Even on isolated streets simply altering signs from 30 to 20mph brings about a 2mph reduction in speed and crashes fall by 10%. When implemented widely, falling maximum and average speeds bring important quality of life gains. On faster roads self-enforced reductions in average speed can be 7mph.
As 20’sPlenty say, reducing community limits to 20mph is all about social behaviour change rather than traffic engineering. Generally, 20mph limits should be self enforcing. Motorists must realise that streets are also where people live, shop or enjoy leisure.
Rather than just putting “signs on sticks”, successful limit schemes include so much more:
- Engagement before road signs change
- Community-wide 20mph limits applying to the vast majority of streets - e.g. 94% of Portsmouth – so that most drivers gain benefits in their home neighbourhood. Exceptions need to be justified.
- Single-phase implementation - or, if roll out is progressive, there’s a need to publically and continuously explain that most streets will be included over time.
- Extensive, sustained social marketing. A multi-agency approach. Heavily selling the benefits helps motorists to understand how and why 20mph improves community life.
- Professional staff with expertise in soft measures including social marketing and internet viral campaigns.
- Community self policing slowing down those behind, social disapproval of speeding, community speed watch, reporting of speeder’s plates, loan of speed guns to activists.
- Occasional light touch enforcement warnings and Fixed Penalty Notices by traffic police. This is on top of extensive engagement. It is not an additional cost to the Police budget since there are the same number of roads and drivers as when enforcing a 30mph limit.
Full briefing with references.