Monday, June 18, 2007

Separating trip generation and congestion effects

The latest Planning Department thinking on the zoning amendment to create a Planned Business District includes trip-generation maximums, which I discussed at great length below.

One thing I did not discuss below was the difference between exceeding trip-generation maximums and creating unforeseen congestion problems. It's an important distinction.

It would be possible for a development to exceed its trip-generation maximums and not cause any noticeable new pockets of congestion. Should the maximums be enforced in that case? Absolutely. We want to strictly manage volumes because traffic is pollution, even when it isn't causing acute crises, and because traffic volumes don't need to cause acute crises to be a problem. Traffic causes death by a hundred cuts. We need to reduce traffic volume (or at least manage it) for the sake of volume itself.

If a site exceeds its trip-generation maximums, a developer should not be able to get off the hook by acknowledging excess volumes but saying that, in effect, the volumes aren't creating any particular problems.

It would also be possible to create a new traffic problem without exceeding trip-generation maximums. A development like Chestnut Hill Square is going to generate significant new traffic, even in compliance with maximums. The best efforts of all the traffic professionals and community activists isn't going to anticipate and prevent or minimize all the secondary effects of the traffic.

Should the developer be responsible for remediating such problems after the fact? Not if they are under the trip-generation maximums. Maybe, you have the developer contribute to a fund for unanticipated problems, but there's no reasonable way to require the developer to fund remedies for all the unanticipated consequences of traffic.

Trip-generation maximums are fair and relatively easy to enforce. The City and the developer agree on numbers and a way to measure them. If the numbers are too high, the developer can take all steps necessary to reduce the numbers on-site.

Congestion consequences are not-so-fair and messy. You can never be sure that a congestion problem is attributable to a particular site or even mostly attributable. It isn't fair for a developer to be on the hook for an uncertain amount to fix a problem that wasn't anticipated. A solution to a particular traffic problem may be well outside the control of a developer. For instance, a solution -- like a new signal -- might require regulatory approval.

The version of trip-generation enforcement in the Planning Department's most recent memorandum reflects this confusion. It lists changes to nearby infrastructure as a measure that a developer might take to remediate excess volumes. While you might be able to change the infrastructure to reduce volumes, the recommendation suggests that the developer has to address effects of volume, not volume.

Better to hold the developer to the maximums, regardless of what effects traffic has, and limit the developer to on-site changes to get back under the maximums. That is not to say that the City should not require mitigation efforts in anticipation of traffic problems.

Traffic as pollution
Trip generation maximums

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