Even with the caveats about limited data and untangling causation and correlation, the statistics are striking: the first year of a scheme in Wales where the speed limit on urban roads was lowered to 20mph resulted in about 100 fewer people killed or seriously injured.
If these drivers don’t obey the rules now, what makes you think they will obey them if you lower the speed limit?
And you don’t just lose control of your car at 30mph or even 50. Especially not in today’s cars with all their safety features.
They don’t have to lose full control. They could be following too closely and swerve onto the sidewalk to avoid a collision with a car and end up striking a pedestrian.
Speeders will stick out even more making them easier to spot in traffic. The reduced speed limit should also be accompanied by lane narrowing, speed humps, and other traffic calming techniques.
This is a matter of the human factor - and you can never make that disappear. There will always be the odd idiot driver.
This is totally fine for housing areas, but definitely not for through-roads. There’s no one-for-all solution in the same way our bodies don’t have only one size of blood vessel.
The reduced speed limit should come with traffic calming relative to the speed limit. If a through road has a 20 MPH zone that area should have lane narrowing and at least raised crossings.