Gaining widespread driver compliance with 20 mph limits involves much more than relying on police enforcement. Multi-agency collaboration and social marketing are crucial.

The desired outcome is that drivers voluntarily slow down and respect a maximum of 20mph i.e. culture change. Even on isolated streets, if you simply alter speed limit signage from 30 to 20mph there follows a 2mph reduction in speed¹ (TRL Mackie 1998) and crashes by 10%² (Taylor et al. 2000). When implemented across a complete neighbourhood, falling maximum and average speeds bring additional important safety and quality of life gains. On faster roads self-enforced reductions in average speed can be as great as 7mph³ (Atkins 2010).

Reducing community street limits to 20mph is all about social behaviour change rather traffic engineering. Generally, 20mph limits should be self enforcing. Motorists must realise that streets are also where people live, shop or enjoy leisure. Most people agree that streets are not only for fast traffic. For mixed use streets, the message is 20’s plenty. Rather than just putting “signs on sticks”, successful limit schemes include so much more:-

• Engagement before road signs change. Instead of imposing limits, it’s best if residents are consulted and have opportunities to shape policy. The principle is as much about creating better places to live as reducing casualties.
• Community-wide 20mph limits apply to the vast majority of streets .e.g. 94% of Portsmouth. Most drivers therefore gain safety and amenity benefits in their neighbourhood. Exceptions to the default need justification so that the extent of limits makes sense.
• Single-phase implementation is ideal – e.g. Oxford. If this is unaffordable and 20mph roll out is progressive, then publically and continuously explain that most streets will be included over time.
• Extensive, sustained social marketing. A multi-agency approach with a budget of at least 10% of the capital installation costs is recommended for public engagement ⁴ (Toy 2012). Heavily selling and social marketing the benefits helps motorists to understand how and why 20mph improves safety, health and community life.
• Professional staff with expertise in soft measures including social marketing and internet viral campaigns.
• Community self policing e.g. drivers slowing down those behind, plus social disapproval of speeding, community speed watch programmes, reporting of speeder’s number plates, the loan of speed guns to activists etc.
• Occasional light touch enforcement with type-approved laser based detection equipment, 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 before (when enforcing a 30mph limit).

Top quality 20mph authorities e.g. Bristol and Liverpool have funds and expertise from Public Health. Liverpool’s “The 20 Effect” campaign has a logo, tagline, Face Book, Twitter, videos, celebrity endorsements, competitions and schools input. Plus branded products with high profile partners e.g. Police and Fire Services, Football clubs and more.

Public Health staff have experience and skill in promoting behaviour change. From April, Public Health is a local authority responsibility. Collaboration with transport planning, police and other agencies for better well being is key.

Crucially, good 20mph compliance needs a sustained, multi-agency marketing campaign. Integral is the requirement for the Police to play their role in creating the legal background. Occasional high profile warnings or fixed penalties will help. This need not divert resources from other police responsibilities.

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