Is your car faster than your bicycle?

I read a book many years ago by Henry Thoreau about a low energy lifestyle. In it he laughs at the person who spends much of their time saving to buy a ticket to go to the beach. He laughs because if that person had just started walking to the beach he would have arrived sooner. His story illustrates a simple idea which I was reminded of by Frank Fisher in his recent letter to the economics Age.

The idea is that when we work out how fast our commuting vehicle travels, be it car, bike, bus or helicopter, we need to not only measure the speed of the vehicle averaged over the trip, but averaged over the time it takes to recap the cost of the trip. When people suggest that riding a bike to work would be too slow, I sometimes offer that they instead fly a jet helicopter - much quicker, and you can park on the roof too!

At that point most people (there are some thick or perverse people out there) realise that you must include the cost of the trip in your total time. Last time I had a helicopter trip it cost $300 per person per hour. If I used that for my daily commute I'd never earn any money.

So Thoreau, then Illich, Tranter12 and Fisher suggest that we compute not the average speed of the trip, but the effective speed of our transport. For each person, and for each vehicle, the effective speed will be different, but there are some basic factors which we can use to get a ballpark figure.

In this little javascript program, I compute the annual cost for the car and use it and the travel time to compute a total annual time. Dividing this into the car's annual distance travelled (You can either give 1 year, or if you've always owned the car, the total and the age of the car). This gives the effective speed of the car.

This is still very rough and I'm very happy for people to send corrections or suggestions. I am only considering car travel. Perhaps I'll write one for public transport and bike transport later if I get enthused.

Public transport is probably the easiest to estimate - work out your trip time, add the time it takes to earn the fare and divide into the trip distance.

Bike time is a little harder because bike riding does increase appetite a little, and does require rare maintenance. (However, it does reduce fitness club membership bills :)

I am depreciating the car's cost as total cost/10 years. This is rough, I'm interested if someone has a better idea. Quag suggested How much of your car should you finance? as a starting point. RACV also give depreciation rates for most models.

Also worth a good read is the late Ken Kifer's bike page on Auto Costs Versus Bike Costs (He also mentioned Thoreau's book)

Have fun!

First, let's compute the distance travelled each year. You can either record the odometer value or the distance travelled in the last year: km. If this is for one year, set the years for odometer, to 1, otherwise use the age of the car.

We're going to approximate the depreciation assuming the car loses all its value in 10 years. This is certainly wrong, but a reasonable rough guess. Car price $

Next, we need to estimate fuel expenses using the petrol per week: liters * $/litre.

To put a value on our time we'll assume you work 47 weeks each year. Your annual income (note that this program runs on your computer, I never see anything from it), $ and hours per week working, hours. But you have to pay taxes, only % is yours after tax.

How long do you actually spend traveling? Remember to include the time getting you car out of the garage, finding a park and walking to your office. Minutes per week driving minutes per day * days working. You probably use the car for things other than driving to work, add any extra time spent each week driving to the shops or your mum's for dinner: hours.

Don't forget your insurance per year, $, and the car registration per year, $.

So, you traveled over the last year. You spent ... hours actually travelling, but also spent $... paying for your car. If money is time then your time is worth $.../hour. We're using time worked only, in fact we should really include recuperating time at home.

Given your time value, the extra costs are costing you an extra time of ... hours/year. This brings the total time spent doing car related stuff to ... hours/year.

Your car's effective speed is