The explanation and example of "Social Speed" given below is taken from David Engwicht's book titled Street Reclaiming- Creating Livable Streets and Vibrant Communities (pp. 65-66)
"The first of the 5R’s of Traffic Reduction is to replace some trips with walking, cycling, or using public transport.
In the past, many people have seen using these modes of transport, particularly walking and cycling, as slow and inefficient compared to driving a car. But are they?
Traditionally, the only time considered when comparing the speed of walking or cycling to driving the car is the actual time spent travelling. But this ignores two other important time costs, the first being the time spent earning the money to pay the costs of buying, maintaining, and running the car. Seifried (quoted in Whitelegg) coined the term "social speed" to give some idea of the average speed of different modes of transport once these hidden time costs are taken into account. Whitelegg Writes:
According to Seifried, the social speed of a typical bicycle is 14 kilometres per hour (kph), only three kph slower than that of a small car. If other external costs (air and noise pollution, accident costs, road construction costs and so on) are taken into account as well, then the small car is one kph slower than the bicycle.
Studies show that people have a travel time budget. Average journey-to-work times have remained around the 20-30 minute mark since the times when most people walked to work (Manning, p.42). This phenomenon has caused Whitelegg to refer to a "time illusion’ which results in "a theft of time." For example, compare a car owner who spends 30 minutes per day driving 20 kilometres to work with a bicyclist who spends the same time covering seven and a half kilometres. Car owners will feel that they are travelling faster. But in reality, when all the time costs are factored in, they are spending 70 minutes to cover the distance while the cyclist is spending only 32 minutes.
But perhaps the greatest time cost that is not factored in (and one not included in the social speed examples above) is time lost through health impacts. Let me illustrate this with a personal story. At age 44 I went to my doctor for a health check to find that my blood pressure was unacceptably high. He went to his bookshelves and pulled out some research that showed that at my age, and with my level of blood pressure, I would lose 18 years off my life. He then informed me that all I needed to bring my blood pressure down was 20 minutes exercise each day — which could be as simple as a brisk walk. By walking to work I could save 18 years."