DDI Diverging Diamond Interchange

[ksa8907]

Same effect, no stop lights.

http://www.carmel.in.gov/modules/sho...px?imageid=720

[acparker]

Traffic circles are great in light traffic, but heavy traffic becomes a nightmare.

[Zach]

We have a couple of these Split Diamond Interchanges now near me. I agree with Charlie with having to potentially sit and wait at red lights for a while though.

NCDOT: I-485 Charlotte Outer Loop

[ksa8907]

Originally Posted by acparker

Traffic circles are great in light traffic, but heavy traffic becomes a nightmare.

Define heavy? You don't take a main thoroughfare through a roundabout, just the traffic that is merging on/off. You use traditional exits that go into traffic circles instead of stop lights.

Those traffic circles are in one of the most highly traveled area of indiana.

[acparker]

I checked out the

youtube

of the simulation. In heavy traffic, the roundabout will be full and approaching traffic will back up, waiting for an opening. In this case, with two lanes in the roundabout, it doesn't matter which lane has a vehicle in it, the approaching vehicles must assume any vehicle in the roundabout will veer to the right and therefore must wait until it passes.

Again, in light traffic, roundabouts work great., but in heavy traffic you get gridlock.

[Fat Charlie]

Originally Posted by acparker

Again, in light traffic, roundabouts work great., but in heavy traffic you get gridlock.

Cars already in the circle are only part 1. Cars stopped in the left lane waiting to enter the circle have to watch over their right shoulders at the same time for jerks sailing down the right lane and popping into the circle at the last moment, just as the lead car in the left lane tries to enter.

Driving a tiny, underpowered car, I'm almost as big a mark as truckers. But I've got a manual transmission and an attitude, and those jerks need a hell of a speed advantage to keep me from putting them in the grass. It happens a lot more than it should- I've had two in the last month. 10% of the time is pathetic. One came to a dead stop to avoid being put on the grass and the other got stopped by the state trooper who was watching the area, whose attention I got by laying on the horn as I launched.

[acparker]

Any interchange where I live is a major thoroughfare. Interchanges are too expensive to waste on lightly traveled roads.

As to what constitutes heavy traffic, I suppose it is relative. I live in a highly built up area of about 2 million people. While Salt Lake and the Wasatch Front are similar in population to the Indianapolis metropolitan area, we are squeezed by mountains, the Great Salt Lake and Utah Lake, into a narrow corridor. Add in an almost pathological disregard for planning and that leaves us with horrendous rush hours.

UDOT has been very aggressive in testing innovative solutions to traffic flow. The Detroit left turn is probably the worst and it has only been used in a couple of spots that I have found so far. They tried the Displaced Left-Turn Intersection (also called the Mexican left turn because it was first used in Mexico City.) about 15 years ago and have become quite fond of it.

It takes some getting used to and it is very frustrating when you forget to get in the turn lane. They time the lights well so there is no wait after the first light turns green, unless you floor it.

Roundabouts are found in slower, lightly used secondary roads and they usually work quite well.

There is a roundabout in my wife's city, Guayaquil, Ecuador. It is at a bottleneck and was a major nightmare, and that was before the traffic got really bad after they dropped the heavy tariff on automobiles back in the 90's. They have since built around it, though I don't know how the improvements have fared through the earthquakes the past couple of months.

[jamesqf]

Originally Posted by ksa8907

Define heavy? You don't take a main thoroughfare through a roundabout, just the traffic that is merging on/off.

Wish you could explain that to the Nevada DOT :-(