Are Passenger-Miles a Valid Measure of Anything?

Every so often, one sees an article arguing that one mode of transportation is cheaper, more efficient, or less dangerous than another because it uses less energy/kills more people/costs more per passenger-mile. (1) It seems to me, however, that per passenger-mile comparisions are flawed in one key respect: they assume that trips on any mode of transportation will involve the same mileage, so that if the average driver lives 20 miles from work, the average bus rider will also live 20 miles from work.

2 minute read

January 15, 2010, 9:30 AM PST

By Michael Lewyn @mlewyn


Every so often, one sees an article arguing that one mode of
transportation is cheaper, more efficient, or less dangerous than another
because it uses less energy/kills more people/costs more per passenger-mile. (1)

It seems to me, however, that per passenger-mile
comparisions are flawed in one key respect: they assume that trips on any mode
of transportation will involve the same mileage, so that if the average driver
lives 20 miles from work, the average bus rider will also live 20 miles from
work.

This assumption does not square with empirical reality. In the real world, people who live far from
work tend to drive more often than people will live closer to work; the combination of long distances and the existence of multiple stops makes public transit far less convenient for someone who lives 10 miles from work than for someone who lives 2 miles from work. This is true even where transit service extends far into suburbia. For example, in
Toronto, which has a long-distance commuter train system, 58 percent of commuters living less than 1 kilometer (0.6 miles) from
work use non-automotive transport, as opposed to 35 percent living 1-4
kilometers (0.6 miles to 2.5 miles) away, and only 22 percent living more than
15 kilometers (9 miles) away.

In cities
lacking long-distance commuter train systems, the differences between
short-distance and long-distance commuters are even greater. In Edmonton,
for example, 25 percent of people living 1-4 kilometers from work commute by foot, transit or bike,
as opposed to only 2 percent of people living 15 kilometers or more from work.(2)

So in the real world of city planning, our choices are not between a city of 20-mile bus commutes and a city of 20-mile car commute. Rather, our choice is: do we want to make cities more compact, thus increasing the number of short commutes (some of which will typically involve transit, for the reasons stated above) or do we want to create a relatively spread-out city with lots of long commutes (most of which will usually be by car)?

In the compact city, fewer passenger-miles will be traveled, which means that all the negative externalities of travel (e.g. pollution, collisions, public costs) will be lower. And because people will be somewhat more likely to use transit and carpool, both cars and transit vehicles will be more fuel-efficient, because cars and buses are more fuel-efficient when they have more passengers. By contrast, in the car-oriented, spread-out city, both car and transit commutes will typically be longer, and both cars and buses will have fewer passengers.

(1) For anti-transit
examples, see http://www.cato.org/pub_display.php?pub_id=9325
http://saveportland.com/Car_Vs_Tri-Met/energy-cost-death-02d.htm
; for a pro-transit example, see http://hugeasscity.com/2009/03/22/your-co2-emissions-per-mile-may-vary/


(2) http://www12.statcan.gc.ca/english/census06/analysis/pow/pdf/97-561-XIE2006001.pdf
at 34-35
.


Michael Lewyn

Michael Lewyn is an associate professor at Touro University, Jacob D. Fuchsberg Law Center, in Long Island. His scholarship can be found at http://works.bepress.com/lewyn.

stack of books

Planetizen’s Top Planning Books of 2023

The world is changing, and planning with it.

November 24, 2023 - Planetizen Team

Close-up of 'Red Line Subway Entry' sign with Braille below and train logo above text in Chicago, Illinois.

Chicago Red Line Extension Could Transform the South Side

The city’s transit agency is undertaking its biggest expansion ever to finally bring rail to the South Side.

November 24, 2023 - The Architect's Newspaper

Diagram of visibility at urban intersection.

How ‘Daylighting’ Intersections Can Save Lives

Eliminating visual obstructions can make intersections safer for all users.

November 27, 2023 - Strong Towns

People walking on paved path in green city park with trees and tall city skyscrapers in background.

Green Spaces Benefit Neighborhoods—When Residents can Reach Them

A study comparing green space and walkability scores found that, without effective access to local parks, residents of greener neighborhoods don’t reap the health benefits.

December 3 - American Heart Association News

Aerial view of Eugene, Oregon at dusk with mountains in background.

Eugene Ends Parking Minimums

In a move that complies with a state law aimed at reducing transportation emissions, Eugene amended its parking rules to eliminate minimum requirements and set maximum parking lot sizes.

December 3 - NBC 16

White, blue, and red Chicago transit bus at an urban bus station with shelter.

Chicago Announces ‘Better Streets for Buses’ Plan

The plan establishes a ‘toolkit’ of improvements to make the bus riding experience more reliable, comfortable, and accessible.

December 3 - City of Chicago

News from HUD User

HUD's Office of Policy Development and Research

New Updates on PD&R Edge

HUD's Office of Policy Development and Research

"Rethinking Commuter Rail" podcast & Intercity Bus E-News

Chaddick Institute at DePaul University

Write for Planetizen

Urban Design for Planners 1: Software Tools

This six-course series explores essential urban design concepts using open source software and equips planners with the tools they need to participate fully in the urban design process.

Planning for Universal Design

Learn the tools for implementing Universal Design in planning regulations.