Accessibility David Levinson

Why Cities Form? Why does the Twin Cities exist? Why are the Twin Cities larger than Duluth or Fargo? Why is Chicago more important than St. Louis? What is inevitable, what is chance?

Accessibility A measure that relates the transportation network to the pattern of activities that comprise land use. It measures the ease of reaching valued destinations. Accessibility “is perhaps the most important concept in defining and explaining regional form and function.” (Wachs and Kumagai 1973)

LeCorbusier LeCorbusier, the controversial twentieth century Swiss architect and planner once said “A house is a machine for living in” Villa Savoye, 1928

Machine for Access Transportation is “The Machine for Mobility” Our legs, our wheels, our tracks, our roads, our wings help us move. We know that since the buildout of the Interstate, mobility has been decreasing (due to congestion) But we cannot assess the system as a whole unless we know what we are moving to. The City is “The Machine for Access” The formation of the city allows us to reach more things in less time. Transportation is necessary, but so are the activities,(located at places) to be reached. Change in land use may mean that despite increasing congestion, we still have rising accessibility

Mobility vs. Accessibility Manitoba High Speeds Few Destinations High Mobility Manhattan Low Speeds Many Destinations High Accessibility

Measuring Point Accessibility Where: A i = accessibility at point i P j = some measure of activity at point j (for example jobs) C ij = the cost to travel between i and j (for example travel time by auto).

f (C ij ) For auto: For transit: Where: C ija = peak hour auto travel time between zones i and j; and C ijt = peak hour transit travel time between zones i and j.

Isochron: How Far Can You Go in a Given Time Multiply by number of things in each ring See how it changes over time. Works for individual points. Need to see region as a whole.

Metropolitan Accessibility where: A = Accessibility W i = Workers at origin i Ej = Employment at destination j f(Cij) = function of the travel cost (time and money) between i and j.

Relative vs. Absolute Change Or do people value the relative change (I will pay twice as much for a network that is covers twice the percentage of the market)? Do people value the absolute increase (each person I am connected to adds the same value)?

Absolute vs. Relative Accessibility A transportation improvement reduces the travel time between two places. What happens? The absolute accessibility of the entire region increases. The pie increases The relative accessibility of the two places increases at a greater rate than the rest of the region. The slice of the pie going to those two places increases even more. Why does this matter?

Accessibility and Land Use

Coruscant

Constraints If the model is correct, why don’t we live on Coruscant? –Time - we just don’t live there yet –We do, visit New York, Tokyo, Hong Kong –Congestion and related costs to density limit the accessibility machine –Population, food, energy are constraints Or maybe it is just this guy

Access By Mode & Distance (DC 1988)

Journey to Work Time and Home Value by Ring (DC 1988, 1991)

Project: Phase 1 Review Literature on Performance Measures, System Data Characteristics, and Accessibility. Define Performance Measures for Accessibility. Illustrate Performance Measures using hypothetical or limited available data for “proof of concept”.

Ultimate Aim: Multi-Modal & Multi-Purpose Accessibility Over Time JobsLaborShopsPlayOther Auto Transit Walk Bike

Requirements Point to Point travel times for all points –On limited access freeways (and ramp meters), –linking roads (signalized arterials) and –local roads, –by transit, walking, biking Land uses / Activities for all points in region

Questions