Friday, 27 March 2015

Bristol's 20 mph zones: it's the hot cars that lose

The 20 mph zone has been up for a year now, so it's time to review it as drivers
  1. It doesn't make things slower. Really. It's the delays at junctions & in queues that increase journey time.
  2. It makes things calmer. There's less pressure to put your foot down when you do clear a junction.
  3. Similarly, as you approach a junction, you can coast down more gently. 
  4. As you are going a bit slower, you can take time to look around, which gives you a better view of pedestrians. This is tangibly better at night.
  5. It actually helps you pulling out from side roads to main roads. Why? As everyone is moving slower, the time window for you to do things like pull a right turn with cars approaching from both directions is larger.
  6. Fuel economy? No obvious difference. The engine may be less efficient in 3rd than 4th, but you don't have to accelerate so hard, and can coast down. Of course, anyone in a hybrid car is laughing as their petrol engine can work even less, and gain more regenerative braking from the gentle slow down.
  7. Keeping track of your speed? Third gear low RPM seems to work. If you feel the need to go to 4th, you are going too fast. 
  8. Does everyone follow 20 mph? 22-25 is more realistic daytime speed; at night the speed goes up to 30 until the minicabs come out, when it ramps up 40 mph just when the drunk people start walking home.
  9. Increased road rage? No obvious difference. As the average commute speed is < 20 mph in Bristol (TomTom's unverified data, not ours), it's hard to see how it could be made worse.
  10. Collapse of businesses due to increased white van journey time. Not obvious. Congestion is the limiting factor, not maximum speed.
  11. Passing Bicycles? No harder or easier. It's still irritating to be behind someone going along at 12 mph. But the speed limit doesn't make passing harder. We just want fitter cyclists out there.
  12. Then there's the "two shopping trolley" man wandering round the streets these days. We have no idea why he has two shopping trollies full of his entire belongings, but he does, he goes down the roads (not the pavements) at about 4 mph. Again, 20 mph doesn't make a difference.
So who loses? People who spent money on fast cars. You shell out all that cash for a nimble toy, for an extra digit or two at the end of your car brand logo —"i", "GT", etc—, tinted windows and some wheels that just scrape easily.  The key "performance" benefits are tighter suspension, and most of all the ability to accelerate better. 

Which is now utterly wasted, as most vehicle's 0-20 numbers are relatively similar. And pootling around at 20 mph means no need for suspension that lets you do 90 degree turns at 35 mph.

That's enough to drive you to road rage: not the fact that you are doing 20 mph, but the fact you spent a lot of money on your status toy and are doing 20 mph.  Even if you want to go faster, there'll be someone in front who doesn't, who appears to drive at exactly 20 mph on a fast ratrun road  like Ashley Down, Pembroke Road or Filton Ave. It's almost as if some people, on noticing an important person driving a high-end Audi or BMW SUV actually take their foot off the accelerator, dropping from 24 mph to 20. Which we consider unacceptable and strongly condemn anyone doing this.

For those people who have spent the money, they expect something in return.

Fortunately, every so often the opportunity arises. Here is one our instrumented tax-dodgers going down Nugent Hill, Cotham, using the bike contraflow to get to the Arley Hill evening traffic jam, and so on to Stokes Croft. As they join the Arley Hill queue, you can see a green light allowing some traffic to slowly get out to places more interesting.

And here you can see the BMW 3 series YF57KTE getting some return on investment. First they can come off the speed bump while accelerating (suspension), then put their foot down to catch up with the cars in front. Those cars in front who are going through on orange we note.  But as the BMW is now almost joined up with them, it can do the "part of the same group" gambit and carry on through on the red light.

That tactic has given them a bit more speed than the vehicles in front, forcing them to negotiate what is effectively a chicaned right turn fairly aggressively: that suspension at work again.

They then need to put their brakes on, not because of the speed limit but because they've caught up with the car in front.

There: 15 seconds of real driving, out of probably 30 minutes of suffering. Not much —but that's all a 20 mph zone offers, at least during the early evening commute.


amoeba said...

The Mini that pulled-out @0.15 looked like it might be a bit close, but it's hard to judge distances with certainty because this is affected strongly by the angle of view of the camera, there seemed very little barrel-distortion, so I assume the angle of view isn't anything like the 170 degree fish-eye lenses normally used on such cameras.

I didn't notice it in the video, but all too often traffic queues are held-up by people gazing gormlessly at their phones while sat in the queue and failing to pay attention and not noticing the light-change. If only there were some means of detecting / deterring phone use by drivers, the queues would move faster.
As for boys' toys, I hate them.

Bristol Traffic said...

-Problem with the Mini is there isn't great visibility from those side roads; on the DH you need to plan for that and not go up to speed. It's worse on the bottom one because only bikes go straight on, cars pull out assuming its clear. This is why the speedo on the video says ~20 mph max. I don't recall the car being that close, though I wasn't over-happy.

Queues & Texting? Arley Hill is a classic previously documented. Saw someone there with a tablet last month -though without a helmet cam I couldn't show. On the same ride as the video shown here there was a school-run-mum texting, but the helmet camera wasn't positioned right for that video.