# Diverging Diamond Interchange



## MrFSS

OK all you road engineers. Here is a new type of highway intersection. What do you think?

*MODOT SITE*

*MORE INFO*


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## Green Maned Lion

Saves money, reduces speed, confuses the **** out of people. I think its the dumbest idea in the history of road engineering.


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## jackal

Innovative concept. It appears to possibly reduce the number of light cycles needed, as there are no signaled left turns. It will likely be more than a tad confusing to the average motorist, however, and I'm not sure it has any advantages over a SPUI (Single-Point Urban Interchange) in new construction (although for renovating existing construction, this might be more cost-effective because SPUIs would likely require a new, longer bridge for the overpass).


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## PRR 60

Pretty clever. It markedly increases the capacity of the traditional diamond interchange while eliminating the huge land need of going to a full clover leaf. Urban construction all but precludes the ability to get the land for a full clover leaf, so this is not a bad alternative for capacity enhancement. Properly signed and striped, it should not be confusing. You simply follow your lane, obey the signals, turn left to go left onto the interstate and right to go right onto the interstate. Even a caveman could do it.


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## Green Maned Lion

It wouldn't confuse ME, although it would annoy me do to its inherent slow speed. However, PRR, perhaps you haven't noticed the number of below-caveman drivers there are on the roads?

Let me cite an example. There is an intersection near my house where a main road, mostly one lane each way, 45 mph speed limit, intersects with a divided and shouldered 2-lane each way route.

It has a simple set up, in my mind. The 2-lane each-way divided and shouldered, which we will now call 35, runs north-south, whilst the other, which we will now call Deal, runs east-west. On the southern two corners, there are 4 jug-handles. The jug handles operate as follows:

1) from 35 North to Deal, allowing for either east bound or, via a left turn though traffic, west bound travel on Deal road. The jughandle is fanned at the end to allow the east-bound to go while west-bounders sit and wait for traffic openings.

2) From Deal East to 35 North.

3) From Deal East to 35 South

4) From 35 South to Deal East

As Deal approaches 35, it fans out. There are two West bound lanes on Deal going for about 2 tenths of a mile leading up to the intersection east of it, but it immediately merges west of the intersection. From Deal East, it becomes 2 lanes about 300 feet west of the intersection, and continues as two lanes past jug handles 1 and 2, to the next light, .22 miles east. The right lane becomes a turn off into that intersection only. 35 is two lanes and a shoulder/merge in all cases.

From 35 South, it is legal to make a right turn to Deal West, but no right-on-red- this is the only allowed turn off of 35 at this intersection. Right turns Deal East to 35 South, is weakly discouraged via on-road paint only.

Left turns from 35 onto Deal in either direction is strictly prohibited, and doesn't happen anyway. From Deal West, it is legal to make a left turn from the left lane, but it is not a left-turn-only lane. From Deal East there are approximately 8 signs and road paint markings indicating a left turn is NOT allowed.

Despite this, atleast once every 3 light-cycles, one person attempts to make a left hand turn.

Granting this, how can you expect people to not screw up on this intersection?


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## jackal

Green Maned Lion said:


> It wouldn't confuse ME, although it would annoy me do to its inherent slow speed. However, PRR, perhaps you haven't noticed the number of below-caveman drivers there are on the roads?


If there is one thing I've learned working in the customer service sector, it's that the general public is, quite frankly, stupid. There is truth to the now-old adage (popularized by Despair, Inc., I believe) to "never underestimate the power of stupid people in large groups," or as my old After Dark screensaver used to tell me, "The IQ of a group is the lowest IQ of a member of the group divided by the number of people in the group."

There's a roundabout that was built a few miles from my house a good three or so years ago (second one in the state), and still to this day, there are people who approach it when there is not another car in sight and stop before entering. And then you get the real idiots who actually stop _in the middle_ of the roundabout because they think they have to yield to the people who are stopped and waiting to enter. I swear, these people should have their licenses revoked...

(I'm only less slightly annoyed by the super-cautious people who wait to enter the roundabout until there are no cars in it or approaching it--the whole reason it works so efficiently is because you can enter it in even a small gap in the traffic--but at least I understand why they're being cautious. People who just stop for no reason are just dumb.)


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## gswager

Not safe in the dark- can't find the faded marker lines on the road, even rain, and even the drunken drivers hitting head on.

EDIT: Never mind, found a more details from the second link on the first one (MrFSS.)

For those who visit Texas, did you screwed up with the frontage roads and interstate highways, esp. in the rural areas?


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## the_traveler

jackal said:


> There's a roundabout that was built a few miles from my house a good three or so years ago (second one in the state), and still to this day, there are people who approach it when there is not another car in sight and stop before entering. And then you get the real idiots who actually stop _in the middle_ of the roundabout because they think they have to yield to the people who are stopped and waiting to enter. I swear, these people should have their licenses revoked...


I agree it is stupid to stop when there is no one else in sight, but as far as stopping in the roundabout, it depends on the laws of the state you're in (and what you're used to in your home state).

