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Roundabouts - aka Traffic Circles - vs Traffic: Winning?
Awesome things the UK would get:
Cheaper gas
Plutocrats instead of aristocrats
Fahrenheit (you'll thank me for this one)
Greener money
Easier right turns
Better food... and lots of it
Football with brain injuries
Naval superiority
Apple products on launch day
Left turns forever!?
( Last edited by andi*pandi; Dec 11, 2019 at 08:28 AM. Reason: segue from: http://forums.macnn.com/showthread.php?p=4410040#post4410040)
Originally Posted by Waragainstsleep
That's called a roundabout.
Roundabouts are awesome. Except when you start incepting them.
The "magic roundabout". The English love their roundabouts, but this one apparently has them split - traffic moves too slowly to cause any accidents, but throughput is poor:
https://en.wikipedia.org/wiki/Magic_Roundabout_(Swindon)
The new Mac Pro has up to 30 MB of cache inside the processor itself. That's more than the HD in my first Mac. Somehow I'm still running out of space.
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The bedroom communities along the north side of Indianapolis have gone roundabout-insane over the past several years, seemingly bent on replacing every intersection with a roundabout. There are some stretches of roads where there are 4 roundabouts within a mile of road. They're even building (or modifying) bridges over main arteries with roundabouts on either end of the bridge, connecting the cross-street with the artery.
There's one such bridge where, before the roundabouts were added, rush-hour traffic would back-up down the exit ramp from the artery to the cross-street. After adding the roundabouts, the rush-hour traffic still backs-up down the ramp. The engineers' solution? A stoplight at the roundabout.
I should pull my dashcam footage from the roundabout yesterday. The main road goes straight through, each side exit is a side road. I had to go 3/4 of the way through to get to my exit. SUV across from me sat there with no one coming until the moment I got close, then gunned it. I had to hit the brakes and horn.
All threads lead to car talk.
AFAIK the average traffic flow is higher on roundabouts than on traffic lights, so from that perspective, they are the engineer's solution. Of course, I don't know whether that applies to monstrosities like the one Waragainstsleep has found, but I can attest to that.
Roundabouts aren't a panacea, though, against congestion, if the traffic volume is too large, any system will clog up.
That one is "affectionately" called 'the magic roundabout'. I don't know if that reference will land across the pond.
The problem with it is that you don't have a vast amount of time to work out where the hell you're going, and visibility isn't super either so while you're trying to figure out which exits you want, then trying to decipher the road markings and deal with multiple roundabouts at the same time, it can be a pain. I've only ever driven over it a couple of times and I had no idea where I was actually going so I was trying to follow road signs to roughly near my destination which made it even worse.
Guys, this is plainly not political enough. I'm going to have to report you all.
(or, keep posting and I will split this off into its own discussion.)
If only roundabouts were a political issue, we could defeat them all. I'd vote for that.
Politics and going in circles have very little in common.
Why do you hate roundabouts? You don't have to stop when the roads are quiet. Not like your crazy intersection rules.
During busy times, intersections do switch all the time. But during off-hours (especially in rural areas), the signals will default to green on the higher-traffic road. So most of the time, you can drive straight through. No slowing down, no curves, just a clear road.
With a roundabout, you have to play ring-around-the-rosie every single time. Doesn't matter if there are no other cars, or if you're on the more common road. Gotta slow down, navigate around a bend, and hope there are no drunk idiots waiting beyond the curve.
On smaller roundabouts (single-lane), you reach the turnoff you want. But you still have to slow, signal etc and turn, just like an intersection. Slowing any cars behind you (by being rear-ended if necessary). No net gain, you just added a bend to the operation.
So you add a break in traffic flow, a possible blind curve (depends on what's inside the round), and uncontrolled crossing traffic if the roundabout has 2+ lanes.
Further thoughts - roundabouts can make sense if three or more spoke roads intersect. But with just two roads, they make things less efficient all around. They don't actually get rid of intersections, they replace one intersection with 2-4 small intersections. Eliminating the most dangerous turn (left in US, right in UK).
Regular intersection: (reverse L/R for UK)
Straight - drive as normal. Possible stop, then go.
Right - one turn into merging traffic.
Left - one turn against traffic, possibly protected by signal lights.
Roundabout:
Straight - pass through 3 mini intersections. 2x right turns, 2x merging traffic.
Right - pass through 2 mini intersections. 2x right turns, 1x merging traffic.
Left - pass through 4 mini intersections. 2x right turns, 3x merging traffic
Roundabout work best when you have traffic flows that switch back and forth but from two directions ate once. Say in the morning it n>s and E-W but it reverses in the evening. Or most of the traffic is making right turns but the occasional that doesn't.
