March 9


Removing a Left Turn Lane to Provide for a Bike Lane

By Mike Spack

March 9, 2017

bicycle traffic, bike lane, Case study, Intersection, Left turn lane, LTL, Multimodal traffic

Bicyclist. It is a word that can incite frustration in the minds of both drivers and traffic engineers alike. But, let’s face it: bicycles are good for the environment, they are cost-effective, they are good for our collective and individual health, and the presence of cyclists within a community creates a positive image that says we care about the environment, we are health-aware, and we feel safe enough in the community to ride our bikes down these city streets.  With an increasing number studies showing that bicycle traffic increases in areas that have dedicated infrastructure in place for cyclists, it’s no wonder why we are starting to see an increase in requests for multimodal traffic solutions.

Case Study: Louisiana Ave. & 28th St., St. Louis Park, MN

The City of St. Louis Park, Minnesota has been very diligent in reviewing their infrastructure and ensuring their transportation planning process is keeping up with the growing needs of the community. Over the past 10 years, we have worked with them on many projects, particularly as they have started to focus on multimodal traffic solutions. Most recently, they asked us to look at the intersection of Louisiana Ave. and 28th St. to see if removing the left turn lane on 28th St. would be a viable option to provide space for a bike lane. (This case study was a featured webinar for Traffic Corner Tuesday. Check out the recording)

Louisiana Ave. is a minor arterial, two-way road that carries roughly 17,200 vehicles per day, whereas 28th Street is a neighborhood collector carrying 2,900 vehicles per day. The city was considering 28th Street into a bicycling corridor.

Step 1: Consider Options

Our first course of action, before getting to deep into the analysis of the site, was to put pencil to paper and sketch out some options.

Our first option was to reduce the lane width to 10.5’ lanes in each direction on 28th St., add a 5.0’ bike lane, and a 7.0’ parking lane. We recognize that a 10.5’ lane has the potential to get tight, but we felt comfortable with this option because – apart from the occasional school bus and garbage truck – there are not a lot of large vehicles traveling on this road.

Our second option was to create a bike lane on either side of the road, and we used variable lane widths to determine that it would be feasible to have two 5.5-6.0’ bike lanes with two 10.5-11.0’ drive lanes on this street.

The final option was to eliminate the variable space from option 2 to create delineators for the protection of the cyclists. Studies have shown that bicycle traffic increases and related injuries decrease when there are protected lanes for cyclists to travel in. Unfortunately, this option creates a challenge during the winter months, as snow removal becomes a necessary consideration, but that is certainly not a deal-breaker for this scenario.

Step 2: Analysis

After sketching out three viable options for creating bike lanes on 28th St., was to run analysis using Vistro.

Using the existing timing, turn movement and volumes to determine that the intersection was operating at Level of Service D. When we factored in an increase in bicycle traffic, taking out the left turn lane and some timing adjustments, we found the Level of Service would stay roughly the same.

When we looked at queuing, however, we saw some red flags that were cause for concern. By forcing the right turns to mix with the left turns, we saw a 2x-3x increase in our 50th percentile queue.  With only 260 feet of roadway before the intersection to work with, the increase in queue was a considerable concern for us.


While we are typically very open to repurposing space and pushing the boundaries in an effort to keep traffic solutions current and accommodate multimodality, the increase in queue and the safety implications were just too significant for us to ignore.

We have provided the city with our findings, and they are currently exploring ways to validate the findings via temporary trials. As we all know, software and modelling can be excellent tools for analysis, but experiments can provide us with real data that we just can’t get in any other way. We look forward to seeing the results of these experiments and will keep you posted!

Are you interested in learning more about bike lanes? Check out our free Traffic Corner Tuesday webinar Removing a Left Turn Lane to Provide a Bike Lane.  In this episode, Mike Spack and Bryant Ficek walk through the case study that was basis for this article.

Or signup for our Traffic Corner Tuesday webinar series. Each webinar is 30-minutes of free traffic engineering best practices from industry experts.

  • I like how you’ve “pulled back the covers” to explain the methodology in detail — nice write-up on this, particularly for those who might be unfamiliar with how one does this.

