It’s Not a Bottleneck, It’s a Turkey Neck

Around these parts, it’s not an unpopular belief that the Hennepin-Lyndale Bottleneck is a bit – ah, how to put it? – oversized. The City of Minneapolis’ Public Works Department does not appear to share this belief, as they’ve submitted a design for the Bottleneck that retains its massivity. When a loved one has a weight problem and he or she doesn’t want to admit it, Dr. Oz might recommend using the neutrality of facts to make a case. So can we use numbers to determine whether there are too many lanes in the Bottleneck?

I ran the numbers; click to jump to the results or read on for a detailed explanation of how I got them.

Do we really need more lanes above than below? (image: Wikimedia)

Do we really need more lanes above than below? (image: Wikimedia)

When it comes to numbers, few are more well-regarded at the moment than wunderkind Nate Silver, so I’ve copped the methodology used on recently on his 538 website to explore whether bike lanes cause congestion. Authors Gretchen Johnson and Aaron Johnson used MnDot traffic estimates as a base, then assumed based on an FHWA manual that 10% of their daily estimates used the roadway in a typical peak hour. Finally they assumed that lanes can handle 1,000 cars per hour based on info they claim to have gotten from the Transportation Research Board’s Highway Capacity Manual, which we can’t verify without paying despite the taxpayer funding that went into this product.

The 1,000 cars per hour rate is probably too low because it likely is based on the capacity of roadways meant for much higher speeds than the 30mph-posted Bottleneck. Since cars need more space to move faster, the lane capacity of lower-speed roadways would logically be higher. In fact, there is research that suggests that the lane capacity of urban street lanes is more like 1,600 cars per hour, and this signal timing course from the University of Idaho suggests using 1,900 cars per hour as a base number and adjusting downward to account for squeezes like high turn volumes, lots of trucks or buses, or lots of pedestrians or bikes.

We know that there are a lot of things that squeeze the capacity of the bottleneck, but it’s beyond the scope of this post to thoroughly study these factors (that’s Ole Mersinger’s job). So I split the difference between the figure from 538 and the base rate from the University of Idaho, and assumed that each lane in the Bottleneck can handle a maximum of 1,450 cars per hour. I bumped that number up against traffic counts from the City and did all the 538 mathy stuff to figure out what percent of that maximum theoretical capacity is being used in the different segments of the Bottleneck, and how much would be used if those segments were reduced by one lane. Here’s what I found:

First, here is the capacity of the existing facility:

BottleneckLaneCapacity

Now the capacity if a lane were removed from the segments that currently have multiple lanes:

BottleneckLaneCapacityMinusOneLane

Here’s a summary table, with the segments that could handle a lane reduction without risking more than moderate congestion highlighted in yellow:

BottleneckCapacitySummaryTable

So it seems that the majority of the Bottleneck and almost all of what is currently under consideration for reconstruction could be reduced by at least one lane without exceeding capacity. This may not seem to match your experience, since traveling through the Bottleneck feels like battling a hydra with red lights for eyes and tailpipes for necks. But if you pay attention to the clock, you’ll typically find that it takes less time to travel through the three-quarters mile of Bottleneck (from Dunwoody to Franklin) than it does to travel a comparable distance in Uptown or Whittier along Hennepin, Lyndale, or Nicollet. The Bottleneck is an urban street; why should there be an expectation that it be any faster than any other urban street?

Rumor has it that suburban political interests will not allow for the Bottleneck to be rebuilt with fewer lanes than are there right now. Meanwhile a grassroots coalition has called for the prioritization of the long-neglected aesthetics of the space, and for bike, pedestrian, and transit transportation to come before personal car and truck traffic. A revised design for the reconstruction will be released at a public meeting on August 4th, show up and see which side won out.


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10 Responses to It’s Not a Bottleneck, It’s a Turkey Neck

  1. Bill Lindeke
    Bill Lindeke July 17, 2014 at 3:34 pm #

    We need to spread these rumors. Which suburban political interests!? Are we talking Hennepin County Commissioners?

  2. Walker Angell
    Walker Angell July 17, 2014 at 3:47 pm #

    Great stuff. I wonder how many of the cars driving through there every hour are making trips of less than 2 or 3 or 5 miles one-way? What if 50% of those trips were replaced by bicycles?

  3. Obvious Oscar July 17, 2014 at 4:17 pm #

    I’m all for a better rebuild of the Bottleneck but let’s not conjure up the soon-to-be-passé boogeyman of “suburban political interests.” If current cultural and development trends continue, in a few years “suburban political interests” will simply be code for “poor people.” Also the way you deploy it here (“rumor has it”) only made suspicious about why you’d opt to be so blatantly sketchy in your writing.

    • Alex Bauman
      Alex Bauman July 18, 2014 at 11:14 pm #

      I happen to think that urban vs suburban is the fundamental dichotomy of American cities, even more so than black vs white. And I don’t define urban vs suburban by municipal boundaries, and I highly doubt it’s going away anytime soon. If you are curious about this rumor, why don’t you do some research and write an article about it? I bet if you ask CM Lisa Goodman or Met Council Transportation Committee chair Adam Duininck about it, they’d have some interesting things to say.

  4. Froggie July 17, 2014 at 7:44 pm #

    Careful. A lane’s capacity per hour in an urban area is highly dependent on green time.

    BTW, I have the 2000 Highway Capacity Manual if you’d like me to do some number crunching.

    • Alex Bauman
      Alex Bauman July 18, 2014 at 11:07 pm #

      If my memory serves me, the green time in the Bottleneck is skewed towards traffic traveling through the bottleneck. But yes, doing a full intersection analysis is more complicated, which is why people get paid actual dollars to do it. Unfortunately, they are also paid to build roads, not not build roads.

      If you want to look up the Saturation Flow Rate for urban arterials in the Highway Capacity Manual and reproduce their methodology here, that’d be cool.

  5. Stacy July 18, 2014 at 9:27 am #

    “Finally they assumed that lanes can handle 1,000 cars per hour based on info they claim to have gotten from the Transportation Research Board’s Highway Capacity Manual, which we can’t verify without paying despite the taxpayer funding that went into this product.”

    Sounds like paranoia. Specifically “info they claim to have gotten.” Do you mean to imply that the county engineers are lying to your face? That they just made up the numbers?

    If you have a good argument, use it. Don’t call people liars without any sort of evidence. Posts with this kind of shadowy language bring down the credibility of street.mn.

    Aren’t we trying to raise the level of public discourse on these issues?

    • Alex Bauman
      Alex Bauman July 18, 2014 at 11:04 pm #

      I cited one other source that found urban lanes could handle 1,600 cars per hour. But if you want to spend several hours researching and writing a post, Stacy, you’re welcome to do so. Unless you’re a… liar!

      • Bill Lindeke
        Bill Lindeke July 22, 2014 at 6:46 am #

        Yeah this post is entirely unresearched compared to most things on the internets.

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  1. Sunday Summary | streets.mn - July 20, 2014

    […] It’s Not a Bottleneck, It’s a Turkey Neck crunches the numbers to address whether there are too many lanes in the proposed redesign of the […]