A Year of Change
“We’ve now got a complete year of data,” said Phil Jones. “From October 2023 to September 2024, we’ve seen a 28% reduction in all recorded casualties on roads where the speed limit changed from 30 to 20mph. That’s 677 fewer people injured—about 1.9 people per day.”

The reduction spans all severities, including 10 fewer fatalities and 95 fewer serious injuries. “It’s in line with expectations,” Jones added. “There were concerns that lower speed limits wouldn’t reduce casualties, but the evidence shows otherwise.”

The Physics of Safety
Kate Carpenter explained why even small reductions in speed can have a big impact. “Inertia is a function of the square of velocity,” she said. “So a small drop in speed leads to a disproportionately large reduction in injury severity.”

She added that lower speeds also give drivers more time to react, reducing the likelihood of collisions in the first place. “It’s not just about physics—it’s about human behaviour. People drive more smoothly, they’re less stressed, and they’re more likely to notice pedestrians or cyclists.”

Public Perception and Behaviour
Despite initial resistance, Kate Carpenter believes public attitudes are shifting. “People are on a journey. At first, they thought it would massively increase journey times. But they’ve realised that’s not the case. You’re not driving at 30mph all the time—you’re accelerating and decelerating. The actual impact on journey time is minimal.”

Phil Jones agreed, noting that the widespread nature of the change helped. “When you change a big area—like most of the urban road network in Wales—it’s hard to ignore. People may not agree with it, but they know it’s there. And once they know it’s there, they tend to slow down.”

Communication Lessons
Both guests acknowledged that the rollout could have been communicated better. “We weren’t as smart as we should have been,” said Kate Carpenter. “We need to talk to people before we implement changes, not after.”

Phil Jones added, “COVID didn’t help. A lot of the preparation happened during the pandemic, and there wasn’t enough engagement with the public. In some areas, people didn’t believe it would actually happen—until it did.”

Political Courage
Phil Jones praised the political leadership behind the policy, particularly former Deputy Minister for Climate Change Lee Waters. “Someone asked him how much political capital he burned on this. He said, ‘All of it.’ But that’s what he was there for. He wasn’t a career politician—he was there to do things.”

A Broader Ethical Case
Kate Carpenter framed the issue as an ethical one. “It’s quite unethical not to do this when it’s a low-cost, large-scale benefit to the public. It reduces injuries, improves air quality, lowers insurance premiums, and even reduces road maintenance costs.”

She cited data from insurer esure, which reported a 20% reduction in claims and £50 lower premiums in Wales compared to similar areas in England. “Insurers are data-led. They don’t care about politics—they care about risk. And the data shows this works.”

Lessons for England and Beyond
Phil Jones called for a review of England’s speed limit guidance, which currently discourages 20mph limits unless average speeds are already low. “That’s perverse,” he said. “If speeds are high, that’s where you get the biggest benefit from reducing them.”

Kate Carpenter agreed, urging the UK government to show leadership. “Wales has shown that large-area implementation works. Local authorities in England want to do the same, but they need national support.”

The Bigger Picture
Both guests emphasised that speed management should be a key part of the UK’s upcoming road safety strategy. “It hits virtually every political priority,” said Kate Carpenter. “Health, well-being, congestion, emissions—it’s all connected.”

Phil Jones added that transport remains the UK’s largest source of carbon emissions. “We’ve decarbonised the grid and improved home efficiency, but we’re not doing enough on transport. Speed management is a simple, effective step.”

Final Thoughts
As the data continues to roll in, the case for 20mph speed limits grows stronger. “We’re seeing consistent findings over large areas and long periods,” said Kate Carpenter. “It’s a low-cost way to achieve big benefits.”

Phil Jones concluded, “The burden of proof has shifted. We now need good reasons not to implement 20mph limits in urban areas. It’s no longer about why we should—it’s about why we wouldn’t.”

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