Let me try to answer my own question: How many people need to be on the bus for it to be beneficial?
A quick inquiry into the mighty Google brings us to the mighty Wikipedia, which tells us, and I quote:
- The fleet of 244 1982 New Flyer 40 foot trolley buses in local service with BC Transit in Vancouver, BC, Canada in 1994/95 consumed 35454170 kWh for 12966285 vehicle-km, or 9.84 MJ/vehicle-km. Exact ridership on trolleybuses is not known, but with all 34 seats filled this would equate to 0.32 MJ/passenger-km. It is quite common to see standees on Vancouver trolleybuses. Note that this is a local transit service with many stops per km; part of the reason for the efficiency is the use of regenerative braking.
- A diesel bus commuter service in Santa Barbara, CA, USA found average diesel bus efficiency of 6.0 mpg (using MCI 102DL3 buses). With all 55 seats filled this equates to 330 passenger-mpg, with 70% filled the efficiency would be 231 passenger-mpg, or 0.34 MJ/passenger-km.
Compared to the fuel efficiency of the average automobile today, at 36 miles per gallon, per passenger… what?
Oh man, I need to do math now, don’t I? Here goes (pardon the approximations; I don’t have a calculator):
Math: fuel economy
1 Gallon of gasoline = 132MJ, so the 9.84MJ/vehicle-km fuel consumption of a Vancouver bus translates to roughly 0.07 Gallons /km, or 0.1 Gallon/mile, or the energy equivalent of 10 miles/gallon gasoline. Note that electricity is more efficient than gasoline or diesel engines. The diesel bus gets a humble 6 miles/gallon, which is equivalent to 5.5 miles/gallon gasoline, becaues 1 gallon diesel = 1.1 gallon gasoline.
Since the average automobile has fuel efficiency of 34 miles/gallon, an automobile outperforms a trolley bus by 3.4 times, and a diesel bus by 6 times, with respect to amount of energy consumed.
This means: at least 4 to 6 people need to be on the bus for it to be more energetically favorable than having these 4 to 6 people drive their average automobile, from point A to point B.
If everyone drives hybrid cars, which has a fuel efficiency of 48 mpg in the city, about 8 people would need to be on the diesel bus to make it energetically favorable.
Math: Gas emission
How about gas emission? I know for sure that those diesel busses smell a lot worse than my Honda.
Another quick look on Wikipedia suggests that we can’t trust our nose: “While diesel’s 15% higher density results in 15% higher greenhouse gas emissions per litre compared to gasoline, the 20-40% better fuel economy achieved by modern diesel-engined automobiles offsets the higher-per-liter emissions of greenhouse gases, resulting in significantly lower carbon dioxide emissions per kilometre.“
In plain English, although burning a liter of diesel produces 15% more green house gas, that liter of diesel can drive your car 20-40% further. So you only need to burn roughly 0.7 liters of diesel when you need to burn 1 liter of gasoline, so you would produce 20% less green house gas if you use diesel instead of gasoline.
So, in plainer English, about 5 people would need to be on the bus to make produce less green house gas than driving automobiles, since a typical automobile outperforms a diesel bus by 6 times in fuel economy, it outperforms the same bus by 5 times in green house gas emission.
In Vancouver, you rarely see a bus that carries less than 20 people. And during rush hours, oh man, I sometimes wonder when the busses will bust their tires. In smaller cities, a bus also carries more than half a dozen people throughout the majority of its route.
Also, busses save a ton of space for the city’s streets, keep a ton of poor students mobilized (perhaps in a crammed, immobilized way), and make the city look good in general.
Besides, those busses will keep running even if you don’t take it. So instead of letting the # of passengers drop below the critical value of feel-goodness (ie. 6), let’s all put our cars away and hop onboard.
So I got no replies to what I thought was an interesting question about busses, over the course of 24 hours. I guess this goes on to show why having a high traffic to a blog is desirable for a blogger; the bigger the audience, the more likely someone would be interested in a post and responding to it. Perhaps I need to do more research on blog traffic and audience engagement?