Todd Litman

Accessibility vs. mobility

Founder, Victoria Transport Policy Institute, Feb 03, 10.

Tagged with transportation, urban planning, transit, transit oriented development, mobility, cars, vehicle miles traveled, accessibility

Let me wade into an ongoing debate among fellow Planetizen bloggers Samuel Staley and Michael Lewyn concerning the meanings of accessibility and mobility, and their implications for transportation and land use policy.

Accessibility is a general term referring to the ease of obtaining desired goods, services and activities. A number of factors affect accessibility including mobility (physical travel), land use patterns (the geographic distribution of services and activities), and mobility substitutes such as telecommunications and delivery services.

Transportation and land use planning decisions often involve tradeoffs between different forms of accessibility. For example, expanding roadways and parking facilities improves automobile access but tends to reduce pedestrian access, and therefore public transit access since most transit trips include walking links. A location convenient for automobile access, because it is located near a major highway intersection and has generous parking supply, is generally difficult to access without a car. Conversely, improving walking, cycling and public transit access often involves narrowing streets, reducing traffic volumes and reducing the supply of free parking, which reduces automobile access.

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Just as automobiles are machines that provide mobility, urban environments - villages, towns and cities - can be thought of as machines that provide accessibility by minimizing the distance among people and their desired goods, service and activities (shops, schools, jobs, neighbors, etc.). People who live or work in accessible, multi-modal communities, with a suitable mixture of public services within convenient walking distance tend to drive 20-40% less, and use alternative modes much more, than residents of conventional, automobile-oriented communities.

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In a recent blog, Samuel Staley argues that, with just a few exceptions such as Manhattan, NY, most North American communities lack the density required for multi-modal accessibility. According to his analysis the majority of North American communities are automobile-dependent - so “transportation” means automobile travel and “transportation improvement” means expanding roads and parking facilities, and maintaining low fuel and parking prices. I think his analysis overlooks some critical issues.

First, regional-scale density analysis fails to account for many factors that affect accessibility. For example, according to census data, Los Angeles is the densest urban area in the U.S., but many other communities are more multi-modal because of other attributes such as having good land use mix, concentrated commercial centers, connectivity, good walkability, pedestrian-oriented buildings, less parking supply and more parking pricing. Focusing on density confuses the issue by implying that multi-modal accessibility requires Manhattan-style land use patterns. On the contrary, many rural villages and small towns are relatively multi-modal because they have sidewalks on all streets, a nice downtown with a suitable mix of shops and public services, neighborhood parks, and regular bus service to nearby centers.

Second, conventional travel surveys tend to undercount and therefore undervalue walking and cycling because they often overlook short trips, non-work travel, off-peak travel, travel by children, recreational travel and the walking links of trips that involve motorized modes. ...