PA's first diverging diamond interchange finished

ConstructionDIVE ^ | August 24, 2017 | Kim Slowey

[HereInTheHeartland]

Well it actually contributed in most people’s opinion.
Driving on its very easy to see how it might have happened

[TXnMA]

...or tried to cross the Cape Cod Canal on a holiday weekend...

[lewislynn]

•The DDI design eliminates left turns across oncoming traffic, improving vehicle flow and decreasing the chance of accidents.

AKA a freeway...been around since at least the fifties.

[central_va]

Whats wrong with the classic clover leaf?

[Vision Thing]

Ok, here goes. Time for me to geek out on this.

Compared to the ddi design, the clover leaf requires a 270-degree turn for a northbound driver who wants to turn onto the westbound street. The ddi makes such a driver only do a 90-degree turn.

Also, in the same scenario, the clover leaf requires the driver to slow down much more than the ddi driver, thus it’s a bigger drag on fuel efficiency.

Also, in the same scenario, the clover leaf driver has a really bad view of the traffic on the lane into which he is megring. The ddi driver is able to see his merging traffic to his rightside. So it’s much safer.

One other disadvantage the clover leaf has is it’s requirement for more real estate.

After all that said, the clover leaf has the distinct advantage of requiring no stoplights.

#CivilEngineeringIsBetterThanCivilWar

[P.O.E.]

Diverging Diamond Interchange Visualization

[RegulatorCountry]

... but a cloverleaf is fun when you’re young, dumb and willing to do stupid stuff just to amuse your friends. Ever done a full cloverleaf? Around and down, up and around, around and down, up and around again, then on your merry way? I have.

[Vision Thing]

Lol! I am gonna try that.

Speaking about having fun with cloverleaf intersections,
I once got stuck behind a chicano lowrider who slowed down when entering a 270-degree cloverleaf turn. He then sped up to about 50 mph and made the turn with no problem at all, even when the turn had a speed limit of 25 mph.

Those low riders have no fear of toppling over, unless of course the rightside hydraulics accidentally turn on.

[itsahoot]

Whats wrong with the classic clover leaf? Hey I was happy with 4 way stops and a 2 lane Highyway 66

[Ronaldus Magnus]

Diverging Diamond Interchanges necessitate the use of multiple stoplights. This is a major disadvantage over cover leaf type interchanges and makes them far more wasteful of time and fuel. I would much prefer a 270 degree turn than waiting at multiple stoplights.

[Vision Thing]

Yes, the cloverleaf’s biggest selling point is that it requires no stoplights.

As for the ddi, it looks like each direction of a ddi street only has two stoplights: one to enter and one to exit.

The ddi designer said that one of his design goals was to prevent multiple redlights for those entering a ddi. In other words, if you are unlucky enough to get stopped at a red light entering a ddi, once it goes green, you won’t get a red light at at the other end.

[hal ogen]

All highway engineers must have gone to the same seminar. We have one of those here in St George UT crossing over I15.

[Lurker]

It’s right at Route 59 and I-88. It does work well.

L

[Daffynition]

Looks like someone in the DOT politicized religion.

[mountn man]

I’ve gotten hung up at the west bound exit of 59 a number of times, at rush hour, trying to head south.

Things are A LOT smoother and faster now.

Was a little disconcerting the first few times I went through it though. The traffic pattern did make me feel like things were a little backwards.

[mountn man]

Whats wrong with the classic clover leaf?

Half of the exiting traffic will not stop, or seldom stop, depending on traffic congestion on the arterial street. Thus relieving congestion at the off ramp.

Next, on the arterial street, when a person goes to enter the on ramp, it's a straight access, with no traffic to cross over. You just make your turn onto the on ramp and merge with traffic also entering, coming from the opposite direction. No traffic signals stopping you or limiting your time to turn. Thus, less congestion.

The only traffic signals are at the left hand turn, off ramps and the 2 arterial road cross overs.

Generally, the crossovers are set, that both crossovers, in the same direction, are green at the same time, allowing traffic to continue through both lights, clearing the entire intersection...as long as traffic on the arterial is moving fairly well.

It REALLY IS an improvement.

[Tolerance Sucks Rocks]

OK, it was I-86 and US 91 — I got the interstate no. wrong, but I did drive through that intersection.