Center Left Turn Lane 1

[TOHSEngineer]

I received a complaint about one of my town's center left turn lanes (both directions use the center lane for left turns). A homeowner has complained about almost getting into a head on collision with another motorist trying to make a left turn going westbound as the homeowner was traveling eastbound and also trying to make a left turn. The streets that the motorists were trying to turn left onto are approx. 500' apart. The road is a collector with a speed limit of 35mph.

Is this a problem that is fixable? Or is this just the downfall of the center left turn lane design. Any ideas/insight would be great. Thanks in advance.

 

[jgailla]

Add medians. They don't call them suicide lanes for nothing. Striping will help a little. If the roads they were turning on were 500' apart, they're both idiots.

 

[kellig]

I would try striping first. Add some arrows to your TWLTL if they are not already present; the MUTCD has guidelines for placement. Medians are expensive and limiting access will be unpopular with the public.

 

[Drumchaser]

I concur with kelli

We have installed medians in several "suicide lane" areas, and suffered much abuse about the access loss to/from local businesses.

Who cares that the medians have substantially decreased accidents.

Striping a gore area with hash marks and 8" channel line should help. The prob with our TWLTL's was the folks using it as an accelleration lane (illegal) as well as the "head bumpers" you referred to.

 

[Debaser]

(UK perspective)

Wow! 500 feet is approximately 150m, that's a long distance to be travelling in a 'ghost-island' turning lane wanting to turn right (or left, in the colonies). (I am assuming that this is a 'left-right' staggered juntion)

We allow a distance of 50m back from the centreline of the minor road to enter and decelerate from a design speed of 70kph (equivalent to 40mph). From a safety point of view we'd look to allow the continuous ghost-island so there's no unneccessary widening and narrowing of the running lanes, but separate the two turning areas with hatching (striping?) and use bifurcation and direction arrows to direct turning traffic to the lane they have to use, only when they need to.

Worst case, in a built-up residential area, we may use a pedestrian refuge with bollards to identify its presence to separate the two turns.

 

[ACtrafficengr]

Ah, yes, short memories. Two-way left turn lanes are not suicide lanes and should not be described by that term. 2WLTLs (pronounced 'twittles') have been shown in many instances to reduce the number of crashes, compared to undivided roads. They aren't as good for that as physical medians, but a measure that reduces crashes should not be called a suicide lane.

The true suicide lanes have been banned for decades. I want to say since the 1948 or 1954 MUTCD, but I'm not sure. They were center lanes that could be used for passing in either direction, resulting in high speed head on crashes. Head ons in 2wltls tend to be low speed.

One way to discourage abuse of the 2wltl to get to the intersection left turn bay is to stripe a flush median taper between the 2wltl and the turn bay. Sure, people can and do drive over the cross hatching, but at least they know they aren't supposed to, and are a little more cautions. A disadvantage to this is if the turn bay isn't long enough, drivers will sometimes block the through lane rather than store on the flush median.

"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

"I'm searching for the questions, so my answers will make sense." - Stephen Brust

 

[teeman]

The conflict is an unfortunate side effect of the distance between intersections. At 35mph (51 ft/s) it would take approximately 5s to come to a stop at the comfortable rate of 10 ft/s/s. The distance traversed during that time is approximately 380 ft, more than half the distance between intersections.

Technically, the vehicle in the TWLTL first had the right-of way. The second vehicle should have adjusted its speed to compensate and waited for vehicle 1 to pass to before entering the lane.

That said, I can recall seeing an elderly driver travel in a TWLTL for almost a quarter mile before turning.

 

[TrafficDesigner]

I agree with ACTrafficengr. I can't imagine how they would have almost had a head on collision between two intersections 500' apart, on a collector street at 35 mph. I suspect someone or maybe two someone's were driving in the center left turn lane longer than they should have been.

A median on a collector street seems a little extreme and too expensive just for the sake of "separating the children" I would use a painted median first if it were really neccessary. Alternatively if it is really a problem for these two streets you could try a 100' left turn only queue length with a 100' taper in front of each of them and still have a 100' painted median between them or at least solid double yellows.

 

[teeman]

The concept of converting the TWLTL into back-to-back left turn lanes does have merit, but a number of questions need to be asked:

Is the conflict being addressed a recurring conflict or just an isolated occurance?
Does the TWLTL service any properties between the side streets or does it actually operate as a B2BLTL?
Can you provide left turn storage to accommodate the left turn demand?

Every location has its own unique characteristics. One urban corridor in our area has a TWLTL with very short storage lanes at some intersectiions. At others, the separation between sidestreets is so minimal it wasn't possible to provide single direction left turn lanes.