    I know it would be quite a bit more complicated, but I would assume you would apply essentially the same methodology for any geometry change to a series of intersections, such as if you were implementing a light-rail corridor down a median that would require the elimination of certain conflicting turn movements; it would just be that you would need to study a larger set of intersections, and the changes would be more complicated to document, perhaps being done on a spreadsheet diagram rather than by hand on paper. Could you comment on if the methodology stays the same?

  • The capacity analyses/methodology would stay the same. With any type of improvement analysis, concepts are often laid out with hand drawing when you’re at the early feasibility stage. Even this plan would move into CAD drafting for final design.

    – Mike Spack, PE, PTOE

  • Gentlemen:

    I have a few comments:
    1) An ADT of 2,900 is very low, so why are bike lanes needed? If they are not, consider creating a bike boulevard or neighborhood greenway.
    2) The left turn lane issue should not drive the final configuration choice of the entire corridor. If left turn lanes are needed you may taper out the bike lanes on the approaches to the signalized intersection and reestablish them downstream of the signal. On a street with such a low ADT, this should be quite easy for motorists and cyclists to navigate. I’ve done this on much busier streets. It has the benefit of eliminating right-hook crash threats at the signal – where you would expect the heaviest right turn volumes.
    3) If you retain the EB left turn lane, install one on the WB approach to improve sight lines for drivers and cyclists turning left. It will eliminate the negative offset.
    4) The left turn lane(s) don’t benefit only motorists. Cyclists waiting to turn left will use them. They will prefer to make a left turn from a left turn lane vs. a shared thru-left.
    5) Please avoid the 7′ parking lane / 5′ bike lane scenario. The bike lanes will be almost completely within the door zone. This is hazardous for cyclists. If parking must be retained, the bike lane should be eliminated. Yes; it meets AASHTO minimums, but it’s still an awful layout for cyclists. Experienced cyclists would avoid using the bike lane and would use lane control in the adjacent general purpose lane. It’s the newbies who won’t know any better and will ride within the hazardous door zone.
    6) If you do install bike lanes avoid any design that includes delineator posts / pylons on this street. They offer no protection to cyclists and they will interfere with motorists trying to merge into the bike lane on the approach to a right turn. In every state except Oregon, right turns are to be executed from the right hand lane whether it’s a general purpose lane or a preferential use lane like a bus lane or bike lane.
    7) If pylons are in place, motorists may be forced to turn right from lane #2 (the lane to the left of the bike lane). This is incredibly dangerous for cyclists and has resulted in numerous fatalities. This is especially dangerous on long flat grades or descents where cyclists can travel at or close the speeds of motorized traffic. This street has numerous access points where cyclists would be vulnerable to the very dangerous right hook. Generally speaking, it’s a very bad idea to force motorized vehicles to turn across a bike lane instead of allowing them to merge into it before turning.
    8) Consider adding an EB leading protected-permitted left turn if the left turn lane is eliminated. As you mentioned it will clear the first few vehicles in the queue before WB traffic is released.
    9) Note that the overall benefit to all users likely is with the retention of the EB left turn lane and the addition of a WB left turn lane. Eliminating the EB left turn lane allows for the extension of the bike lanes to the signal (with marginal value), but it negatively affects motorists and cyclists making left turns.
    10) Examine the possibility of shortening the eastern (NB side) parking lane on Louisiana Ave. There’s enough pavement to create a short NB right turn lane – which will move some of right-turners out of the NB through lane queue.
    11) You may also be able to slightly extend the NB left turn lane with a minor restriping project.
    12) If you do provide bike lane, consider 10′ general purpose lanes and 6.5′ bike lanes. The extra six inches is more valuable to a cyclist than a motorist. Again, the ADT is crazy low. Our expectation of two trucks passing would be even lower.
    13) I would ask the city to consider keeping the EB left turn lane, and adding a WB left turn lane. The bike lane vs. bike boulevard / greenway decision is an independent matter.
    14) If a greenway is selected, add a striped parking lane on the northern side of the street to calm traffic and provide a buffer for pedestrians using the sidewalk.
    15) If bike lanes are selected, provide the left turn lanes and taper out the bike lanes on the approaches to the intersection. And, no matter what, avoid creating the illusion of protection by installing pylons. Along this corridor they merely would channelize cyclists up to the conflict zone (coffin corner) at each access point.

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    Mike Spack

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