proposal: specifying CO2 emissions for transit routes

[Joe Hughes]

Summary:
Add a way for feed publishers to indicate the carbon dioxide emissions
of public transit routes.

Motivation:
Several agencies have expressed an interest providing CO2 emissions
information to riders, so that riders can compare the impact of taking
public transit to driving. Carbon dioxide impact calculations are
still a tricky business, but it might be helpful to provide a rough
estimate as a first pass, especially if agencies can provide values
based on their local conditions.

Proposal:
The following field would be added to routes.txt:
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co2_per_km (optional):
The co2_per_km field allows the agency to specify how many grams of
carbon dioxide are emitted for each kilometer that a passenger travels
on this route. The value should be an integer, and should reflect an
individual passenger's "share" of the emissions, rather than the total
emissions of the vehicle. If no emissions information is available,
the field should be omitted or left blank (as a value of "0" indicates
a route with no carbon emissions).
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Discussion:
This is a value that's controversial and tricky to calculate.
Ideally, a passenger's "share" of the emissions would reflect how many
passengers are on the vehicle at that point, but realistically, most
applications aren't going to have such detailed information.
Providing a per-route average allows the agency to incorporate the
factors that they think are important based on their knowledge of
their operations.

Your thoughts?

Joe Hughes
Google