20 mph limit (in East Dulwich)

[SteveT]

I have just had the blurb delivered to see if we want a 20 mph limit.

I voted 'no' for the reasons that it would increase congestion and cause raised outputs of CO2

[silverfox]

No, ridiculous idea dreamt up by some quango with a hidden agenda of social control and oppressing the masses.

Also, be quicker to travel on roller skates

[lpool]

Is this just your road or generally? Would seem strange if generally given most side roads now have signage and raised entrances. I understand Southwark is looking at how the 20mph zones can be policed. Normal speed cameras tend not to work for 20mph zones so likely we will start to see wireless average speed cameras appearing at some point. These have the advantage of catching people who slow down for speed camera and then speed off again. In theory it could clock when you entire a side street, when you re-emerge, the minimum distance you could have driven to that point, time passed, and therefore the minimum speed travelled. If this happens then having an average speed button in your car is quite handy as you can set it when you enter a zone and ensure you don't exit until it gets below 20mph!

[Sue]

Having read the stats about the percentages of children who survive being hit by a car travelling at 20mph (9 out of 10) compared to 40mph (only 1 in 10), I'm voting for the 20mph limit.

I already have it in my road.

I think people drive much too fast down side roads round here, and I'm amazed there are not more accidents.

[Jeremy]

Seems like a great idea for side roads.

Not sure I would want a 20mph limit on Old Kent Road or Walworth road though.

[cate]

I agree with Sue.

[Huguenot]

I'd like to illustrate how 20mph limit will speed up your journey.

Please do concentrate Silverfox.

I'ts not unusual for a 3 mile journey at rush hour in Central London to take 30 minutes.

It's confusing, because at 30mph a 3 mile journey should only take 6 minutes.

This is because total journey time is 'link time' (moving down the road) plus 'junction time' (changing traffic streams).

So in the rush hour journey total 30 mins = 6 mins link + 24 mins junctions.

So at 20mph the 'link time' would be 9 mins as you're going slower.

Hence with a 20mph limit and the same junction time, total journey time is only 9 mins + 24 mins = 33 mins (in practice you won't possibly notice this because of daily variation).

However, with a traffic speed of 20 mph, cars can pull out of junctions more frequently into smaller spaces because the traffic isn't moving so quickly on the destination road.

This means that 'junction time' is drastically reduced. In some cases as much as 50%.

Hence at 20 mph, 'link time is 9 mins, 'junction time' is 12mins - overall journey time is 21 mins - a 30% drop in overall journey time.

Not only that, but it also saves lives.

There really is no more intelligent solution.

I appreciate you don't want to believe that, but that's because people time and again make decisions that are demonstrably against their best interests.

[silverfox]

Ohhhh yeah, that's clever ... 30mph = 30 mins, 20 mph = 20 mins ... I like it, so if we reduce it to 3 mph we'll arrive before we set off

[Jeremy]

Interesting theory Huguenot. I think you've over-estimated the improvement in "link time", as traffic lights and roundabouts would probably require the same amount of waiting.

I don't for a second believe it would speed up the journey, but broadly speaking I don't think it would significantly slow down a typical 3 mile journey around the Dulwich area.

[Huguenot]

No, at 3 mph the link time would be 60mins and the junction time still around 5 to 10 mins, hence total journey time would be around 70 mins. Quite a bit slower. The optimum speed is around 20 mph - that's why it's being recommended.

The irony, Silverfritz, is that you'd love it even more because it reduces the requirement for traffic lights.

Traffic lights tend to be forced upon junctions where the time taken to approach a junction at 30 mph is less than the visible distance of oncoming traffic.

Lower the speeds and fewer junctions need traffic lights - meaning even less time rapping your fingers giving way to non-existent traffic coming the other way.

It's ALL win for you Silverfunk.

[Huguenot]

Fair comment Jeremy, the link time calculation isn't guesswork - however there is no consistent figure as every junction and route works differently.

