2. Time and Space David Levinson

3. Accessibility David Levinson

4. Why Do 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?

5. 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)

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

7. 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

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

9. The Power of Networks Top picture: two “markets”: A-B and B- A. Middle Picture: six markets: B-C, C-B, C- A, A-C Bottom Picture: twelve markets: D-C, C-D, D- B, B-D, D-A, A-D

10. Mathematical Expression S = N ( N-1) S = “Size” of the Network N = Number of Nodes (places) To illustrate With 2 nodes: S = 2*1 = 2 With 3 nodes: S = 3*2 = 6 With 4 nodes: S = 4*3 =12. And so on.

11. 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.

12. 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.

13. Measuring 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). A = Overall Accessibility W i = Workers at origin i

14. Network Size vs. Accessibility Network Size: All nodes valued equally Independent of type of node Independent of spatial separation of nodes Accessibilty: Places are not equal Places (i, j) are weighted according to size Considers spatial separation of places.

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

16. 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?

17. Feedback: Positive and Negative Positive Feedback Systems More begets more Less begets less. Examples? Negative Feedback Systems More begets less Less begets more. Examples?

18. Accessibility and Land Use

19. Coruscant

20. 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

21. Access By Mode & Distance (DC 1988)

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

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

24. 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

25. Questions Is congestion rising? Are commutes getting longer? Are people spending more time commuting? Are people spending more time traveling? How do the declining trip times and increasing speeds reconcile with the general perception of worsening congestion? What do travel and activity depend on? Is spatial determinism correct? Does income matter? Does location matter? Does demographics matter?

26. Is Sprawl the Problem or the Solution If Sprawl is the Solution … what is the problem? [ …. ]

27. Rational Locator Hypothesis “Rational Locators,” including both individual households and firms, respond to changes in transportation supply by siting themselves to reduce commuting times … The key policy implication we see is that over the long term, individual Locators act rationally to balance total costs as measured in dollars and minutes, and total benefits, as measured in proximity, space, and other preferences. These individual calculations result in the polycentric, and dispersing, urban form that exists today throughout the United States. (Levinson and Kumar 1994).

28. Restating The Rational Locator Hypothesis thus posits that individuals can, if they choose, maintain approximately steady journey-to-work travel times in the face of rising congestion and increasing distance between home and work by adjusting their home and workplace. Dispersion and decentralization are conscious choices that enable rational locators to achieve their goals. Consistent with, but not implying travel time budget hypothesis.

29. Evidence Large number of studies have shown consistency in gross travel budgets. However, average travel times in many metropolitan areas seem to be rising (Census data)

30. Jobs and Housing Accessibility and Commuting Duration In the gravity model implicitly being tested here, average commute to work time is determined by three factors: 1) a propensity (choices) function which relates willingness to travel with travel cost or time, (individual demand) 2) the opportunities (chances) available at any given distance or time from the origin, (market “supply”) and 3) the number of competing workers. (market demand) Propensity = f ( t ij, Income, Mode, Gender... ) It is hypothesized that this underlying preference is relatively undifferentiated based solely on location.

31. Illustration of Gravity Model

34. Implications of Gravity Model As city size increases, mean commuting time increases (we have a left-truncated distribution, so as the right branch extends outward, the average must increase). Travel time, is largely independent of density – except to the extent that density changes network speed. If preferences shift, mean travel time will change inward or outward. If congestion rises, more opportunities will be farther away in terms of time, and fewer nearby – implying that average commuting time rises.

35. Actual Data Travel to Work Times for Albany and Anchorage (vertical line is the mean)

36. Inter-Metropolitan Data Summary

37. Regression Results for Mean Commuting Time

39. Rational Allocator Hypothesis Changes in Time Allocation due to rising female labor force participation can be understood in context of Bounded Rationality “Allocators” - shape temporal activity patterns within household, spending time and money to produce household goods, maximizing utility. Technology, rising per capita income, and labor force participation create substitution of in-house activities by out-of-home activities. E.g. eating out, day care.

40. Activity Duration Calculation

41. Activity durations per day, in minutes, for 1968, 1988 and 1994, Washington D.C. adults 18-65

42. Activity duration per day, in minutes, for 1990 and 2000, Twin Cities, adults 18- 65

45. Resolving the Paradox Suburban Arterial Urban Radial 1968 Speed55 MPH25 MPH 1988 Speed40 MPH20 MPH 1968 Traffic10%90% 1988 Traffic50%

46. Weighted Averages While Speed drops on both facilities, Average Speed rises from 28 MPH to 30 MPH. More generally, speed can drop on every facility from the day it opens as traffic increases, but if people increasingly use higher speed facilities, that use will outweight the speed drop. This may be of little comfort to the commuter whose work trip becomes worse every year until he relocates.

47. Myths? 1.The long commute is commonplace 2.Jobs Housing Balance doesn’t matter 3.‘Sprawl’ makes congestion worse 4.Travel times are rising 5.Transit investment will lower travel times 6.Most travel is work trips

48. For More Knowledge PA8202 - Networks and Places PA5202 - American Cities 2

49. Questions