Promised traffic improvements

Mass. Ave FDR

Four Mass. Ave. traffic intersections flunk out on a scale where A–D are good and E–F are not.

That assessment, in the project’s functional design report, evaluates level of service based primarily on seconds of delay per vehicle.

The Town’s consultants take this further by also grading the intersections in the future, assuming a steady growth in traffic volume, for (1) no design change (“no build”) versus (2) reconstruction as proposed by the Town.

No-Build (NB) vs. Plan Over Time (am/pm peak)

Bates Orvis Lake Rt. 16
NB Plan NB Plan NB Plan NB Plan
Today F/F F/F F/F E/E
2018 F/F C/B F/F F/F F/F D/C E/E E/D
2028 F/F C/B F/F F/F F/F E/D F/E E/E

For instance: Lake street would go from straight Fs today to D/C (am/pm peak) in 2018; that degrades to E/D by 2028.

Of these four problem intersections, Orvis Rd. is not improved.

The grade for Bates is bumped up by the new traffic signal the plan would put there.

Lake St.’s improvements flow from the new lane configuration, which uses the width of one of today’s two westbound lanes to make dedicated left-turn lanes both ways on Mass. Ave.

Meanwhile, the slight improvements at Route 16 will only come to pass if the DCR and the City of Cambridge, who have jurisdiction over that intersection, adopt signaling changes recommended by the consultants. (The intersection is beyond Arlington’s authority.)

No one should oversell these improvements, but it makes sense that the changes will ease traffic flow a little bit. This analysis gives us a handle on that.

See for yourself. The current level-of-service grades for these and other intersections are explained in the Functional Design Report at page 21; future grades under the no-build scenarios are at pages 23–24; future grades under the proposed design are at pages 40, 41, 43–46, 48.


2 comments so far

  1. Donna Janis on

    The definition of D level of service is “approaching unstable flow”, so calling level D as ‘good’ is a stretch, Adam. Leaving out Route 16 which is not part of the Corridor Plan nor in Arlington, the chart shows that after spending $5.5 million we get zero improvement on Orvis and only marginal improvement on Lake which then degrades to level E (Unstable Flow) just five years after project work commences. So, the sole intersection ‘win’ is Bates Road which currently only has a queue of any note during morning rush hour and where the majority of residents are solidly against installation of a traffic light–and even Bates only improves to a level C in the morning post construction. After this huge expenditure and loss of traffic lanes to our main roadway, shouldn’t we expect a good and worthwhile Plan to deliver substantial improvement (to Level A and B service) to problem intersections? Your chart shows a sow’s ear, not a silk purse.

    • Adam Auster on

      I would never say that these modest, but real, improvements are either a silk purse or a sow’s ear. They are simply what they are. (For some real skepticism from me, look no further than this post.)

      The “D” grade is of concern because it might become an “E.” That’s real, but at “D” level it is providing good service. You are mistaken to suggest that only “A” and “B” are acceptable; indeed expending resources to change levels of service above “C” would be wasteful overkill in most cases.

      That’s why I took pains to stress that A-D are all acceptable, unlike a school report card.

      (Not sure what you meant about Lake St. being an “E” in 2018, might you have misread the chart?)

      I suspect we both know very well where the bottlenecks are on the corridor. They are not particularly tractable.

      The redesign would provide many tangible benefits and while it is unfortunate that the traffic-flow improvements are modest, they are about as good as we might reasonably expect (and are better than doing nothing, which in any case is not an option any more).

      To raise the levels of service at these intersection to A or B would probably require highway-grade engineering, such as flyovers and underpasses, inappropriate for a residential neighborhood. They would also be fantastically expensive, and their construction would be unacceptably disruptive.

      It sounds as though you think there is a way to improve the levels of service at these intersections within the context of a basic rebuild of the street, and without making the streets more dangerous. I should like to know what I am missing, and how this could be done.

      My sympathy about Bates Road; although the engineering evidence for this signal is strong it looks as though the crash history there is not much worse than that of several signalized intersections, so I think a case could have been made.

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