[olduser]

I noticed this on BBC News:
https://www.bbc.co.uk/news/articles/c70j0gv5xpdo

What they forget is it takes time for the novelty to wear off.
Driving at 20 MPH is novel for the driver and pedestrians, they both have to adjust to new timings.
For the driver, how long before I arrive at a point?
For the pedestrian, how long before the vehicle arrives here?
They will both overestimate at first, causing them to stay well apart, resulting in a low number of conflicts.
Once they have got accustomed to the new timings, they will exploit them restoring the high number of conflict as before.

While the speed limit is novel for the driver, he/she will be paying attention because they are uncomfortable but once they are comfortable with the new speed, attention will waver once again.

I think almost any change will have a similar result.

[Marc]

Welcome to the community @olduser and thanks for sharing this 😀
I see what you mean, we become less careful over time?
Doesn't that perspective mean, therefore, that the actual speed limit is irrelevant?

[olduser]

Hi Marc,
My conclusions after a lifetime of driving are:
We tend to drive harder, flirting with risk until we frighten ourselves we then level off at that.
We are creatures of habit.

The first statement as some inbuilt traps, to be frightened I think you need imagination, to be able to imagine what might have happened, the other trap I think applies to young men, if there are others in the vehicle at the time, it is difficult to admit to the others, and yourself you were frightened.

More relevant to the 20 MPH but does include the fright factor.
Until 20 MPH becomes habit, it is a novelty we have to actively think about driving, because our 30 MPH habits applied at 20 MPH will not produce the 'normal' level of fear or stress, it takes time to adjust for this.
When the new speed gets to be a habit, we start to raise the fright/stress level back up as it was previously, what ever distance we braked for 30 we now shorten and so on.
The same goes for pedestrians, they will learn to cross the road with a car nearer, because they can the car is slower, until they feel the old amount of fear or stress.

I think, these changes are at a subconscious or habit level, so we don't notice but what we have done is raise the risk of accidents back to it's old level, the lower speed may, in some cases, reduce the amount of damage but it is still damage, and traumatic for all involved.

Changes, any changes, will tend to produce a drop in incidents but once the novelty has worn off the incident rate will creep back to it's old level.

As to a 20 MPH limit as such:
Modern cars are developed with 30 MPH as the lowest comfortable speed (the engine/transmission mechanically is in it's comfortable range) and pollution is low, dropping to 20 is too low.

Speed limits in themselves take the responsibility away from the driver, I know this is not what is intended but this is the effect.
If there is a crash, you always here, "I was within the speed limit" and "was the driver going faster then the limit?"
The first implying it was not my fault, and the second over the limit it must be your fault.
Where the real question is, "which party made the wrong choice, and why?"

Another unintended result of speed limits, they create a culture of driving at the speed limit, even learners get failed for not driving at the limit!
Yet experience tells us there are times when 5 MPH is the safe speed but if I am taught to drive at the limit what to do?

[Rolebama]

I sometimes used to travel through St Albans town centre. 20mph limit past a taxi rank.I now go around the town centre because of too many near misses with the cabs pulling straight out. Harefield and Wheathampstead have 20 limits through their town centres but it seems most drivers ignore them, so others don't pull out in front. (Hope that makes sense.)