A good (?) example is Rhode Island and Massachusetts (right next to each other). In RI, the car already in the circle has the right of way and cars entering must yield to them, but in MA I understand it is the opposite (cars entering have the right of way).

I know very few cars from FL or NY are in AK, but maybe the drivers are tourists from out os state!


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## PRR 60

jackal said:


> ...There's a roundabout that was built a few miles from my house a good three or so years ago (second one in the state), and still to this day, there are people who approach it when there is not another car in sight and stop before entering. And then you get the real idiots who actually stop _in the middle_ of the roundabout because they think they have to yield to the people who are stopped and waiting to enter. I swear, these people should have their licenses revoked...
> (I'm only less slightly annoyed by the super-cautious people who wait to enter the roundabout until there are no cars in it or approaching it--the whole reason it works so efficiently is because you can enter it in even a small gap in the traffic--but at least I understand why they're being cautious. People who just stop for no reason are just dumb.)


That's because where you live they are called "roundabouts". I live in New Jersey where they are called traffic circles, or for short, "circles". The rules for New Jersey circles: there are none. Every man (or woman) for him (or her) self. You enter the circle at the highest speed possible, preferably with a dozen cars and a truck or two with you, and dare anyone to get in your way. I love New Jersey, I love circles, and so do the local body shops!


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## Green Maned Lion

I've never had a problem with NJ traffic circles, although that one in Cherry Hill was a killer the one time I went through it.


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## jackal

Ah, that's right--the developer's site, http://www.alaskaroundabouts.com/, does mention the differences between traffic circles and roundabouts. (For the first two years, they had several black-on-orange construction signs with that website printed on it at each entrance--presumably to try to clue the dumb drivers into how to properly use it. Didn't work...)

And I'm pretty sure the people who stop aren't stopping because they're familiar with traffic circles, since they always approach the roundabout _really_ slowly and with great trepidation. There's no excuse: they're just plain dumb.

(I'm sorry--I'm not usually so negative or cynical, but dumb drivers and dumb customers are the two areas that I can't help get on my nerves...)


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## MrFSS

As I keep telling my wife and friends, there are a lot of folks out there who shouldn't even have a driver's license!


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## Joel N. Weber II

the_traveler said:


> A good (?) example is Rhode Island and Massachusetts (right next to each other). In RI, the car already in the circle has the right of way and cars entering must yield to them, but in MA I understand it is the opposite (cars entering have the right of way).


I'm pretty sure the Massachusetts law matches your RI description.

Regarding merging into small gaps in traffic, I've always thought that my primary responsibility as a driver is to make sure I don't cause an accident, and that if I need to slow down to meet that responsibility, or wait for a larger gap, that making sure I don't cause an accident is The Right Thing. For a while I owned a non-turbocharged diesel, which does not accelerate nearly as well as anything else on the road. More recently, I have not owned a car, mostly taking trains and buses and renting cars on rare occasions, which means that I am out of practice driving in general and not necessarily terribly familiar with the exact acceleration and steering characteristics of whatever car I happen to be driving. Also, much as one who is renting a car should take the time to adjust the mirrors correctly, mirrors on a car only driven by one person seem to be more likely in practice to be well adjusted on any given trip.


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## Green Maned Lion

I drive a non-turbo diesel myself, John. I rarely see circles with anything more than a yield sign. My approach to them is approach them going the speed limit, with my exhaust brake primed and one foot over the brake (I have a long history and practice- primarily competition- with two-foot driving, and it isn't for everyone), but so far, I've yet to need to do more then adjust my speed down or up a bit to merge into traffic. Also, the two foot approach is not important if you don't have an exhaust brake. The exhaust brake operates when the throttle closes.

If you drive a car with limited acceleration, it is wise to learn how to avoid deceleration when possible. For example, maintaining speed in corners up to about 7/10ths of your cars handling limit, as opposed to the normal 1 or 2/10ths most people seem to do. People who aren't comfortable with that should probably get a car with better pickup.


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## GG-1

Aloha

And Hawaii DOT decided "roundabouts" would slow traffic on local streets, so .... in the middle of blocks on streets that had reputations for speeding there are bulges in the road and a circle in the middle. guess what, now the speeders crash into something as they drive over the curb of the circle as they loose control of the car.


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## AlanB

GG-1 said:


> Aloha
> And Hawaii DOT decided "roundabouts" would slow traffic on local streets, so .... in the middle of blocks on streets that had reputations for speeding there are bulges in the road and a circle in the middle. guess what, now the speeders crash into something as they drive over the curb of the circle as they loose control of the car.


Actually about 35 years ago or so, New Jersey years ago decided that too, not to mention that they felt that circles where inherantly too dangerous. So they embarked on a program to eliminate all the traffic circles in NJ. Maybe 15 to 20 years ago, just about the time they had managed to eliminate probably 85% to 90% of the circles, they changed their mind. So they started putting circles back in many places, when they found that the actually improved flow, especially when traffic lights were added in major high volume circles.


