How Many People Need to Ride the Bus?
I am currently in Germany doing what is lovingly referred to as a life cycle assessment "boot camp." Today we are "freestyle" modeling different problems to find some preliminary results and present them this afternoon to our colleagues.
Our question: how many people need to take the bus for it to be equally or more efficient than driving alone in a car? So we did what we'd call a quick & dirty calculation using recognized life cycle database information available in GaBi LCA software. Although there are no available stats on diesel buses in the database we were using, we grabbed data for a 9.3 tonne diesel truck and scaled it to a bus to make it more or less the same. We also grabbed diesel passenger car data for 1.4 — 2 liter engine vehicles. We compared here only the use phase for these two vehicles due to time and data restraints (we basically had 3 hours to discuss, define, model and present our results).
We only looked at fuel use and direct vehicle emissions and we did not include the production of the bus or vehicle maintenance. The impacts we considered are dust particulate matter, global warming potential and acidification potential for one passenger over one kilometer.
Our results were actually pleasantly surprising given that a bus weighs on average about 11 times as much as a car (11 tonnes vs. 1 tonne). Check out the graph of results below. The numbers show the number of people needed on a bus to break even with the impacts of a single-passenger diesel car.
What it basically means is that to "break even" with the impacts of driving alone in your car, a bus need only carry between 3 and 8 people! That's really very few people. So don't let them tell you that public transportation isn't worth it. It is totally worth it! Really, how often do buses really drive around empty? Hopefully the answer is never, if we to continue to choose the bus over the car.
Reminder: this is a really simplified assessment and is only for the purposes of getting a rough answer.
More on Sustainable Transport:
We Can't Believe Everything We Read: Hybrids and Hummers:
How to Green Your Public Transportation
Have You Reduce Your Dependence on Cars?
"Change Your World" Encourages Alternatives to Car