Please register to participate in our discussions with 2 million other members - it's free and quick! Some forums can only be seen by registered members. After you create your account, you'll be able to customize options and access all our 15,000 new posts/day with fewer ads.
Of the same people who are confounded by managing the FOUR stop intersections
seem to be about 70% as flustered by how to manage the round-about intersections.
That's numerically superior but I'm not sold on being better for us.
I go through a round about daily - It seems to work well given that it replaced a 5 way intersection (previously with 5 stop sign points). Typically the only issues I've noticed are people who FLY through it from one of the entry points. I think some people have made a game of it.
The theory is that traffic flow is maintained better because you don't have a big wad of cars at a dead stop while the light's red.
In practice, there's a big wad of cars at a dead stop waiting to get into the rotary.
I'm not convinced. See West Concord, MA for an example. That rotary stops all traffic for miles in every direction at rush hour.
Roundabouts work best in low traffic areas. We tend to go overboard in the U.S. with traffic lights at low traffic intersections.
The West Concord example is not a low traffic intersection by any stretch of the imagination and is not a good candidate for a roundabout. Yes it gets backed up at rush hour, but there are 5 roads (inc. several with multiple lanes of traffic in each direction) entering/exiting that intersection. A traffic light would not improve it given how long it would take to cycle through each direction. Realistically, the only option for a road like Route 2 in West Concord (which is a highway) is a flyover interchange. A relatively close comparison would be the Route 6/3 interchange at the Sagamore Bridge. It used to be a rotary, but traffic volume caused backups in all directions. A light was not a solution because it still meant traffic backing up in all directions. So they went with a flyover interchange which has vastly improved the flow in that area. This circle in Medford works beautifully for the traffic volume. A light (or series of stop signs) would only create a backup.
One thing that hasn't been brought up is that roundabouts are great because they reduce the chances of a crash. At a signalized or stop sign controlled 4 way intersection, there are 32 potential conflict points where a crash could occur. With a roundabout, the number of conflict points is reduced to 8 (and when there are crashes, the speeds are low so the severity is less)
Of course, like most have alluded, there is a volume threshold above which, roundabouts quickly degrade. It really doesn't take much between a smoothly operating roundabout and one where you have mile long queues waiting to get into the roundabout once you've exceeded that threshold. For a single lane roundabout, that's about 20-30,000 vehicles per day (total for all approaches) and for 2 lane roundabouts, that's about 40-50,000 vehicles per day (the more "left turn" movements there are, the lower that threshold is).
Also I'll note there's a difference between the modern day roundabout and the larger "traffic circle/rotaries" of the past. The modern day roundabout is a lot smaller and lower speed.
The one in Houston at Main/Montrose/Hermann Dr. near Hermann Park is a real challenge in rush hour. Its 3 lanes with people trying to head off in many different directions, so you often have to switch lanes in the roundabout.
Atlanta has one on North Decatur at Emory University that gets horribly stacked up in rush hour evenings during times when the university is in session. There are a bunch of cross walks and so just a couple of students walking shuts down the flow of traffic in all directions. Total gridlock and then it takes forever for cars entering the circle to have a clearing to get in.
This can be useful in certain applications, such as if there's a predictable pattern of higher traffic volume toward a central employment node in the morning and away from the node in the evening.
There's a one-way street in Hamburg, Germany, that quite literally reverses direction at 4 AM - and at noon. The signage changes, it's quite the sight. Drove mapmakers to frustration back in the day of paper maps.
There's a one-way street in Hamburg, Germany, that quite literally reverses direction at 4 AM - and at noon. The signage changes, it's quite the sight. Drove mapmakers to frustration back in the day of paper maps.
I wonder how electronic maps handle it? If the clock in your car isn't correct (Daylight Savings Time or incorrect time zone) can that be used as an excuse for getting the wrong directions?
I wonder how electronic maps handle it? If the clock in your car isn't correct (Daylight Savings Time or incorrect time zone) can that be used as an excuse for getting the wrong directions?
In Germany? The officer will be polite and correct, listen to your excuse with a sympathetic smile, then write your ticket anyway. The signage literally changes, mechanically.
For your amusement (or horror) here is: The More Magic Roundabout.
Swindon only has an array of 5 mini-roundabouts. Hemel Hempstead has 6 in a hexagonal array. Note that relative to the large central roundabout, traffic flows both clockwise and anti-clockwise simultaneously giving a good throughput. Each mini-roundabout is little more than a circle of paint so a long vehicle can go over the top if need be. It typically takes no more than 60 seconds to navigate the whole thing.
My local roundabout is busy only when high schoolers are heading to or from school. Many of them can’t figure it out so either someone will sit there while umpteen cars drive by or else they won’t even slow down and barge into oncoming traffic. There is a landfill nearby so trash trucks are careening through the intersection as well. The rest of the day it works to keep traffic moving. Stop sign would be about the same.
Please register to post and access all features of our very popular forum. It is free and quick. Over $68,000 in prizes has already been given out to active posters on our forum. Additional giveaways are planned.
Detailed information about all U.S. cities, counties, and zip codes on our site: City-data.com.
Please register to participate in our discussions with 2 million other members - it's free and quick! Some forums can only be seen by registered members. After you create your account, you'll be able to customize options and access all our 15,000 new posts/day with fewer ads.