Slowing from 45 to 30 to go thru a roundabout isn't a big deal. They do have a critical traffic volume were they congest and stop serving all incoming lanes.
That's the real rub.
Their whole point is keeping traffic moving, but actual traffic breaks them.
You will still have a larger net flux of cars compared to an intersection with a traffic light, because you always dynamically allocate capacity. And it is much safer, because cars go more slowly. That's especially important when pedestrians are crossing.
There are other, potential, expensive solutions, but they have their limitations. Back when I was living in Munich, there was one intersection near university that had an induction switch. During the off-hours, the traffic light was controlled by the induction switch. But I was on a bike, which meant that the induction switch would not trigger and I was regularly braking the rules of the road just to get home. Circular traffics are dead easy.
With a roundabout, you have to play ring-around-the-rosie every single time.
You lose a few seconds in the off-hours and gain time during rush hour. Seems like a net benefit to me.
Doesn't matter if there are no other cars, or if you're on the more common road. Gotta slow down, navigate around a bend, and hope there are no drunk idiots waiting beyond the curve.
There are no "idiots waiting behind the curve", because circular traffics are designed so that you can see the whole intersection. (Ok, don't point me to the example Waragainstsleep posted, there are exceptions.)
Everybody is slow in a roundabout, which makes it easier for you to avoid collisions. And it teaches you to play nice. And you avoid left turns.
I understand that they get some getting used to. At first I thought they didn't make any sense. Then the municipality of my school put one on the busiest intersection around, right next to a highway. And it was soooo much quicker to get through the intersection in the morning.
I'm not buying roundabouts are safer for pedestrians without a cite.
Other cars? Yes.
Man...Frankie Boyle is bloody merciless, and funny as hell.
Yeah, I'm not buying that at all. I've yet to encounter a roundabout with any sort of pedestrian crosswalk.
Roundabouts and pedestrians are completely at odds with each other.
Roundabouts keep traffic moving, pedestrians need traffic to stop.
Pretty sure most pedestrians get nailed during a turn. Roundabouts are all turns.
Here's a simpler design which illustrates the same trade-off.
This improves the flow of motorized traffic at the cost of adding hazards to pedestrians and cyclists. Hazards which are far lessened or simply don't exist at a traditional intersection.
Unfortunately, we're stuck deciding whether traffic flow or safety is more important. We can't have both.
As an aside, I posit this is a highly politically charged question.
I thought you had some intersections where you have to stop dead every time, regardless of traffic. Otherwise you can get a ticket. And the cops wait for people to chance it. No?
I'm slightly confused by this question. Doesn't everybody?
Low-traffic intersections do not have signal lights. Common in rural and suburban areas. In such intersections, one road may be the default, with STOP signs on the other road.
If both roads are low-traffic, you can get STOP signs on all sides. In such an intersection, yes, all traffic must stop before continuing. If cars pull up on both roads at the same time, the right-most person has the right of way and should go first.
There are plenty of those in Europe, especially if they are replacing a traffic light.
How so? Roundabouts force cars to slow down and cars can only make right turns. That means impacts are less lethal for pedestrians and what cars do is much easier to anticipate. Unlike a Stop sign, drivers can't "run" a roundabout. That means pedestrians have to deal with cars that have to slow down and only turn right, which is a big win.
In many rural areas roundabouts have replaced stop signs, especially in residential zones. They also serve as speed bumps if you wish, and as I wrote before, you can't "run" a roundabout like you can run a stop sign. Big win all around.
I don't think this is the right way to think about circular traffics: the key is the dynamical allocation of throughput. Pedestrians take precedence, which is not a bug, but a feature.
Except that this design doesn't deliver: yes, it improves flow for cars who want to turn right. But if left turns are allowed, this will block the left lane and significantly slow down traffic wanting to go straight compared to a roundabout. Depending on the traffic pattern, I'm quite sure your design has a lower throughput than a roundabout.
Plus, like you wrote, this makes it way worse for pedestrians and cyclists. For pedestrians you need one or two separate traffic lights. (I wrote two, because here in Japan we do have intersections like that, and pedestrians need to wait three effing phases to cross. And yes, that also means drivers have to pay attention to very complex traffic light patterns.)
Also here, roundabouts are perfect. Cars don't have to technically come to a dead stop and wait for a few Mississippis (which, let's be real, few people do in real life).
you can't "run" a roundabout like you can run a stop sign. Big win all around.
Roundabouts near me are two lanes wide. The right lane is for taking the first exit or going "straight." The left lane is for going "straight" or taking the third exit. These designations are marked by signs and pavement paint.
