I love the premise of the Green Cab taxi company that started operating in the City this year. Sexy! Green! Buzzwords!

Their cabs DO look good on the street. They stand out and offer clear differentiation from other cabs both during the day with their bright green paint jobs and at night with their bright green toplights.

But, is it really possible to have a “green” taxi?

No. Taxis are inherently a non-green form of transit, but they can (sometimes) offer a few green advantages over personal vehicles.

Let’s look at an example trip. Suzy wants to come downtown to do some shopping. She didn’t call a cab in advance but she knew it wouldn’t be tough to hail one on the street since its early in the day. It’s a 5 mile trip from her home to the shopping district. But, the cab drove more than 5 miles to get Suzy to her destination. The cabbie was driving around (“cruising”) for fares. On a good day I can pick up 30 people driving about 150 miles during a shift which works out to be 5 miles per person. But, each person didn’t necessarily go 5 miles, they could have gone just a few. A good deal of those 150 mies is cruising mileage.

So Suzy’s trip actually used (let’s say) 10 car miles of fuel, vehicle depreciation, emissions, etc to go 5 miles.

If Suzy had driven, she would have gone directly to the shopping center, but parking would have added additional emissions. At most she would have spent 6 miles of fuel, depreciation, emissions, etc to go 5 miles.

But, let’s not forget that Suzy had to purchase her own personal transport vehicle (“car”). The construction (and eventual deconstruction) of her car carries a significant environmental expense that is very difficult to quantify. Although the fuel efficiency of the cab may be less due to the effects of cruising, by taking a taxi Suzy is using a vehicle that up to 30 other people have shared during a 12 hour shift. 30 less cars need to have been constructed if these people use a mix of taxi and public transportation as their primary mode of transit.

Should we ban cruising? No. Cruising is a necessary evil of cabs. In fact, it’s one of the desirable aspects of taxis — if you’re in a sketchy part of town, or just tired of waiting for a bus, a cruising taxi provides you with a valuable and essential service.

But, we can reduce cruising. The City has enforced taxi stands only at downtown hotels. A few taxi stands exist outside of the downtown area, such as the Castro, but they’re not enforced. That is to say, if I’m waiting at the 18/Castro taxi stand, other cabs can cruise the same block and pickup fares, even if they’re right across the street. There is no incentive (aside from the cost of gas) to remain stationary. I have a significantly higher chance of getting a fare if I’m cruising. If the City had an enforced taxi stand at 18/Castro, cabs would line up in an orderly fashion and wait for fares. It works in other cities around the world. But, don’t hold your breath. This is San Francisco, not a City of progress. I don’t think it’s likely this will happen.

Furthermore, at peak times this “cruising” to passenger ratio decreases significantly. If we decreased the number of taxis on the street during non-peak times this would significantly decrease overall cruising. (Yes, this is yet another argument for a variable supply of taxis on our City streets.)

And, sharing cabs starts to significantly increase its efficiency as a mode of transport. I can fit up to 6 people in the van cab, which I do more often than you may think.

The Green Cab company and the City (by issuing its alternative fuel medallions) are working toward a great end. Replacing our gas guzzling City taxi fleets with fuel saving models will make a measurable difference in fuel used and emissions. Keep up the good work.

But, taxis will never be a truly “green” mode of transportation.