More than 15 million people in the UK live in areas that have already adopted or are currently adopting speed limits. This data comes from the 20’s Plenty for Us, an organization in the UK dedicated to lowering speed limits for residential streets and facilitating pedestrian and cyclist safety. The organization now has more than 270 local campaigns in the UK and many major cities have committed to a 20mph (30kph) maximum speed limit on their streets.

The man behind this work is Rod King, founder and director of 20’s Plenty for Us. Mr. King was recently in Brazil, where the WRI Brasil Sustainable Cities team talked to him about working in British cities and the benefits of implementing safe speed limits.

Why is 20 mph (30 kph) ideal for road safety?

To put it simply, a default 20mph limit redefines the reference point for how we use and share the “public spaces between buildings” that we call streets. Instead of going faster and slowing down “only where required” we set a new standard for the residential places, where people live, where people shop, where people learn and where people shop of 30km/h, and then only go faster where streets and their use is compatible with the community’s wider needs for a liveable environment.

When you start off with the question “What is the right speed limit for the street outside your home” then you inevitably become part of the solution to better road safety when you recognize that we all must take a share in creating the conditions for our community streets.

And with regard to “road safety” the most important consideration is that in the 12m distance a 30km/h car can stop, a 50km/h car is still doing 38km/h. In addition when you drive slower you engage with pedestrians and cyclists much more and feel at one with the community rather than simply “driving through” the community.

You help empower people to change their own city. How does this process work?

Our approach is very much one of working with community campaigns to show how lower speeds can be of benefit and also empowering those community campaigns with the reasons and benefits of lower speeds. These enable them to demonstrate to politicians both the wide public support for lower speeds and the ability to make the changes in speed limit in accordance with that support.

We have a 9 point “roadmap” for local campaigns to follow (below). The key to this is that lower speeds are “community led – establishment endorsed.” We have to recognize that it is actually communities that we want to change their behavior, and if this is our goal then what better way to achieve that than starting with the community. But at the same time this is not simply an individual decision to drive more considerately but also an endorsement of a real change to the limit backed by the law.

Which cities are great examples today and why?

If you access our page of local campaigns, you will see all local authorities that have adopted 20 miles per hour with a “20 marker.” The other markers are blue, denoting cities where we have a campaign, and yellow for smaller villages or communities.

Cities with 20 miles per hour now include 75 percent of inner London boroughs. These are the districts in London (32 of them) that control the limits of most streets. It also includes the most iconic British cities and most of the top 40 authorities. Among them, Birmingham, Manchester, Bath, Bristol, Oxford, Cambridge, Liverpool, Edinburgh, Newcastle, Coventry, Brighton, York and whole municipalities, as Lancashire.

British cities and Brazilian cities are different for historical and cultural reasons. But best practices show that we have a recipe to save lives. Do you agree?

The key to understanding cities is an understanding of the needs of their communities. And while there are undoubtedly cultural, economic and historic differences between such places as London and Sao Paulo it is a fact that we all share common values about what we want for our families and communities. We want our children to be able to use our roads independently, we want the elderly to be able to maintain their mobility and we want an environment with lower noise and emission pollution. These are common and by discussing these needs and how fast traffic endangers such objectives then we can all come to the conclusion that a 20mph place is a better place to be. And that is why such limits are being so widely embraced throughout Europe and North America where 30kph or 20mph limits are becoming the norm for residential streets in our cities and those where people walk and cycle.

The best practice we would say is to go through the “roadmap” and do a lot of engagement. And I really do believe that Sao Paulo has a great opportunity to become an even better city. Most important will be the de-coupling of the general speed reduction issues on the freeways from the idea of setting the right limits for where people live—where they and their family get such a great benefit. Of course we advise starting some “Love 30” campaigns around the city in communities to start to show the support for lower speeds on residential streets.

Do you have an estimate of how many lives you have saved since the beginning of 20’s Plenty for Us?

Sadly, or perhaps encouragingly, nobody records near misses. But we do know that reducing speeds makes for fewer casualties. Often we hear a report of “boy breaks arm when hit by a car in a 20mph limit”. These are quite satisfying because it’s far better than a report of “a boy dies in a 30mph limit.”

This interview originally appeared on TheCityFix Brasil in Portuguese.