International research confirms that reducing speed limits in urban areas saves lives
Our cities are undergoing a speed revolution, but it might not look the way you expect. Across the globe, urban areas are choosing to reduce the speeds with which vehicles move through their streets.
To date, close to 200 cities in France have introduced a 30 km/h speed limit – a trend being echoed in numerous other European countries. In the US, cities like Seattle, Minneapolis, Portland and Washington DC have all reduced speeds on their urban roads in recent years. As of this year, in London, 355km (220 miles) of roads now have a 20 mph (32 km/h) limit; up from 215km in in 2022. Sydney and Melbourne are also implementing lower speeds on their central city and suburban roads.
So, why are so many cities choosing to reduce speed limits on their roads?
The biggest and most obvious reason is safety.
Kinetic energy
City streets aren’t the sole domain of cars and their drivers. They’re also home to pedestrians of all ages, to cyclists, mobility scooter and wheelchair users, to groups of playing children, and mass transit passengers. They are shared spaces, which means they need to provide safety to all.
The higher the speed a vehicle travels, the greater the risk of serious injury or death – especially to those outside a car – if there is a crash. It all comes down to basic physics. The energy a moving object has – its kinetic energy – is dependent on the mass of that object, and its velocity (the speed at which its traveling). Of these two factors, velocity is the dominant one, because energy increases with the velocity squared. That means even a very small increase in speed leads to a huge increase in the kinetic energy.
The same car traveling at 50 km/h has almost three times as much kinetic energy as it has at 30 km/h*. In the case of a crash, that means almost three times the destructive potential. As a result, a pedestrian hit by a car traveling at 50km/h has a 90% chance of dying. At 30km/h, a pedestrian has a 90% chance of survival (or a 10% chance of dying).
Higher speeds also give drivers and other road users less time to react to an emergency, and it increases vehicle stopping distance. Speed was a factor in almost half of fatal collisions in London in 2022. And a recent study combining data sources indicates that speeding is involved in around 60% of fatal crashes here in Aotearoa New Zealand.
There is a lot of research into the link between vehicle speed and crash risks, including this 2018 study from the OECD and the International Transport Forum (ITF). All largely show the same thing – the higher the average vehicle speed, the higher the number of crashes and casualties. In looking across data from 10 countries, the OECD/ITF analysis found zero examples of increasing speeds leading to better safety outcomes. Is it any wonder that cities are trying to slow vehicles down?
Benefits beyond safety
Just a few weeks ago, Professor George Yannis and PhD candidate Eva Michelaraki – both researchers at the National Technical University of Athens – published a comprehensive, large-scale review into the various impacts that reducing speed limits have had in European cities. Writing in the (open-access) journal Sustainability, they looked at studies of 40 cities who’ve adopted 30 km/h speed limits in at least some of their neighborhoods, and noted any changes in factors like safety, environmental impact, traffic, and livability that resulted from those lower speed limits.
The studied cities included large ones like London, Barcelona and Berlin, alongside smaller ones, like Montpellier and Bologna. Some implemented lower speed limits three decades ago, while others did so more recently. In addition, available data varied from city to city, as did the stated reason for making changes to their speed limits. But when viewed together, the results paint a very clear picture, particularly of the safety benefits that come with slower speeds.
Yannis and Michelaraki found that, on average, the introduction of 30 km/h speed limits in these European cities resulted in a:
· 23% reduction in road crashes
· 37% reduction in fatalities
· 38% reduction in injuries.
As averages, these figures don’t tell the full story of any one city, but as an example, Münster (a city in western Germany) introduced city-wide 30 km/h speed limits in July 2021. One year later, there was a 72% decrease in the number of people severely injured in road crashes.
The Athens study measured benefits beyond safety too. For example, air pollutants including nitrogen dioxide (NO2) and particulate matter (PM) were seen drop by an average of 18%, and noise pollution was reduced too. High prevalence of these pollutants has been linked to asthma, cardiovascular conditions, and even stroke risk.
The study also looked at one of the common criticisms leveled at lower speed limits – that drivers will experience longer journey times a result. Across all of the cities included in the paper, the authors found that travel times did increase. But the increase was small, between 3% and 5%. On a 40-minute drive through a city, that would equate to spending an extra 72 seconds to 2 minutes in the car.
