20mph? It’s not that it’s too slow. It’s that it makes you feel like a Learner Driver again.

Alastair Somerville
2 min readSep 18, 2023

Shifting urban speed limits from 30mph to 20mph. There’s technical safety reasons why the shift is happening (to do with injury reduction) but people seem unwilling to take that factual advice and simply view it as government overreach and desire to control them.

It’s not the speed that matters to people

The thing which interests me is how much this is about messing around with unconscious (or is it subconscious?) skills. Drivers have trained their perception systems to judge 30mph. Very few people look at their speedometers repeatedly, they drive at the right speed because they can sense it and know it at a subconscious level.

Back to the future

Shifting from 30mph to 20mph means that the skill needs retraining. Suddenly people are driving and watching speed consciously. They’re thrown back in time to when they were learning. All that mixture of uncertainty, concern and hard attention. This is the emotional layer that causes so much stress and argument amongst people. Not the defined speed, not the facts about accident survival rates: it’s about people feeling emotionally uncomfortable.

Feeling like a silly kid again

Shifting learnt or socialised skills to conscious awareness can be very hard. The conscious mind is not terribly good at some things. It can be hard to concentrate, hard to learn and hard to control at the conscious layer.

Facing buried biases is hard

This is also why suddenly raising up unconscious biases (around historic issues like race and gender) can be hard. The conscious mind needs a lot of support to face, let alone change, knowledge and skills that were sunk many years ago into the unconscious or subconscious.



Alastair Somerville

Sensory Design Consultant, usability researcher and workshop facilitator. www.linkedin.com/in/alastair-somerville-b48b368 Twitter @acuity_design & @visceralUX