Cut-through traffic

Many are worried about the redesign’s potential to increase the number of cars leaving Mass. Ave for side streets.

The fear is that either the lane configuration or (especially) the placement of traffic lights will cause delays, causing drivers to seek alternate routes.

Are these fears realistic? It’s a hard issue to discuss because it’s so murky. As Laura Wiener, the senior town planner assigned to the project said (at the June 16 meeting of the Mass. Ave. Review Committee), the question entails personal choices that may not be rational or predictable, and therefore can’t be modeled or projected. (Not a direct quote by any means.)

Actually, based on some of the things I learned at the two committee meetings, I think she is wrong. It is possible to model all kinds of behaviors, rational or not. Here are two examples of how you could think about this problem in terms of Mass. Ave.

First, you could assume that people take take the quickest routes to where they are going — that they take alternate routes to save time.  There may be a few exceptions to this, but it’s a defensible assumption.

A model based on this assumption would use actual traffic data to determine whether the proposed changes would turn Mass. Ave. into something that is no longer the route of choice. Here are the major changes.

Mass. Ave. Eastbound would be two lanes of motor-vehicle traffic, very similar to the way it is today. No change.

Mass. Ave. Westbound would be one and a half lanes — a through-traffic lane and turning lanes — along many stretches. This is a change, but since the capacity of this design exceeds not only today’s traffic peak but the peak traffic projected for 2018, there is no increase in trip time. (Traffic might even flow better, thanks to the turning lanes.) Mass Ave. Westbound, in other words, would still be as fast as under the current (old) design.

There would be one new traffic signal on Mass. Ave. under the proposed plan, at Bates Road. This signal will be synchronized in some way with the (existing) light at Linwood St., but still has the potential to add a light cycle to a trip down Mass. Ave., and that means a longer trip. Not every time, but sometimes.

With this change, do alternate routes make sense? The light cycle might be 40 seconds. I suggest that any alternate route would take longer than that. Look for yourself (map). Again, no effect on cut-through traffic.

The net result is, no additional cut-through traffic as a result of the proposed design.

The second way to model the issue is to assume that cut-through traffic will be proportional to traffic volume in general. This is questionable, but it gives us a way to think about the problem. The consultants who’ve developed this proposal for the town tested it against a scenario of 1% growth in traffic volume per year, about a 10% increase by 2018.

Historically, the growth rate has been slower, and the consultants don’t actually think traffic will grow at that rate. But they modeled it that way to be cautious, so let’s do the same thing.

Under these assumptions, cut-through traffic will grow by about 10% by 2018. If your street gets 30 cars cutting through at rush hour today, it will get 33 in ten years.

Here’s the kicker: How much of that 10% is due to the redesign? The answer is none of it.

The proposed design accommodates all of the traffic volume, even in 2018 with the 1%-growth assumption. Even though there is growth in traffic volume, none of it is due to the redesign. Since 0% of 10% is zero, the new design has no impact on cut-through traffic.

All this is a long-winded version of something that Jack Hurd said at one of the committee meetings (again, not at all a direct quote): Since the redesign will not increase trip time, we do not think there will be any effect on cut-through traffic.

I agree.

4 comments so far

  1. Chad on

    Adam nice post. I think the concern about cut through traffic is over blown at best and smokescreen for killing the project at worst. While I think it is difficult to model/predict cut through traffic, it isn’t difficult to obtain data on it. I think opponents to this plan should work with us and the town to do a traffic study post Mass Ave to determine which streets have high levels of cut through traffic (likely the same one’s that have it today) and mitigate that cut through using signs, speed tables, etc. This is definitely feasible. In my neighborhood of South of Mass Ave, East of Lake posting people a couple days at entry streets and exits streets and cross check cars that enter and exit would give you a good idea of where the traffic is coming from and how to mitigate it.

    The truth of the matter is opponents have latched on to the cut through traffic argument because it is the most nebulous one there is. They still don’t recognize the validity of the multiple traffic counts that have been done because they don’t validate their point of view.


  2. Adam Auster on

    Thanks, Chad.

    I do believe that anxiety about this issue is genuine and not limited to those who just seem to be looking for any reason at all to be against the project.

    I’ve had some very surprising discussions with both friends and strangers with these concerns, most having to do with traffic signals.

    Some of the scenarios that worry them struck me as fantastic at first. However, if there’s one thing I have learned about traffic it’s that the whole thing is studded with surprises and that gut reactions are a poor guide. That includes mine.

    Ultimately, I do think these fears are unfounded, for the reasons I describe. Cut-through traffic is a real issue, but is not exacerbated by the proposed redesign. But I reached that point of view by taking those concerns seriously, which I think they deserve.

  3. Mark K. on

    Yes, its all predictable.

    After changes, Mass Ave/Rt 3 may not congest under normal circumstances, but delivery trucks, Police stops, Police/Fire response, traffic accidents will all create ephemeral congestion events which will increase total cut-through’s.

    I agree total cut-through won’t increase under normal circumstances, HOWEVER, which streets are used Will change. If you add a signal to a street, adjacent streets will be used instead, like Whack-a-mole. My street, Palmer, has high cut through because drivers avoid two lights in a row on Franklin st. if they come from Warren St., and Rt. 60 Medford. Its the fastest path from West Medford to Porter Square during commuting hours, avoiding the left turn from Rt. 16 to Mass Ave, Cambridge.

  4. Mark K. on

    Bone-head DOT “safety” measures with unintended consequences:

    1. Energy Star traffic lights with LEDs. In Minneapolis they caused traffic accidents and killed people. Combined with shades to keep side traffic from anticipating light changes, snow and ice collects and blocks the light. LEDs are too cold to melt snow/ice so city workers have to go out and manually scrape them. Alternative is buying expensive plastic shields which will haze and need periodic replacement. Oops.

    2. Car air bags – they kill children and small adults. Fix is to allow a switch to turn them off and ban kids from front passenger seat. Now, can’t buy a smaller fuel efficient car if you have kids.

    3. Child safety seats + front airbags = more gas guzzling SUVs which are less back breaking and faster to get kids in and out of. Parents of more than 2 kids under 7 need 3-row SUVs – can’t fit 3 car seats on a back seat.

    4. More SUVs = poorer visibility of pedestrians and more death for them. SUVs = parents backing up over kids they can’t see. More SUVs mean worse outcome for small, fuel efficient cars in accidents (solution, 800lb more steel for crash protection and worse efficiency). Higher vehicles easier to get kids in/out, but roll over easier.

    5. Cash for clunkers – parents whose kids outgrew car seats benefited the most, trading SUVs and minivans for 4dr. sedans since seats no longer needed.

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