Summer greetings from Western Canada.
I am looking for guidance on how urban road connectivity affects per capita
vehicle travel, to incorporate into a new chapter of our Online TDM
Encyclopedia (http://www.vtpi.org/tdm/tdm116.htm).
The only quantitative information I've found so far is in the USEPA's
"Smart Growth Index (SGI) Model"
www.epa.gov/smartgrowth/topics/sgipilot.htm). The "Smart Growth Index
Indicator Dictionary," which describes the model details, on page 59,
defines the 'Design Index' as 0.0195 * street network density + 1.18 *
sidewalk completeness + 3.63 * route directness.
I'm pretty sure that this cannot be correct: it implies that sidewalk
completeness is two orders of magnitude more important than street network
density, which together have a pretty small elasticity. I would expect that
street connectivity will have a larger effect on vehicle mileage than
sidewalk connectivity, since more complete streets reduces vehicle trip
distances, while sidewalk connectivity will only reduce vehicle trips when
motorists shift to walking, and the implied impact is so small, it is
essentially insignificant and unmeasurable.
Please let me know if you know of any other methods of quantifying this
impact, or if you can explain how I might have misunderstood the Smart
Growth Index Model. Also, please let me know if you have other comments
about the new chapter.
Thanks for any help you can offer.
Sincerely,
Todd Litman, Director
Victoria Transport Policy Institute
"Efficiency - Equity - Clarity"
1250 Rudlin Street
Victoria, BC, V8V 3R7, Canada
Phone & Fax: 250-360-1560
Email: [log in to unmask]
Website: http://www.vtpi.org
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