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What we can say is that GLX will power low-emissions growth in Som/Med, and easy access to high-wage employment centers.
We cannot say that it will solve any existing road or pollution problems, except that some will be given a fast, clean alternative to those road problems (which will remain).
Matthew's point about induced demand trumps this. If it becomes known that traffic volumes are down and average speeds are up, commuters form Woburn, Stoneham, and Melrose will quickly discover (via Waze/GMaps/AMaps/GPS) that they can drive more often and be happier if they take a shortcut on 16, 60, or 99 etc. [We saw the EXACT same thing when the Big Dig opened...once AssemblySq-SouthBay was decongested, it was suddenly worth congesting I-93 between Assembly and Roosevelt Circle (Fellsway West /Medford) to "wait in line" for your chance to use the "less congested" Central Artery. In effect, it moved the jam northward]
Induced demand will be a mix of people discovering new, faster/less stressful routes and people, say, joining a gym or dance class choosing a private school or new job (or Wegmans!) slightly further from their house.
The GLX's road benefits, instead of accruing to local Medford/Somerville drivers, will mostly accrue to Winchester-Woburn-Stoneham-Malden-Melrose drivers who are given a new "back way" to get places by cutting through Som/Med/Camb roads that commuters are no longer using.
Given this, it is folly to say that the GLX is good for reducing VMT or meaningfully reducing pollution (and the CLF knows this and so do the Courts)
In fact, [the car fleet] now pollutes something like 1/5 to 1/10th what they did when the Big Dig settlement was signed, so even doubling traffic still halves or fifths the pollution, thanks to the retirement of wave after wave of dirty cars (pre-1980 (guzzlers), pre-1989 (dirty sippers), which would have been most cars back then, and then 1989-1994, then 1994-1999, and now even the 1999-2003 are starting to be retired)
If the goal of the GLX was x% reduction in pollution, the reality is that it has already been achieved--and more--thanks to engine technology (and you could probably double VMT through the GLX area and still be below the original emissions goals)
You can basically draw a chart like this for any known pollutant/irritant (VOCs are "gas fumes" that cause smog, but you can do it with NOx, CO2, or particulates and it looks about the same) Source:US EPA
We cannot say that it will solve any existing road or pollution problems, except that some will be given a fast, clean alternative to those road problems (which will remain).
The GLX transit studies do project reduction in vehicle miles traveled. The ridership projections are not all transit users today. Whether you believe them or not, the projected reduction is more than 25,000 vehicle miles PER DAY. Will that free flow traffic, I do not know, but it is a lot of travel on the major arteries through Medford and Somerville not just I-93, but also 16, 28, 38, probably even 99 in Charlestown... And backup on the surface roads contribute to I-93 backups (they are the bail-out routes).
http://greenlineextension.eot.state.ma.us/about.html
Matthew's point about induced demand trumps this. If it becomes known that traffic volumes are down and average speeds are up, commuters form Woburn, Stoneham, and Melrose will quickly discover (via Waze/GMaps/AMaps/GPS) that they can drive more often and be happier if they take a shortcut on 16, 60, or 99 etc. [We saw the EXACT same thing when the Big Dig opened...once AssemblySq-SouthBay was decongested, it was suddenly worth congesting I-93 between Assembly and Roosevelt Circle (Fellsway West /Medford) to "wait in line" for your chance to use the "less congested" Central Artery. In effect, it moved the jam northward]
Induced demand will be a mix of people discovering new, faster/less stressful routes and people, say, joining a gym or dance class choosing a private school or new job (or Wegmans!) slightly further from their house.
The GLX's road benefits, instead of accruing to local Medford/Somerville drivers, will mostly accrue to Winchester-Woburn-Stoneham-Malden-Melrose drivers who are given a new "back way" to get places by cutting through Som/Med/Camb roads that commuters are no longer using.
Given this, it is folly to say that the GLX is good for reducing VMT or meaningfully reducing pollution (and the CLF knows this and so do the Courts)
In fact, [the car fleet] now pollutes something like 1/5 to 1/10th what they did when the Big Dig settlement was signed, so even doubling traffic still halves or fifths the pollution, thanks to the retirement of wave after wave of dirty cars (pre-1980 (guzzlers), pre-1989 (dirty sippers), which would have been most cars back then, and then 1989-1994, then 1994-1999, and now even the 1999-2003 are starting to be retired)
If the goal of the GLX was x% reduction in pollution, the reality is that it has already been achieved--and more--thanks to engine technology (and you could probably double VMT through the GLX area and still be below the original emissions goals)
You can basically draw a chart like this for any known pollutant/irritant (VOCs are "gas fumes" that cause smog, but you can do it with NOx, CO2, or particulates and it looks about the same) Source:US EPA
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