In 1975, in his book *Energy and Equity*, Ivan Illich defined the concept of generalized speed. To calculate the speed of a journey, he proposed to count not only the time it takes to travel a certain distance but also the time spent in providing the means of travel. Taking the data of the time, Illich noted: » *The typical American spends more than 1,500 hours a year (or 30 hours a week, or 4 hours a day, including Sundays) on his or her car: this includes the hours he or she spends behind the wheel, both on and off the road; the hours of work needed to pay for it and to pay for gas, tires, tolls, insurance, tickets and taxes… For this American, it takes 1,500 hours to drive (in a year) 10,000 km, or an average speed of 6km/h. In countries without a transport industry, people move at exactly the same speed by walking, with the added advantage that they can go anywhere, not just along paved roads *« . Illich, extending his logic of counter-productivity to the field of mobility, thus shows that, when a certain optimum is exceeded, we regress. He concludes: » *A man on foot covers as many kilometers in an hour of transportation as a man with a motor, but he spends five to ten times less time on his travels than the latter. Moral: the more a company distributes these fast vehicles, the more, beyond a certain threshold, people spend and waste time moving around in them *« .

Since then, this ingenious idea has given rise to many developments, has been translated into magnificent mathematical formulas and graphs^{(1)} and has provoked economic debates that we will spare you here; we will update the subject by emphasizing the social implications of this reasoning.

Let’s assume two commuters with different social status who have to travel 2 times 50km to and from work. The physical speed of each of them is identical: they take one hour in the morning and one hour in the evening for their travels (we are reasonably optimistic, there are not too many accidents, not too many works, no bridges or tunnels closed because of dilapidation, so not too many traffic jams). They therefore moved at a physical speed of 50km/h. But, for this trip, they spent a certain amount of money and therefore had to work a certain amount of time in the job (job, job…) of their day. Illich’s brilliant idea is therefore to add the time spent working to make the journey possible to the time of the shuttle to measure its real speed.

Jules Dupont is a laborer in a small business and earns 10€ an hour. With his old Twingo, he has a cost per kilometer of 20 cents^{(2)}. His daily 100km trip costs him 20€ and he has to spend 2 of his 8 hours of work per day to finance it.

Pierre-Henri de la Barrière Qui Claque is CEO of the multinational *Bigmoney*. His BMW 7 series costs him 98 cents per kilometer^{(3)} and his 100km journey costs him 98€. His annual salary being 1 million € for the 1,300 hours spent at the Board of Directors and in his offices, we can calculate that he earns 769€ per hour. It must therefore devote 98/769,
12.7% of an hour (or 7 minutes) to pay for his
commute to and from work.

Let’s calculate the generalized speed of our two friends. Jules spends 3 hours making and financing her 100km trip, which is a generalized speed of 33.3km/h (100/3). Pierre-Henri, on the other hand, covers his 100km by spending 1h07, thus reaching a generalized speed of 88km/h (100/1,127), for the same journey…

This notion of generalized speed has given rise to much controversy. Some calculated that a cyclist was going faster than a motorist in a built-up area, others estimated that it was about the same, but it was always between 5 and 15km/h, which is the speed of a stagecoach from 2 centuries ago. But what is certain, as our example above shows, is that there is quite a difference depending on your social status and income. The moral of what is not a fable is therefore » *Depending on whether you are powerful or miserable, your movements will be fast or slow *« ^{(4)}.

**Alain Adriaens
**

- Pour les scientifiques, par exemple : Frédéric Héran, À propos de la vitesse généralisée des transports. Un concept d’Ibvan Illich revisité, Cairn info, 2009, https://www.cairn.info/revue-d-economie-regionale-et-urbaine-2009–3‑page-449.htm
- Calculé grâce au calculateur du prix de revient du Moniteur de l’automobile: https://www.moniteurautomobile.be/conseils-financiers/prix-de-revient-au-km-par-mois.html
- Voir note 2.
- Comme le titre de cet article, librement inspiré de Jean de la Fontaine, Le lièvre et la tortue et Les animaux malades de la peste.