In the ten years I've lived near these roundabouts, 99 out of 100 times I've nearly been hit, it's been a car jumping lanes (treating the roundabout as a single lane and crossing the solid line into my lane), or a car taking the wrong exit - crossing traffic or cutting off a lane.
The current Google map is outdated - they tore the whole thing up and redid it about a year ago so that the road into the roundabout is no longer a straight shot. I have noticed fewer people cutting through, those they still often cross over the solid line on exit.
Roundabouts lose their appeal the more lanes they have. Most of the ones I have used were 1-2 lanes wide, but mostly 1 lane.
I haven't owned a car for that to comment, but I cycle almost everywhere these days. A good share of the close calls were people at traffic lights who suddenly decided they want to turn left (in Japan = right turns elsewhere). It's one of the few niggles I have with Japanese drivers, they use turn signals very, very late. Sometimes they start turning and then blink. This is a common accident pattern that could be entirely avoided with roundabouts.
I admit I'm totally lost here. The roundabout isn't allocating throughput between motorists and pedestrians in this scenario, the crosswalk is.
( Last edited by subego; Dec 10, 2019 at 12:01 AM. )
The roundabout is dynamically allocating throughput between motorists coming from different directions. Most traffic lights are at a timer, so independently of whether and how many cars are waiting in one direction, they will have to wait a certain amount of time. That puts pressure on the system because you usually have a net traffic flux in one direction or another (e. g. the two directions of rush hours). At roundabouts you don't need to wait for the light to turn green, you can go when there is space. Make sense?
Whenever pedestrians and motorists interact, motorists have to give way, be it at roundabouts or traffic lights. But that is a separate issue IMHO.
Most traffic lights are at a timer ...
That isn't my experience. It's a mix of induction loops and cameras wherever I've paid attention to them. The cameras will go to timers in the event of fog.
the new thing is to use cameras to sense if there's someone waiting to go.
I'm almost positive we're talking past each other.
All motorists are supposed to give way to pedestrians, but what I'm asking to be considered is to what extent they actually do.
To put my argument in the form of a question, does a roundabout make it easier or harder for a motorist to yield to pedestrians compared to other designs?
My guess is roundabouts fare poorly, but I'm curious about your take.
I would agree. Given that roundabouts, ideally, do not stop vehicular movement, they act in opposition to pedestrian movement. Given that I see few, if any, roundabouts in my area that include sidewalks or pedestrian crossing lines, I think the engineers agree.
The one thing I imagine they have going for them is slower speeds make yielding easier, but everything else makes yielding harder. Like, increased throughput of traffic, far more things which need to be paid attention to compared fo a linear design, and that people gun it out of a turn.
Of course, roundabouts also make pedestrians walk farther.
Easier, because cars have to slow down anyway. In a rural and suburban setting, they are great: they are cheaper than traffic lights, little maintenance, and if you space them closely enough, they act as speed bumps (which can be desirable in suburbia).
I don't understand why they should fare worse than intersections.
So that we don't have to go by anecdote, I scoured the internet for information:
- Washington State DoT found huge improvements in safety: less crashes (car-on-car (-37 %) and car-on-pedestrian (-40 %)), less lethal crashes (-90 %!), less injuries (-75 %). They quote studies that show 20-89 % reduction in delays and 56 % reduction in vehicle stops.
- The US Federal DoT extolls the same basic virtues, but they don't quote explicitly where they got their data from. Plus, the data seems to be 10 years old by this point.
- There is a video comparing different designs of intersections. The traditional intersection fares the worst. But it is a simulation and AFAIK only tests a single traffic pattern (and from the looks of things there is not net flow in one direction). Nevertheless, entertaining.
- This page lists (but doesn't link to) a few studies from other countries. All concur with Washington State DoT's findings: significant reduction in fatalities, injuries and accidents. They also mention the recommendation to not go beyond 85 % of the total theoretical capacity since then merging into the roundabout becomes much slower. And a roundabout has about 20 % more capacity in common use cases.
- And I have found a the UK's Manual for Roads and Bridges that gives recommendations as to what type of intersection to build depending on the circumstances.
- I also found a Master's Thesis that was equivocal. It compared a complicated intersection (see p. 20) and tried to replace that with several complicated roundabout designs.
- I also found a mention that roundabouts are harder to navigate and less safe for visually impaired people, even if they are much safer for able-bodied persons.
- An older study had more nuanced findings: the more you know about the traffic flow, the better you can tailor traffic lights to fit it. But importantly, this study only seemed to look at traffic flow, not safety. But it did look at emissions, and roundabouts were performing better.
By design, cars expect to and often have to stop at traditional intersections. This makes pedestrian crossing easier.
