Modern Vespa

A slightly hijacked discussion on another post about roundabouts reminded me of this relatively new (to the Midwest anyway) displaced left turn intersection idea. It is also call a continuous flow intersection.

I read a ScienceDirect paper that did a comparison of the stats of a DLT intersection compared to a traditional intersection and while it concluded that it did increase traffic flow it also showed an increase in certain crash types including injury crashes. Caveat is they didn't have time rich data and only had a handful of DLT intersections to use.

Would like to see a comparison to roundabouts as I don't think DLT's would compare well to them. Seems to be just a more expensive way to marginally increase flow without significant safety increases and simultaneously avoiding the battle for roundabout installations . What do y'all think?

I can see the left turn banking up across the left lanes during heavy traffic. not so good.

Also anything new is going to have a learning curve.

Personally I like the roundabouts, in my neck of the woods, at four way stop signs there seems to be one direction that has the majority of traffic but roundabouts aren't the perfect solution as many people get confused which lane to enter into them when there are multiple lanes, some outside lanes exit before the exit they want and the inside lanes sometimes lock them in before their exit, unless they cut someone off last second.

Here's one in Irvine CA that I take often, you hardly ever have to stop if you're going up or down Laguna Canyon Rd

I see wrong way drivers headlights coming straight at me😱

I fail to see how this is an improvement over a roundabout, or even a traditional intersection. It requires more space than a regular intersection, more signal synchronization than an intersection or a roundabout, and is neither simple nor elegant.

FFS, just build a roundabout!

I don't know how this is supposed to move more traffic, when right turns on red are no longer possible?
DLT will confuse tourists & drunks, encouraging them to drive on the wrong side of the road

Here in Reno we have left turn arrows that flash yellow after both directions are green, wee! confuses the shyt out of everyone
The preferred method is to pull out into the intersection far enough for 2 cars, so when the main light goes red we can both turn

The local red light protocol is if you are within 5 car length when the light goes from yellow to red, keep going!

Unless I see more data to suggest otherwise, which I don't anticipate will exist, I agree.

I have one of these a couple miles away from my house that opened a few years ago. There is a learning curve and folks unfamiliar with this tend to cause issues (either tie ups or accidents).

The lights are synchronized so that those turning left have already crossed over the oncoming lanes to the left turn lanes before the oncoming traffic is released. The benefit here is that everyone turning left or going straight is released at the sametime, crossing over or turning left onto another main road, thus relieving the backups that occur sometimes with heavy left hand turning traffic. The DLT lanes are controlled by lights that stop traffic when the oncoming traffic is released.

In this pic, only the east and west bound traffic has the DLT option. It works reasonably well for those with familiarity. But it requires careful synchronization of traffic lights. If the lights lose power, it will be total anarchy.

For those interested in seeing this in person, take exit 41 off I-75 - south of Dayton Ohio and head east on Austin Blvd. Great Pizza at Dewey's in the Austin Landing Shopping complex.

Roundabouts work with no signal synchronization, in fact no signals at all. They function perfectly even with no power.

You're absolutely correct, Jess - but one reason roundabouts are not as common as they deserve to be is that their failure mode is so bad, and pretty frequent. A handful of roundabouts exist in the NYC area - so few that I would guess most experienced area drivers have never seen one of them - and there are fender-benders and smashups in them all the time. Entitled drivers with limited experience don't understand that vehicles in the roundabout have the right of way, and blithely ignore yield signs on the regular even in the best of circumstances.

I don't like using those roundabounts when I'm on two wheels.

https://maps.app.goo.gl/yJKFzpyDr52jLBeZ8

Of the two in the area where you centered the map -- Bartow Circle and City Island Circle -- one of them appears to be a roundabout and the other appears to be a traffic circle, with stop signs.

Traffic circles predate roundabouts and are widely considered to be inferior to the modern roundabout. Importantly, modern roundabouts do not have stop signs. I've ridden through hundreds of them in Italy and I think they're great.

hmmm....now where have I seen these before...

I'm agreeing with you. I suspect all traffic designers do too. But they require a high degree of cultural familiarity and etiquette to navigate correctly. In other words they have to be common in order for their use to be common knowledge.

That is, or would be, extremely expensive to retrofit in US urban areas where real estate is expensive and public will is fickle.

And where they aren't common knowledge, they result in a lot of collisions, which is exactly what happens in those two traffic devices, with or without the plethora of stop signs, yield signs, triangle signs painted on the road, and traffic police monitoring on weekends. I consider them dangerous on two wheels.