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## Green Maned Lion

Actually, I'd say its partially because they did one heck of a bad job on removing the buggers. Take the intersection resulting from the removal of the Eatontown Circle at the intersection of Wall, Route 35, and Route 36. Take it. Please take it. I don't want it. We don't want it, nobdoy wants it. We'll give it to you. We'll _PAY_ you to take it.


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## AmtrakWPK

In these days of increasing fuel costs and decreasing supply, and India and China rapidly increasing their use of it, ANYTHING that can avoid traffic lights, where half the traffic is always sitting idling away precious gasoline, should be done. So instead of designing intersections with traffic lights (computer programmed to maximize flow or not), I would MUCH rather see the Interstate at that interchange elevated high enough that those crossing roads (with the lights) could simply be stacked, with NO traffic lights required, or some other solution that would not require an interruption of traffic flow. Use of traffic lights and stop signs should be limited by law because of the truly staggering waste of fuel that they cause, and limited to places where they simply cannot be avoided. I don't see this as one of those.


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## jis

the_traveler said:


> A good (?) example is Rhode Island and Massachusetts (right next to each other). In RI, the car already in the circle has the right of way and cars entering must yield to them, but in MA I understand it is the opposite (cars entering have the right of way).


If the Massachusetts law is as you say it is then the traffic engineers in Massachusetts should go and get their heads examined, or at least brush up on their flow control theory. That setup is inherently prone to create deadlocks.


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## Green Maned Lion

In New Jersey, if it is not signed, and it usually isn't, its simply a game of chicken at circles. People familiar with them fly around them like you wouldn't believe, people who aren't can get pretty shakey. There are no specific rules one must follow.

They are very effective at moving traffic, but they do have a pretty bad accident rate.


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## George Harris

MrFSS said:


> OK all you road engineers. Here is a new type of highway intersection. What do you think?
> *MODOT SITE*
> 
> *MORE INFO*


Whatever the guy that dreamed up this thing had been smoking sure wasn't tobacco.

You have to design roads for operation by the simpleminded, and this is not.

The only operational advantage is that the people coming off the freeway do not have to go through a light to ge onto the crossing roadway. The advantage is slight as there is still the light at the other side of the freeway.

I see this slight advantage as being overshadowed by the double swap of the crossing street. Since this is very abnormal, the potential for wrong side driving is greatly increased.

Normally during low traffic hours the lights at a signaled diamond interchange can be turned to flashing yellow on the cross stree and flashing red to the left turn ramps, basically making it function as an unsignaled diamond. This arrangement saves driver time during low traffic hours. Not likely to be possible with this arrangement.

The only way this arrangement could make any sense at all is if the traffic interchange traffic between freeway and crossroad significantly exceed the through traffic on the crossroad.


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## George Harris

jis said:


> the_traveler said:
> 
> 
> 
> A good (?) example is Rhode Island and Massachusetts (right next to each other). In RI, the car already in the circle has the right of way and cars entering must yield to them, but in MA I understand it is the opposite (cars entering have the right of way).
> 
> 
> 
> If the Massachusetts law is as you say it is then the traffic engineers in Massachusetts should go and get their heads examined, or at least brush up on their flow control theory. That setup is inherently prone to create deadlocks.
Click to expand...

Unfortunately it is not the traffic engineers that make the laws iit is the gaggle of lawyers, lobbyists, and associated nincompoops that make of the state legislatures that make the traffic laws.


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## GG-1

George Harris said:


> jis said:
> 
> 
> 
> 
> 
> the_traveler said:
> 
> 
> 
> A good (?) example is Rhode Island and Massachusetts (right next to each other). In RI, the car already in the circle has the right of way and cars entering must yield to them, but in MA I understand it is the opposite (cars entering have the right of way).
> 
> 
> 
> If the Massachusetts law is as you say it is then the traffic engineers in Massachusetts should go and get their heads examined, or at least brush up on their flow control theory. That setup is inherently prone to create deadlocks.
> 
> Click to expand...
> 
> Unfortunately it is not the traffic engineers that make the laws iit is the gaggle of lawyers, lobbyists, and associated nincompoops that make of the state legislatures that make the traffic laws.
Click to expand...

Aloha George

How could you include "nincompoops" with Lawyers and Lobbyist. At least the nincompoop doesn't know any better while the others are for sale to the highest bidder. :lol:


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## George Harris

GG-1 said:


> How could you include "nincompoops" with Lawyers and Lobbyist. At least the nincompoop doesn't know any better while the others are for sale to the highest bidder. :lol:


To all nincompoops: My abject apologies for the insult.

George


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## MrFSS

George Harris said:


> GG-1 said:
> 
> 
> 
> How could you include "nincompoops" with Lawyers and Lobbyist. At least the nincompoop doesn't know any better while the others are for sale to the highest bidder. :lol:
> 
> 
> 
> To all nincompoops: My abject apologies for the insult.
> 
> George
Click to expand...

Thanks!


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