This should come as no surprise to anyone who regularly drives in urban and metropolitan areas. The presence of traffic lights, congestion, intersections and pedestrian crossings mean that you spend a lot of time traveling at 0 km/h, and might only ever travel at or near the speed limit for small portions of your journey.
The impact on traffic flow was a bit more mixed – in some instances, lower speeds led to slightly more congestion, but on average, congestion was reduced by 2%.
And finally, in those cities that reduced their speed limits, there was an increased uptake of active transit – cycling and walking. This suggests that making streets slower and safer enabled some people to leave their car at home.
Going the wrong way
Given the overwhelming benefits of reducing speed limits in urban areas, you’d probably be surprised to hear of places choosing to instead increase speed limits. Well, that is what’s being proposed here in New Zealand.
Minister of Transport, Simeon Brown, pledged to “reverse Labour’s blanket speed limit reductions”, saying that “Returning roads to their previous speed limits will enable Kiwis and freight to get to where they need to go, quickly and safely.”
“I don’t think there’s any way Simeon Brown could put his hand up and say, this is evidence-based policy,” says Professor Simon Kingham. “He continually talks about the previous government’s blanket speed reductions. In reality, they were targeted and underwent full consultation. The only blanket speed changes are what he’s proposing. And that’s a blanket speed limit increase.”
Kingham, a geographer from the University of Canterbury, whose research primarily focuses on the impact of the urban environment on health and wellbeing, has been a vocal opponent to this proposal in recent months. And he’s in a unique position to comment on it. For more than six years until the end of May 2024, he had been seconded to the Ministry of Transport as their Chief Science Advisor. He ended up leaving the post earlier than planned after being “encouraged to go” by the Ministry, who, he says, “didn’t want science anymore.”
“There’s an irony there,” says Kingham. “If I hadn’t left two months early, I would not have been able to say anything at the moment.” Since leaving, he’s spoken to the media, written articles on the topic, and co-authored a briefing for the Public Health Communication Centre with Dr Angela Curl.
Brown’s argument for increasing speed limits is that it will improve “productivity” by decreasing travel times, but as Kingham explains, “research on this is unclear. Any benefits are based on the assumption that people use time savings to be more productive, which they often don’t.”
In contrast, the evidence that higher speed limits lead to worse health outcomes is overwhelming.
A 2016 study found that anthropogenic (human-made) air pollution was responsible for approximately 3,300 premature deaths per year here in NZ, and social costs of $15.6 billion per year. This, says Kingham, is being ignored by Brown, “NZ’s Emissions Trading Scheme (ETS) is our primary tool for reducing emissions, but it only talks about greenhouse gases. It ignores other emissions and the people impacted by them. You can’t ‘offset’ people dying from inhaling nitrogen dioxide and particulates.”
Public consultation on the speed limit proposal closed last week. At the time of writing, the government had yet to make any comment on the next stages.
Kingham says he has “a little bit of hope” that Minister Brown might reconsider his course of action, in response to not only international evidence, but also the content of the submissions (which included this one from The New Zealand College of Public Health Medicine), and the opinions of the NZ public. But he’s not holding his breath, saying “he [Brown] doesn’t seem to be very good listener, does he?”
Introducing lower speed limits hasn’t always been a popular choice. When Graz, Austria first announced a reduction from 50 to 30 km/h back in 1992, less than a third of residents were in support of the move. A few months after the change, approvals had risen to 52%. And several years after that, it reached 81%. In almost every case where a city has introduced 30km/h areas, the benefits were so significant and happened so quickly, that those limits were later expanded out to more areas.
To finish, I’ll leave you with a quote from a recent Not Just Bikes video, because it’s a pretty succinct summary of my opinion: “At some point, we have to realize that anybody fighting against lower speed limits in cities is either willfully ignorant, or they’re a selfish a**hole who values their convenience more than other people’s safety.”
* Based on a vehicle weighing 2000 kg. Kinetic energy at 30 km/h (or 8.33 m/s) = 69,389 J. Kinetic energy at 50 km/h (or 13.89m/s) = 192,932 J, or 2.8 times higher.
