This page is intended to provide a primer and reference to key documents relating to transit oriented development and transportation.
CO2 emissions are almost directly proportional to mpg (or mpgE). Some adjustment must be made to allow for the differences between diesel and gasoline engines.
Cars & Light Trucks
Cars and light trucks have made significant increases in fuel efficiency, overtaking transit which has remained near static. Assuming average occupancy of 1.67 passengers per car, cars and light trucks achieve 43.9 passenger miles per gallon. By comparison transit achieves only 36.2 passenger miles per gallon.
The higher the passenger miles per gallon, the lower the emissions (higher is better).
Comparison of Passenger Miles Per Gallon, 2010 Figures
The following chart shows passenger miles per gallon of different transit modes for the US in 2010 based on the same source data. It is important to consider the following when viewing this comparison:
- Fuel efficiency of cars and light trucks rapidly improved since these 2010 figures (Source EPA), but transit emissions have remained near static
- Whitehouse legislation mandates that new cars must achieve 54.5mpg by 2025 (multiply by 1.67 average occupancy and this translates to 91 passenger mpg). Clearly it will take some years before this becomes the average. One might expect this to be the average in the early 2030s (which is most likely a realistic midpoint for planning new rail projects).
- Adding additional transit to routes that do not have high passenger loads will further reduce transit passenger mpg (e.g. arterial services have a much higher pmpg than lifeline services)
- Efforts to switch people from using transit to cars will either:
- Have a minor beneficial effect for a small number of years; but the abatement cost will likely be prohibitive (projects should cost under $100/ton CO2 abated to be cost effective – see page 8 of this McKinsey report)
- Cause the opposite of the intended and actually serve to increase greenhouse gas emissions
Source Data: American Public Transportation Association’s 2012 Public Transportation Fact Book, Appendix A.
EPA Says mpg of Cars Sold in 2012 Hit Record
AutoBlog, Dec 15, 2013
Cars in the US Are More Efficient than Ever, Here’s How it Happened
Washington Post, Dec 13, 2013
Who Buys the Most Hybrid Cars? Northern Californians Survey Says
Forbes, Jan 3, 2013
2012 Traffic Counts on California State Highways
This document identifies the number of cars per hour (peak) at different points (typically freeway exits) along California’s freeways.
Golden Gate Transit Ridership
Golden Gate Transit official reports, Aug 2, 2013
Ferry ridership is up (but note that capacity is reaching limits and no additional crossings can be added). Bus ridership is down.