By design, cars expect not to and often don't have to stop at roundabouts. This makes pedestrian crossing harder.
Whether the data backs that up or not, it's at least a reasonable hypothesis.
Have you had much experience with roundabouts? (I'm honestly asking, I am not trying to be condescending.)
Cars expect many roundabouts to have pedestrian crossings, and cars then of course yield to pedestrians.
Apart from the higher average speed of cars, regular intersections have many more points of conflict for both, cars and pedestrians. That makes it harder for cars and pedestrians to navigate. With roundabouts, cars have less options, and cars predictably can do only one thing to come your way.
I drive two of them multiple times per day.
Apart from the higher average speed of cars,
I'm not worried about average speed. I'm worried about frequency of zero speed, which is higher with intersections and lower with roundabouts.
With roundabouts, cars have less options, and cars predictably can do only one thing to come your way.
With roundabouts, cars have to decide if they should go or not go. With an intersection, the lights make that decision for you. Indecisiveness and unpredictability are what causes accidents.
Ok. Just wanted to check. Here in Japan, I don't think I have seen a single one, although they were covered in the refresh driver's ed course I had to take when I renewed my license. But the ones in Europe usually come with pedestrian crossings. They often have little islands for the pedestrians so that they have a safe space to retreat to just in case. But with ones where you have less traffic, it is just a regular pedestrian crossing.
Both, as a pedestrian and as a driver, I found roundabouts simpler to navigate and safer, because cars were approaching at a much lower speed. That is especially true in situations where there was previously no traffic light, and you couldn't expect cars wanting to go straight to slow down (even if there was a stop sign). On roundabouts, cars have no choice to slow down (although once I saw tire tracks across the greenery of one notable roundabout, although I doubt this was accidental).
If your point is that your hypotheses are reasonable, ok. But the data doesn't seem to bear that out, quite the contrary, roundabouts seem to be much safer for pedestrians and for cars than ordinary crossings.
Don't get me wrong. I like roundabouts as a concept. I just think their implementation is effed-up in my area. Some roads are becoming more like esses from the numbers of roundabouts along them. There's also an issue with them not being very uniform in construction. Some are fairly large, allowing for a smooth travel through. Others, though, are ridiculously tight, to where you almost have to turn the wheel to its left-hand lock in order to make the turn.
A friend drives a school bus for a nearby upper-crust town which has gone roundabout crazy. My friend says there are many roundabouts along his route that he cannot get his bus through without driving over the curbs. So, that's what he does. The firetrucks do the same thing. Just barrel through over the curbing.
Don't get me wrong. I like roundabouts as a concept. I just think their implementation is effed-up in my area.
That may very well be. I can say that roundabouts became a thing just when I started driving. At first, I thought they were a stupid idea (as I hadn't really thought about them), and it took some getting used to for me and the other drivers. Also the municipalities needed to gain experience with how to use them. The more lanes you have on a road and the more complicated a roundabout, the worse it gets. The simpler they are, the better IMHO, because it really reduces your cognitive load.
I haven't heard of roundabout that were too small for emergency vehicles, but in "Northern" Europe those things aren't usually a problem since everything is standardized. Some of the interior barriers of roundabouts had "soft curbs", which were basically relatively steep inclines. If you had an SUV, you could drive almost straight across it if you wanted to be a d*ck, so that should also help longer emergency vehicles.
I kid you not but the one next to me has 5 lanes. Yes, a roundabout with 5 lanes. I decided to test it yesterday by heading north (from a southern direction) and I have to cut across lanes (there is no such thing as sticking in your lane, the lines have absolutely no meaning), I just couldn't do it. I was forced to head west and then make a right turn later. Combine that with the millions of mopeds here, driving here is horrible.
1. If everybody plays nice, roundabouts are safer.
2. If the roundabout is properly sized for both the traffic and the posted speed of the streets involved, they do not slow traffic throughput substantially. They DO, and are supposed to, slow traffic entering the intersection area, but by doing so they omit stop signs and traffic lights.
3. Stay in your own f'ing lane and you're cool. Change lanes incorrectly, and you're a hazard. While it is not technically illegal to change lanes in an intersection, it is at least foolish and sometimes illegal to change lanes in a multi-lane roundabout.
Here in San Antonio we have had a number of roundabouts appear over the last few years. In every case I can think of, they work well. Mostly, when someone doesn't understand a roundabout, they slow way down on encountering one, so everybody else can avoid them.
While it is not technically illegal to change lanes in an intersection ...
Must differ by state. It was illegal in CA when I took my first drivers test, and presumably still is.
I figure it's illegal because of the ambiguity. You should signal a lane change. But in an intersection, a signal will more often mean "turn". Ambiguity becomes accidents.
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