Display cost for car+driver on a ferry, for example vs. transit fare

[Marcy]

This is crosspost from Google TransitPartners New Features &
Suggestions http://groups.google.com/group/google-transit-help-ideas/browse_thread/thread/cac9bd8a553f6f18#

Here is a sample of walking on the ferry vs. driving: http://tinyurl.com/27pgxyv

and it displays it is cheaper to drive $13.70 (based on distance/
mileage) than walk-on and pay $15.50; however, there is a known cost
for putting a standard motor vehicle on the boat and that cost is
minimum: $55 (shown here, http://cohoferry.com/main/?Fares)

Could we supply this actual cost to drive (car+driver) as a GTFS
extension as feed managers? What are the barriers to capturing and
displaying this "pretty simple fixed distance-based calculation"?

Perhaps where fares are excluded or omitted a cost to drive should
still appear?
(+new feature request)

while this calculation is not equivalent to the suggestion of CO2/
Carbon emissions that Joe Hughes posted in 2008
http://groups.google.com/group/gtfs-changes/browse_thread/thread/1416890017239faf/446e52a17dc330a1?lnk=gst&q=carbon#446e52a17dc330a1,
I find it goes quite a ways to helping riders make an informed
decision on the cost of driving.

Your efforts to build upon this feature request are appreciated!
Marcy