20mph speed limit rollout by Lewisham Council (effective September 2016)


I’m not going to look for better data, but the obvious questions about this stat are:

  • how many accidents there were in each zone? (so we can avoid making inferences based on a small sample)
  • were the accidents in the 20mph zone less severe? (one of the major arguments for 20mph vs 30mph)

The article also argues that the new speed limit has had marginal impact on speeds. If this is true then why should we expect anything more than a marginal impact on accidents anyway?

Not having useful data available does not mean we should infer things from useless data.


Irrespective of the arguments for and again the 20 mph speed limit, I love this statement more than I can say. I think it should be engraved at the top of any screen with internet access.


Good questions, both of which Manchester Council must have considered before choosing to halt the rollout of 20 mph limits.

As I’ve argued elsewhere:

  • The confusion of non-standard limits means driver attention is diverted from pedestrians and other road users - instead, drivers are looking out for signage, speed bumps and cameras.
  • Introducing unsuitable blanket limits led the police to de-prioritise enforcement (as shown in posts above). A lack of enforcement will worsen a spectrum of dangerous driving behaviours (of which speed is only one).
  • Disparate driving styles on already dangerous urban roads. A handful of drivers doggedly stick to 20 mph limits, and everyone else is frustrated and delayed behind them. This leads to dangerous overtaking, rising levels of driver anger (just human nature) and awkward confluences of 20 mph and
    30 mph zones.


I can imagine there is some truth to your 1st and 3rd bullets but I haven’t read that enforcement of 30mph has been de-prioritised and can’t see how de-prioritising 20mph enforcement would lead to worse behaviours than under a 30mph limit.

And of course your arguments need to be weighed up against the argument that many drivers will now drive more slowly and this will reduce the incidence and severity of accidents.


You asked why 20mph zones might see increased accident rates - I mentioned police enforcement because the police chief guidance clearly de-prioritises enforcement within 20mph zones due to the inappropriate limits. Reduced enforcement will lead to more dangerous driving behaviour.

I wasn’t talking about enforcement within 30mph limits.


Are you referring to the ACPO guidance article you posted?

I took the article to mean that they will chose when to enforce the new 20mph limits, but not that this would mean enforcement becoming more relaxed than pre Sep-2016 (even in ‘20mph zones’).

If someone could put together a list of which SE23 roads “feel and look like a 20mph zone rather than a zone with a 30mph or higher limit” I’m sure many of us would find it useful.




I see your interpretation, but don’t believe that they are suggesting only enforcing any kind of driving standards “where the limit is obvious to drivers”


Seems the 20mph blight continues to spread to other boroughs. Quite irritating when switching from one borough to another, where the neighbouring borough doesn’t need to post obvious speed signs as mentioned above, 30 is the assumed limit.
Lovely to see places like Perry Vale where the average hasn’t dropped, embellished with “Thank you for driving safely” signs. More money, thanking people for nothing. Well done Lewisham.

Still seems to me like more thought is needed on these zones. Especially when the speed activated matrix on Brockley Road STILL flashes up with 30mph in the middle of a 20mph.

Can’t wait for the next phase to start, the traffic calming measures. Thank heavens for cycling.


Cannot wait for 20mph in Forest hill. It scares the life out of me when lorries turn on South Circular road to the left, opposite the WHSmith on high spreed. Sometimes i step back hoping it may save me if a lorry flips over, but of course there are hardly any chances of survival if happens that a lorry looses control and flips over. Some drivers are mad, not all of them, very few of them but because of those few people have to suffer.


That is a Red Route and will remain 30mph. The rest of Forest Hill other than the red routes are already 20mph.


Shame, why do people need 20mph on quiet roads when cars are driven like mad on the main roads where most accidents happen?


Main roads are for the movement of the majority of traffic volumes, smaller roads are mainly residential where people cross and children play.
The borough is already slowing down badly due to the borough wide 20mph, especially on more major roads. The last thing it needs is to be even slower.

The speed of large vehicles is always exaggerated by perception due to their large size and close proximity. I’m pretty sure most lorries are not doing much more than 20 around that corner.


Slowing traffic down or people’s lifes and safety…hm…what a choice.


If safety was the only concern worth considering, cars would be banned altogether. As would people walking on pavements without knee pads and elbow pads. This is about finding a sensible compromise that allows commerce and travel to continue whilst factoring in reasonable safety measures.


Far from it. I think that dangerous parts of the roads should have 20mph speed limit, like the one opposite WHSmith. No need to lower the speed limit everywhere, it will be silly. City and town roads are not motorways at the end of the day and drivers should be careful and considered when driving.


Some parts of roads, like the one you suggest, have naturally imposed speed limits, being the maximum speed it is possible to navigate the corner. As I say, larger vehicles are unlikely to occur exceed 20 due to the angle of the corner.

Speed is not a killer, the vehicle is, and the manner in which it is driven. Speed and stupidity are not the same thing. Sadly the latter is the the largest contributor to accidents.

While other countries raise and lower speed limits at what seems like 100 metre segments at a time, this is both costly and impractical. Of course lives matter. Given the footfall on that piece of road vs accidents, I would say it’s a pretty safe spot. Except for when idiots refuse to wait for the lights to change, or commuters play chicken 20ft from the crossing.

TfL do actually have a few sections of their RR which is 20mph, New Cross for one, but I get the impression that it is not an ideal at all.

While I despise the borough wide roll out of this limit, I can appreciate it is needed in some spots. The danger now is those too impatient to drive at that speed, recklessly over taking.

If any reconsideration is to be had, I would say it was to UP the speed limit back to 30 on certain roads, such as Brockley Rise through to Lewisham Way for example. Sadly I don’t think their assessment and adapt phase has this in mind for a second.


Here’s a local poll by NewsShopper:

Curiously Lewisham Council aren’t publicly publishing the results of their consultation on 20mph limits in Forest Hill… :thinking:


not exactly persuaded by that. Is that the NewsShopper known nationally for its authoritative research studies or perhaps a different one? Agree it would be interesting to see local consultation outcomes but wonder how representative of wider opinion it would be. I’ll drop that national study here so we can see it on this thread. http://www.bristolhealthpartners.org.uk/latest-news/2017/10/16/public-support-for-20mph-limits-holds-firm-new-study-reveals/961


“However, approximately half of those surveyed agreed 20mph speed limits will be ignored by many drivers so are of limited benefit and that limits will not be policed or enforced effectively.”

What do we want? More ineffective and widely ignored measures! When do we want it? Now!