Traffic scientists measure it in test scenarios, and the key point is that it is significantly shorter than in a 30mph zone.

The final point is about CO2 and pollution.

Altough engines are less efficient at 20 mph rather than 30mph, they spend less time idling at junctions and less time accelerating hard to the desired speed.

This means that in practice there is no significant difference in CO2 output between 30 mph or 20 mph in an urban scenario.

[silverfox]

Oh well, in that case sign me up.

One slight problem though is I drive a Prius so I can't stop at traffic lights or anywhere else for that matter.

[sanity girl]

I am all for a 20mph limit, for the reasons Sue gives above. My daughter was recently hit on a zebra crossing (in her buggy) by a car going at approx 10mph. Luckily she only suffered a graze to her face, but the damage to her buggy from the impact was alarming, and it was literally wrenched out of my hands and flew a few metres across the road. Drivers, please slow down and don't drive like idiots - do you really want a badly injured or dead child on your conscience for the rest of your lives?

[kford]

Isn't most of SE22 a 20mph zone anyway?

[Ladymuck]

Well, as a cyclist - a reduction in the speed limit suits me fine. It might even encourage more people to take to their bikes - thus potentially lowering C02 emissions.

[James Barber]

I'll try and get a copy of the 20mph counsiltation. I have a draft but not the final published version.

We've spent some months discussing with officers the areas covered.

[MitchK]

20mph is a good idea, although most journeys through London are completed at 10mph at best.

How about some traffic calming measures on Lordship Lane - speed bumps or 20mph limit? And a pedestrian crossing outside Somerfield to replace the ludicrously positioned crossing by the Goose Green roundabout.

[James Barber]

Hi Mitchk,

Traffic calming measure like speed humps would be really disruptive to buses and the buses would soon flatten them out. Buses have very high axle weights which really pound bus stops - see Lordship Lane Psot office, Chener Books, Sea Cow, East Dulwich station.

But I'd bee keen on 20mph speed limit along Lordship Lane and we have a completed public consultation and funding in place for a Pelican Crossing outside Somerfield on Lordship Lane.

Goose GReen having zebra crossing seems to work really well. Pedestrians crossing seem to keep the roundabout calmer allowing all arms a fair chance to get round.

Huguenot, fascinated to read about junction and link times.

[MitchK]

Thanks James, I take your point on speed bumps. I think it is vital to keep the flow of traffic moving but Lordship Lane is now a busy shopping street and improving the lot of the pedestrian would be worthwhile.

[kford]

Shared Space is the way forward. Works in the Netherlands and, anecdotally, in the UK too:

http://www.hamilton-baillie.co.uk/index.php?do=projects

[Huguenot]

I like shared space too - I think we'd need lower speed limits first.

[kford]

Shared Space is designed to lower limits, and make drivers/road users/pedestrians more aware of each other. After all, speeding accounts for only around 7% of accidents - most are caused by driver inattention, like talking on the phone or fiddling with a satnav.

When the traffic lights failed at the top of Dog Kennel Hill once, it was impressive to see how everyone - pedestrians and motorists alike - used eye contact between each other to negotiate the junction safely and slowly.

[Sue]

sanity girl Wrote:

-------------------------------------------------------

> My daughter was recently hit on a

> zebra crossing (in her buggy) by a car going at

> approx 10mph. Luckily she only suffered a graze to

> her face, but the damage to her buggy from the

> impact was alarming, and it was literally wrenched

> out of my hands and flew a few metres across the

> road.

xxxxx

How frightening for you both, hope you weren't too traumatised.

[sanity girl]

Thanks Sue. It was pretty shocking at the time but we are both fine now. My daughter talks about it quite cheerily and has even re-enacted events (ambulance, trip to hospital etc) with her teddies!! And she is still fine with buggies and zebra crossings. I am now super-paranoid about crossing the road at all times and am myself driving more slowly since it happened.

[Sue]

Was the car driver prosecuted?