After returning from New York last Monday, I’ve been met by a barrage of 20mph signs around Oxford. Most roads in the city centre have been limited to 20mph. As both a cyclist and driver, what are the costs and benefits of this decision?
Benefits of 20mph Zones
- Slower speed of cars will make cycling more enjoyable and less dangerous. At lower speed, accidents are less likely and also less likely to be fatal. At 30mph, 50% of collisions prove fatal, at 20mph, the fatality rate is only 10%
- Slower speed and greater safety may encourage more people to cycle and walk. This creates a critical mass of less cars on the road.
- Lower number of cars on the road will help reduce pollution and create a better environment.
Costs of 20mph
- Slower journey times for drivers.
- More petrol consumption, 20mph is less efficient than 30mph. More petrol is consumed at this lower speed.
- Chance of increased congestion. Lower speeds mean slower moving traffic and possibly more traffic jams. Though, if the lower speeds deter cars, congestion could improve.
- The main issue is will the 20mph speed limit be enforced? It is one thing to put a sign saying 20mph, but do drivers may any attention unless there are speed cameras? I have still seen cars speeding past at 40mph.
- Note: the costs to the drivers are mainly private costs – increased time, increased petrol consumption. Many benefits are external benefits e.g. less chance of fatal accidents to other people.
- The real beneficiaries are those who cycle, walk and have children who like to play in the road. Car drivers are the least to benefit with facing longer journey times. However, the extra journey time is fairly marginal as many of the roads limited to 20mph are not fit for fast speeds anyway.
- If 20mph speed limits do lead to lower fatalities that is a pretty big benefit. If we assign a value of life saved at £2million, then the potential benefits are significant.
- As a cyclist I’m very happy, to have 20mph speed limits, as a driver I have to admit I’m not used to driving at 20mph. But, I’d be quite happy if they introduced speed cameras to enforce it.
See also: Benefits of 20 mph zone