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Intersection Design - Bypass or Stoplight

04/19/2012 12:29 PM

I suppose the choice is up to each city council as to how to construct intersections of 4 lane roads, but I wonder how much influence other people have.

Most of the intersections in my area use stoplights for traffic control. I have noticed that frequently the traffic engineer has programmed the light to give excessive priority to side streets where the 4 lane has a much higher speed limit than the side street. This results in frequent occasions where 10 or 20 or more cars have to stop, wait, and then accelerate to cruising speed again all because one car wanted to cross the intersection or join in the perpendicular traffic flow.

For areas where the speed limit is above 45 MPH I have observed that the amount of gas consumed in regaining the cruising speed amounts to approximately 1 gallon for every group of 10 automobiles per stop. This is an enormous waste considering how often this happens. We are paying many times over for the cost of a cheap approach to road way design. My question is how to make change to a more sensible design happen?

I really like the service road design around the faster highways that I have seen in Dallas, Boston, Baltimore and other places. It seems that those designs are so much better because the highways mostly don't have any traffic lights.

I wonder how much we could reduce our oil consumption if we invested in better road designs? Think of the jobs that would generate!!! What does it take to make that happen?

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#1

Re: Intersection Design - Bypass or Stoplight

04/19/2012 12:42 PM

Common sense will help.

Traffic Roundabouts: Do They Work In Your City? (live in, safety ...

"They" recently built a new freeway in my area. At two of the interchanges they built traffic round-abouts instead of installing lights.

I thought, "what a dumb thing to do."

I now think it was a brilliant idea, cause I never have to stop there, unless there is a good reason.

Look into these!

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#2

Re: Intersection Design - Bypass or Stoplight

04/19/2012 1:01 PM

Round-a-bouts have really taken over in our area, It takes more time to build but is cheaper over all to maintain.

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#13
In reply to #2

Re: Intersection Design - Bypass or Stoplight

04/20/2012 8:17 AM

A true RA also does not use any electricity (forgetting lighting) and works even in a mains failure....though the UK has resorted to lights at times of peak traffic when some RAs get completely overloaded.

If it can be built large enough with a large grass area in the middle (some UK ones are HUGE), they can be used to feed sheep or cattle if fenced correctly.

For junctions with little space in the UK (built up areas), they paint a white circle in the middle (which you are allowed to drive over) to show that it is a RA and to set the priorities. They have been in use for a great many years, my guess is "more than 40 years".....tried and true.

A study here in Germany shows they cost much the same as a junction with lights to build, but maintenance is cheap and simple.

Also far fewer "possible points of contact/accident", and even those show that the vehicles are almost traveling in the same direction, so not likely to kill anyone, just mess up the metalwork a bit.....whereas normal junctions have points that are 180° opposed.

Also, Europe does not have (as far as I am aware), any "all round stop" junctions as in the US, which appear to be a big source of problems there....here one road always has priority/or a tiny RA....I don't know if alround stop junctions are simply forbidden or not. Also a thought.

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#3

Re: Intersection Design - Bypass or Stoplight

04/19/2012 1:07 PM

Many traffic departments have a special department which accepts recommendations from concerned citizens regarding this sort of problem.

We have a pair of stoplights here on each side of a raised highway which serve the off ramps. There is another pair of stoplights 100 feet away from each of those stoplights serving side roads. This area was almost impassable most of the time.

I wrote a stoplight "sequence of events" and sent it in for the 4 lights. After review, they changed the sequence to my program. Didn't solve the problem entirely, but helped a great deal.

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#4

Re: Intersection Design - Bypass or Stoplight

04/19/2012 1:07 PM

Traffic studies?

Get out there with your clipboard and clicker. Start at 5:30am, when most roads start to see an increase in traffic, and finish at 7:30pm. Count the vehicles travelling in all directions and link those results to the time period[s] in question. Repeat for seven days.

Take those results to your planners.

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#5

Re: Intersection Design - Bypass or Stoplight

04/19/2012 1:12 PM

Go with the flow....in a roundabout way...go without stopping....gets better each day...

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#6

Re: Intersection Design - Bypass or Stoplight

04/19/2012 3:12 PM

There have been some roundabouts built near where I live (north of Atlanta) and I like them a lot. I find them very easy to use and they control traffic very well; but these only accommodate the intersections of 2-lane roads, not 4-lane roads.

Another type of intersection being considered near here is the Continuous Flow Intersection. In this case, it is for the intersection of a 4-lane highway and a heavily used 2 lane road. It is all at-grade, i.e., no flyover bridges/overpasses/underpasses. The left-turn lanes are broken-out and are crossed-over the oncoming lanes with a separate set of lights well ahead of the intended turn. The theory is that this improves the flow in all directions. There are already working versions of this type of intersections in some areas.

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#9
In reply to #6

Re: Intersection Design - Bypass or Stoplight

04/19/2012 5:49 PM
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#10
In reply to #9

Re: Intersection Design - Bypass or Stoplight

04/19/2012 6:02 PM

4 lanes/4 directions here in Arizona, too.

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#12
In reply to #9

Re: Intersection Design - Bypass or Stoplight

04/19/2012 11:13 PM

As for the top picture, the traffic circles tend to be designed with a main diameter that is a little too small for the typical traffic volume level that requires drivers to watch a few too many things all at the same time. They tend to be a little nerve-wracking with only a few cars on them at one time. Thus, they are generally a poor idea when undersized for the amount of traffic they are intended to handle...

