalk provision for that (like in the case of roundabouts at highway ramps) and is just a lot more walking to begin with.
For roundabouts that wouldn't be deserving of a light (i.e. the ones replacing 2/4way stops) it's a lateral move.
TFNA · · focus · HN ↗
agwa · · focus · HN ↗
In the real world, drivers frequently do not stop in the presence of pedestrians.
cucumber3732842 · · focus · HN ↗
paulnpace · · focus · HN ↗
Especially with heavy traffic, the traffic all slows down, a lot, from the section before the roundabout. Everyone is always in a hurry, so likely 10-25 MPH over the recommended speed (not the speed limit) for the roundabout, and all of them are at a 6 foot following distance.
You are playing with death to step into that. It's no joke. You end up effectively waiting for the upstream light to turn red so traffic can clear and you can cross.
The only solution I've thought of is to put a large grocery cart full of paint buckets at the roundabout for pedestrians to push into the crosswalk without risking their own lives.
Macha · · focus · HN ↗
I mean, it depends on your standards for roundabout. We didn't put highways through town centres so largely highway ramps and pedestrians are mutually exclusive scenarios here. Where pedestrian crossings exist, there's usually (a) an island and (b) 2 lanes prior to the island, splitting to 4 lanes either where the traffic is already slowed or past the island, which makes it much more pleasant than crossing at an equivalent junction. Also as a driver, it means you've cleared the pedestrian area before you have to consider/deal with the cross direction drivers as there's a small waiting area post-pedestrian-crossing/pre-roundabout.
If you're stuck because you already have a highway in your urban core and need pedestrians to safely cross the highway, then you are pretty much limited to overpasses and underpasses.