Two-Way Left-Turn Lanes (TWLTL) 1

[BruceHellmer]

Lee's Summit, MO has converted a 35-mph four-lane shoulder-less suburban road into three-lanes with a TWLTL and shoulders. Along this road, a residential intersection is separated from a Walmart entrance by only about 80 feet. Head-on left-turn traffic is competing for the short span of TWLTL between the intersection and the Walmart driveway. Many local residents are complaining about near-head-on collisions with the heavy Walmart traffic. Furthermore, This entrance is the only truck entrance for the Walmart Super Center and these trucks are also making this left turn. See attached Image from Google Maps.

Would it be safer to re-stripe with two through lanes and two left-turn lanes?

 

[IRstuff]

Google Map link, if anyone is interested:

https://www.google.com/maps/search/...MO/@38.9293622,-94.3649086,116m/data=!3m1!1e3

I would think that depends on what the traffic load is like. Why not extend the TWLTL into a left turn lane past the intersection on the left and stripe out a "Keep Clear" section at the intersection itself? Otherwise, wouldn't you have to lose the bike lanes?

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[BruceHellmer]

IRstuff:
Thanks for posting the Google Map link.

According to the city, those are not "bike lanes" but rather "paved shoulders". The city has not posted the shoulders for any use. While bicycles are welcome to ride on these "paved shoulders", they would not make a suitable "bike lanes" as they abruptly end short of Tudor Road to the North and short of Chipman Road to the South.

Swann Circle's traffic is minor, but Walmart's driveway is responsible for about half of all evening traffic on this stretch of Independence Avenue. Virtually all south-bound tractor-trailer traffic turns into Walmart's driveway.

North-bound traffic turning left onto Swann Circle frequently encounter head-on conflicts with south-bound Walmart traffic on this TWLTL.

To avoid confusion, lane striping is typically interrupted at intersections. Continued existence of the TWLTL through the intersections is implied.

 

[IRstuff]

Google Earth measurement suggests that getting 4 traffic lanes is not impossible, but the shoulders have to get shorted.

I get the lane striping bit; I was suggesting that the double-double yellow implied median be turned into an extension of the TWLTL, and that to keep the Swann Circle left turn clear, that the intersection be marked with "Keep Clear" or "Wait Here"

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[teeman]

I would consider extending the center lane lines to the edge of sidestreet to maximize storage and convert the center lane to back-to-back left turn lanes for this section. Minimal storage for the sidestreet and remaining pavement for the truck entrance.

 

[civilman72]

teeman: Two back-to-back left turns lanes will not work - the intersections are only 80' apart and Walmart delivery trucks are 50'-60' long.

Bruce: Was there a traffic study completed to get this re-striping approved? It would seem the entrance to Walmart should have been moved further north... Any other ideas why the shoulders were widened, maybe a high number of run-off-the-road accidents? It's sounds like it wasn't to accommodate pedestrian/bike traffic.

While I don't know the traffic volumes and distribution, it would seem to me it should go back to four lanes: the southbound traffic should have two thru lanes and northbound traffic has one-thru lane with a dedicated left-turn lane.

 

[BruceHellmer]

civilman72: I agree that there is not enough space between Swann Circle and Walmart's driveway for back-to-back left-turn-only lanes (LTOL)

As a consequence of this issue, I am no longer on cordial terms with the city engineer and will not attempt to speak for him. But he has stated unequivocally that there will not be more than one through lane in either direction. The city has been converting many low-speed (not exceeding 45 mph) 4-lane roads into 3-lane roads with a TWLTL and paved shoulders.

The following publication appears to be pertinent USDOT Road Diet Informational Guide. But, this publication warns:

3.3.7 Turning Volumes and Patterns

…

The operation of each corridor is unique and requires an evaluation to determine if a Road Diet cross-section conversion is
feasible. For example, if a major driveway exists along the corridor, it could change the potential impacts of a Road Diet by
introducing another (often closely-spaced) opportunity for additional vehicular turning movements. If motorists are trying to
turn into driveways opposite each other, opposite-direction vehicles could end up in the TWLTL and have potential conflicts.

Offset intersections can cause a similar problem, as vehicular left-turning traffic can enter the TWLTL from opposite directions,
desiring the same space from which to make their turn. Depending on the design of intersections and driveways, along with the
volume of left turning traffic, this can result in potential conflicts.


Walmart will not move its driveway to align with Swann Circle as this would interfere with their loading docks and automotive center.

I propose reverting back to 4-lanes for this short span, but with outer lanes for through traffic and inner lanes as left turn only.

What do you think?

 

[ACtrafficengr]

Side by side turn lanes may work here. Or, since Swan Circle loops back around to the main street, left turns into Swan could be prohibited at the north end.

The usual reason for 4-to-3 conversions is four lane undivided roads often have high crash rates. a 20-45% reduction in crashes can be expected after the conversion. Not bad for just moving some paint! (and signal detectors and heads and installing signs and ...)