As for the bottom picture, the traffic circles are obviously a terrible idea because they require drivers to additionally change lanes in congested conditions in addition to avoid those near them who also are trying to merely stay alive in the confusion.

Four-way stops, with traffic lights, are relatively easier on the driver's nervous systems than traffic circles.

For the traffic volume indicated in the lower picture, parallel streets in opposite directions, with well-timed, signalized intersections would a much more (civilized) solution. Allowing only right-hand turning at said intersections could be a further improvement... I bet the insurance companies would like such a combination of solutions MUCH better too...

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#14
In reply to #12

Re: Intersection Design - Bypass or Stoplight

04/20/2012 8:24 AM

The gridlocked RA is demonstrating where due to other problems on connecting roads, they can fail. But it is the problem of the other "problems", not the RA itself.

This is seen in the UK and they have so called "Magic Roundabouts" where the traffic can travel in both directions around the main island. They scare foreigners though!!!

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#19
In reply to #14

Re: Intersection Design - Bypass or Stoplight

04/21/2012 4:33 PM

Apparently, the locals have used the traffic circle shown in the second picture often enough to become accustomed to it's (four "choke points" and other) characteristics... but how long does it take each time to unravel such a (traffic knot)?... and what quantities of atmospheric pollutants become relatively concentrated from just one such a source-condition?... each time?... how many times per day?... how many days per week?... how many weeks per year?... for how many years now?...

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#18
In reply to #9

Re: Intersection Design - Bypass or Stoplight

04/21/2012 2:28 PM

This is the way to go....but it would be nice if when you were approaching this maze, that you could press in your route via GPS and have it guide you through...You miss a turn here you could be circling for a while...

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#20
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Re: Intersection Design - Bypass or Stoplight

04/21/2012 4:50 PM

Too bad the main "traffic arteries" shown (where?) are not just two main thoroughfares intersecting at (nearly) right-angles, because then a simple cloverleaf intersection would be less confusing, and less costly to construct, and have only two levels of roadway. That way, if an earthquake struck, only one level of vehicles would be in danger of being crushed below...

The picture appears to show five levels, which, if a big enough earthquake struck close enough, could cause said intersection to become a "five-ply"...

But until then, the traffic keeps on moving with significantly less stress imparted to the drivers than would be by even a large-diameter traffic circle. So, yes, I do generally agree. This is the better way to go.

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#22
In reply to #18

Re: Intersection Design - Bypass or Stoplight

04/22/2012 5:20 PM

I have a Tom Tom, we have not been together (I think!!) over this spaghetti junction, but over many others and it has ALWAYS guided me correctly.....I am sure other makes of GPS are equally as good.......

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#21
In reply to #9

Re: Intersection Design - Bypass or Stoplight

04/21/2012 6:42 PM

That second picture looks like a You-Tube in which nothing happens for hours.

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#7

Re: Intersection Design - Bypass or Stoplight

04/19/2012 3:23 PM

Those of you that like roundabouts must not have lived in New Jersey, if you check it out, they are called "traffic circles" there. They work well until traffic volume reaches a tipping point, then they are deadly.

If I had my druthers, I would vote for jug handles,

The service road system pushed by the OP is excellent but expensive in dollars and acreage. It is murder to retrofit, lots of eminent domain.

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#8
In reply to #7

Re: Intersection Design - Bypass or Stoplight

04/19/2012 4:00 PM

"Those of you that like roundabouts must not have lived in New Jersey"

Never have, never will.

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#16
In reply to #8

Re: Intersection Design - Bypass or Stoplight

04/20/2012 6:56 PM

Amen to that !

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#11

Re: Intersection Design - Bypass or Stoplight

04/19/2012 11:02 PM

Interestingly it is usually determined by city traffic department based on a variety of demographic factors.

Towns with older populations use 4 way redlights because they are less challenging than roundabouts. They also intentionally de-synch the lights to force stops at each one to slow the pace of traffic.

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#15

Re: Intersection Design - Bypass or Stoplight

04/20/2012 2:49 PM

Until recently, I hated any intersection with a round-a-bout or circle. But not far from my home, on a back road with a fairly low speed limit, they installed one that really makes sense. It allows drivers to move through without stopping and makes for better flow through the intersection.

There are several I've been through that are entirely ridiculous. They don't belong on a high speed thoroughfare. Having to slow down to get through and accelerate past defeats any attempt at saving fuel.

Of course there are always those drivers that can't figure out that, once you are in the circle, the other traffic should yield to you, not the other way around...

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#17

Re: Intersection Design - Bypass or Stoplight

04/21/2012 11:25 AM

I agree with your observations. These are considered the "smart" traffic lights that shut down four lanes of traffic traveling fifty-five miles per hour for one car that would have already been gone, if they didn't have a red light.

A simple short term solution would be to locate more sensors 'upstream' from the traffic signal so that the light change was more of a democratic decision allowing the more heavily traveled thoroughfare to have longer green lights and the single car would have to wait longer. At least this would lessen the probability that multiple cars and tractor-trailers would be brought to a grinding halt because one car tripped a sensor on a side road.

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