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Thread: Trip generation question

  1. #1

    Trip generation question

    I been reading on these forums that it usually depends on the type of bussiness and the square footage which determins how many parking spaces are required along with the amount of trips that will be generated.

    But what about the population density of an area? Is it taken into consideration at all? To me this would be a huge factor, maybe even more important then the square footage.

  2. #2
    maudit anglais
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    Re: Trip generation question

    Originally posted by OfficialPlanner
    I been reading on these forums that it usually depends on the type of bussiness and the square footage which determins how many parking spaces are required along with the amount of trips that will be generated.

    But what about the population density of an area? Is it taken into consideration at all? To me this would be a huge factor, maybe even more important then the square footage.
    Excellent question. I'll address the trip-generation portion first.

    The Institute of Transportation Engineers (ITE) Trip Generation "bible" has become the standard reference material when undertaking a traffic impact study. It is backed up by decades worth of field studies looking at actual trip generation rates for almost any land use you can think of.

    That being said, we don't use it - except for comparative purposes, or for select (typically auto-oriented) land uses.

    The field survey data which comprises the Manual is taken almost exclusively from developments in suburban areas (where most new development occurs). Suburban areas developed since the end of WWII are typically auto-oriented, with the result that ITE trip rates do not represent an accurate trip-generation projection for areas with better pedestrian/cyclist/transit access.

    We have developed our own set of field survey data, and typically require traffic consultants to provide proxy trip-generation data in support of their trip rates (e.g. survey a similar development in a similar location). Some consultants adapt ITE trip rates by using census or Transportation Tomorrow Survey (TTS - major transportation survey undertaken across the Greater Toronto Area every five years) data to reflect local conditions in regard to modal split, auto occupancy and other trip-making inputs - although this can be tricky.

    The population density of an area in and of itself may not give an accurate idea of how many trips a development will generate - but it is likely that it will have an impact on how many auto trips that development will generate. Some land uses (gas stations, drive-thru restaurants, car washes) will tend to generate similar trip numbers no matter where they are located.

    As for parking generation, the ITE has a manual for that too, and we don't use it either. I don't think I've really ever looked at it. We go by our own parking rates, which are quite low. And this can be attributely to the higher population densities and thus greater use of transit, cycling, and walking that we have. In smaller towns, which may not have the resources to develop their own parking (and trip gen for that matter) rates based on their unique circumstances, use of a standard reference such as the ITE manual is the best recourse.

    One caveat - parking by-laws almost always supply a minimum parking rate. There is nothing to stop a developer coming in with a higher rate if that is what they feel they need. Luxury condos supplied over 2 parking spaces per unit in a downtown setting are my pet peeve right now!

  3. #3
    Interesting, thanks. It's surprising that ITE has been given this much authority in traffic planning, especially when their publications become dispensable in most urban areas. For the suburbs it sounds like good reference material but hardly a bible.

    One caveat - parking by-laws almost always supply a minimum parking rate. There is nothing to stop a developer coming in with a higher rate if that is what they feel they need. Luxury condos supplied over 2 parking spaces per unit in a downtown setting are my pet peeve right now!
    With the volume and capacity issues that exist downtown it's only a matter of time before Council lays down some strict limits on parking. Once travel times start to exceed 1 hour from your typical suburban councillors house to City Hall, I can guarantee you a change in the parking by-laws will follow .

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