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To : Liz Epstein, Cambridge Community Development Department
From : Stephen H. Kaiser, traffic analyst
SUBJECT: Traffic Signal Timing and the Potential for Traffic Mitigation at Alewife
Thank you for mailing me copies of the original Rizzo scope letter on the Alewife Center project and the traffic counts made by Rizzo Associates in 1995 and early 1996 at Alewife. Unfortunately, some of the traffic counts are illegible and this is true of both copies I received - - the problem likely is a poor quality original. Under the circumstances, whoever supplied these counts should provide you with legible replacement copies, at no cost to the city. There is no excuse for submitting illegible traffic data.
As I noted in my March 10 letter to Stuart Dash, the Rizzo counts for the City are more extensive than the counts made for Alewife Center. With a 48 hour count, the data shows some remarkable traffic flow results. Near Whittemore Avenue on the parkway, there is a noticeable drop in actual traffic flow during the 5-6 PM peak period. In October 1995, the peak hour flows actually dropped by almost half.
I have been trying to think of all the possible explanations for this strange
drop in traffic.
The signal timing at Route 2 and Alewife and at the MBTA station is also not very efficient. Sample counts I have made indicate that signal operation on a 60-second cycle could actually produce a 5% capacity benefit, compared to the current operation on a 120-second cycle. The long queues produced by a 2-minute cycle also extend back to the MBTA station signal and Rindge Avenue.
Overall, I find the long signal cycles producing longer queues, longer delays, and reduced capacity due to the influence of short lane effects. The only benefits of long signal cycles -- reduced start-up losses -- appear to be totally overwhelmed by the magnitude of the short- lane losses at Alewife.
Regardless of the status of a formal MEPA filing for Alewife Center, we can engage is a useful discussion of the traffic limitations and potentials at Alewife. Indeed, the committee report to the City Council in mid-May should probably focus on these matters, as long as the specific development proposal is still in flux. I would note that if we were to consider a site proposal with additional office development, we would need to look at morning peak hour operations as well for any mitigation potential.
The Cambridge traffic counts contain useful information which has not been fully appreciated by City officials. Instead of the obvious initial conclusions that one might draw -- the Alewife area is congested and cannot accept any significant increase in traffic -- it appears that there does exist significant traffic improvement potential without having to go to the extremes of Salvucci's Wall. We should seek to define how to go about achieving these improvements and estimating the magnitude of change likely in traffic capacity.
With regard to a philosophy of traffic capacity enhancements, I concur with the City policy of not seeking to provide increased through capacity for vehicles entering Cambridge. However, in the afternoon, with the vehicles already in the City, there is a convincing logic which says that Route 2 and the Parkway should operate as best as possible to dissipate these vehicles, with a minimum of congestion and pollution. At the same time, residential streets should not be targeted for "mitigation" in the form of increased capacity -- especially the intersection of Rindge Avenue and Sherman Street. Some of the capacity improvements at Mass. Avenue should come in the form of less traffic on Rindge Avenue and more capacity on Mass. Avenue. Currently, even at 6:30 PM, traffic is backed up and not clearing out on Mass. Avenue, waiting to make a left turn onto the Parkway.
As I noted in my earlier comments, the real "heart of Alewife" may be at Mass. Avenue -- not Route 2. The Route 2 intersection may back up into Rindge Avenue, but Mass. Avenue backs up into Route 2 and makes Rindge significantly worse. Currently, we do not have a traffic analysis model which reflects these practical limitations at Mass. Avenue, Route 2 or Rindge Avenue. We do not know how to deal with queues, short lanes, and merging lanes -- all of which are critical factors at Alewife. The Highway Capacity Manual is batting 0 for 3.
Please send me any further traffic counts you have made in the Alewife area, from Huron to Mass. Avenue. Insist that they be provided to you in legible form, in 15-minute increments.
Contact the Alewife Study Group, North Cambridge Massachusetts, by email at email@example.com