20’s Plenty for Us campaign for community-wide 20mph limits and separated, high quality infrastructure where higher vehicle speeds are justified. Infrastructure costs are due to letting drivers travel at speeds where interactions between cyclist and motor vehicles are unsafe. The cost of infrastructure is largely the cost of driving at speed and are not costs of cycling and walking.
Politicians and professionals realise utility cycling (i.e. to work, shops, school) reaps massive benefits - easing congestion, traffic reduction, school run issues, relieving parking problems, improved air quality, raised public health, physical activity levels and more. Yet the British Social Attitudes Survey finds only 5% of people cycle at least weekly. What’s the most cost effective way to make a step change to increase utility cycling? Good evidence from places with wide 20mph limits confirms that lowering speed limits gives most returns per pound spent.
Traffic speed and volumes inversely relate to walking and cycling levels. The World Health Organisation say 20mph is the maximum safe speed where there might be conflicts between cars and cyclists. Safety fears are what people say most puts them off cycling. Cycling casualty rates fall 20-40% with wide area 20mph limits.
Making side streets 20mph has raised cycling levels. Cycling to school trebled in the Edinburgh 20mph South Central trial. A key to maximizing utility cycling gains is to set 20mph limits or separated infrastructure along desire line routes, i.e the direct routes. Space is most easily found for off-road cycling on quiet routes - eg old railways or river paths. Yet, the next tranche of those who might be willing to cycle more may not find indirect paths enticing due to being in a hurry and wanting to minimise journey time.
For traffic engineers the key to fitting in separated cycle infrastructure is finding available land alongside highways or enough carriageway for lanes of a least 1.5m wide (2m is recommended). Yet, what if there isn’t space for a joined up safe separated cycle network? The choice becomes introduce 20mph limits or reduce parking or driving lanes (ie reduce motor vehicle road space). Separated lanes for cyclists and 20mph limits both have their place.
Wide 20mph limits are popular, easy to do, quick and cheap to install once there is political will. They are also great value for money with minimal signage requirements costing only about £1.50 per head of population. Many funding streams can be used and wide area 20mph will always beat small scale schemes in cost effectiveness as they benefit the many. For a city of 200,000 people 20mph limits is only £300k. We recommend that authorities use public health experts for driver education, engagement and gain police agreement to at least minimal enforcement, with an optimal spend of £2-3 per head.
Residential 20mph limits without humps have 70% approval. Popularity rises once installed. 20mph limits raise cycle rates for a minimal cost per additional trip. Note that the costs of cycle infrastructure are not due to cycling and walking, but come from allowing faster than 20mph driving. If drivers are permitted to go faster, then protection for vulnerable road users is required with off road or separated provision for their public health protection.