oos E-Newsletter #281: Members Share Thoughts on Emerging Transportation Designs


In last week’s newsletter () we discussed several emerging, “alternative” interchange and intersection designs: the Diverging Diamond Interchange, the Displaced Left Turn Intersection and the U-Turn Intersection. We asked if you’ve ever driven one and what you thought about them overall. Here are a few of your responses.

From Anatoly Arutunoff, Oklahoma

If people follow the signs—good signs—the designs will work. There’ve been vaguely similar setups in Italian and French cities for decades: You peel off right onto a parallel road through a divider (into the lane where the curb parking is) and go down a ways to turn left at a minor intersection (sometimes a one-way street going left) to then cross your previous main artery to complete the left turn.

From Fred Suess, Arizona

These new innovations seem well thought-out and could work well. I’d like to see them in use. As you remark, some driver education will be necessary. In the UK, roundabouts are everywhere, small roads and large ones. The public seems to have no problem, only some training, and safer roads are the result.

My first thought is of the impaired driver—in Colorado and Washington, where cannabis is legal and in many cities there are some drivers using alcohol, perhaps all day long. Their responses to these new circumstances could be some confusion, even given training.

From Don Bain, Washington

Looking at this diamond design it’s obvious it will have a great slowing effect on traffic due to two lights in close proximity and crossing lanes. Of course, the signals’ timing will be set vis-à-vis the posted limit rather than what people really drive at, causing more congestion. I’d like to see long-term stats on accidents and congestion inducement before subscribing to such innovative designs. What appears nice on paper is often not nice when a wide range of vehicles and human beings try to use it.

From Mark Hammond, Utah

I do not mind these intersections at all, and I’ve navigated all three of the types you discuss. (I’ve actually been through the 5400 South and Redwood intersection shown in your diagram.) The key is that the signage is good and local drivers are well educated about them.

From a New York Member

This crossover business scares the dickens out of me. It will take me some time to figure it out while in danger of being run over. Some people may never figure it out, causing substantial accidents.

Since the installation of a couple of roundabouts in our area it is almost impossible to get out of some businesses and onto the highway due to the unrelenting stream of traffic. With a traffic light periodic lulls in traffic would permit egress. A small roundabout in our area cost a quarter of a million dollars to construct. That would pay for the old traffic light operation and maintenance for a long time. The construction costs provide plenty of money for political campaign kickbacks.

I’ve studied the diagrams you posted and will probably go to great lengths to avoid such places because of lack of confidence in both myself and others to safely navigate them. Traffic patterns to be safe should be intuitive, not a set of mental gymnastics which have to be learned and mastered.

From Jim Walker, Michigan

I have driven DDIs of the first design and they work very well. I have not driven the second type. The third is indeed the Michigan left, and has been used very successfully here for a long time. It is used with a lot of four- to eight-lane major roads to completely eliminate the left turns across traffic. It does take a slightly longer time for the turning vehicle but also significantly lengthens the percentage of available green time for the major road because you don’t need them to stop to allow the lefts. It works the best where there already was a median or when the road is re-designed that way during reconstruction.

From Wallace Phillips, Ohio

There are several Restricted Crossing U-Turn or RCUTs on a road called “Ohio Bypass 4” in Hamilton OH. There is a traffic signal at the U-turn. I used to wait through five light cycles but now I never wait more than one. The only problem is, since there are two lanes turning left, people tend to drift out of their lane unintentionally and cause accidents. You have to watch out for those.

Not an oos Member yet?

Join today and get these great benefits!