Sadly the roundabouts in fuckin Brooklyn have signals to enter and exit them. I always thought roundabouts were meant to allow smooth flow of traffic without dealing with traffic signals. Id say even with signals etc, NYC has become worse since the pandemic with regards to rules being followed while riding.

That's not a roundabout. That's a traffic circle, which was invented in America about 120 years ago by well-meaning people who got it wrong.

The UK revisited the concept in the 1960s and managed to get it right.

Around here, the two car rule was widely followed until somewhat recently. Now it's often three or even four cars.

The state of MA is odd as it has had roundabouts for a long time before they were cool. They call them rotaries but they function exactly like roundabouts. For the most part they work well but one of the rotaries called Grant Circle is at the end of rt. 128. People come into it coming down a long hill at hwy. speeds and a number of them refuse to slow and yield to traffic on the rotary despite various warnings.

Also, people tend to stay on the outside lane even if they are going halfway, 3/4 way or doing a U-turn making people avoid the inside lane for these turns to prevent getting trapped. There have been some decent wrecks there as well as many road rage instances.

The odd thing is the City has been wrestling with this issue for decades since I was a kid living there. Looking at it from google maps I am pretty sure I can see at least three things that could be done to fix it. One involves putting in traffic "calming" measures like speed bumps on the entrance from the main highway (where the 18 wheeler is in the pic.)

That is the problem with multi-lane roundabouts. People enter in one lane and leave in another. Somewhere in the middle, there is conflict.
I don't like them, but I grok one-lane roundabouts, they slow traffic and at the same time keep it moving. But if you find yourself on Hwy 179 heading to Sedona on a weekend, you will curse the name of the bastard who ever thought the thought.

Roundabouts should never be installed if there's the possibility that any of the exits might get blocked by heavy traffic. That's one of the other rules with roundabouts, never enter unless your exit is clear. They got that totally wrong in Sedona, I cursed them too the one time I drove through it.

they recently ruined a local t-intersection by closing a lane and replacing with a dedicated bike lane.

it was essentially a t-intersection outside a shopping centre. single lane street that split into dedicated left and dedicated right turn lanes 50m before the intersection. left turn was usually fast flowing and right turn was always slow. now a single right hand turning car blocks al those fast left turns resulting in traffic queued way way way back up the street - twice as far as it used to.

"but we made it safer for cyclists" and pissed off all the cars and and angry drivers do stupid things. doh.

Once you realize that the people in charge can actually find a reason not to replace what is arguably the worst intersection in the "civilized" world, a giant six-way stop-sign-controlled fiasco, with a roundabout, it will occur to you that we are up against something unknowable.

https://patch.com/california/beverlyhills/beverly-hills-rejects-plan-roundabout-6-way-intersection

we've got a 6 way intersection not to far from me WITH MULTIPLE TRAM LINES. admittedly it has traffic lights not just stop signs. Of course the trams have their own lights ...

https://www.google.com/maps/@-37.8314576,145.0566885,18.94z

Like going out and buying a bicycle?

The one in BH is a busy six-way stop sign with no lights or circular motion, even though it's basically a circle. It makes no sense.

More like cutting off the lycra warriors

Outside Atlantic City near the airport is a 5 way intersection that was converted from a circle to some poorly designed engineer's version of a Clusterf*&k. How in hell did they ever come up with such a stupid plan. Anytime one of the roads has moderately heavy traffic, the whole thing goes into a stall. You can't get in and you can't get out of it.

Ireland had many circles and they all seemed to work just fine. Maybe they have better engineers?

What I've noticed about roundabouts is that they work for a two-wheeler pretty well when car drivers follow the local rules and the possibilities for lane changes within the roundabout are kept minimum.

All the 'close calls' to me have happened when a car has either changed lanes within a roundabout and not seen me, or a car driver has ignored the local rules how the lanes should be used...e.g. took an exit directly from an inner lane and cut me off.

As a car driver, I'll have to say that sideways visibility especially in smallish roundabouts is poor. Very easy to loose a car somewhere outside the scope of mirrors, much easier to miss a bike

All in all, I do like well designed roundabouts, preferably with drivers who follow the rules We do have lots of small 1 and 2 lane roundabouts.

The best way I've ever seen to lessen traffic congestion was the gas crisis. It created a thing called ride share.
Twenty years ago about 4 miles from my house they built a Park and Ride. For some reason It's parking lot is always empty

COVID lockdown was pretty effective too.

So was Thanos.

https://xkcd.com/2842/