Thursday, 12 September 2013

Reminder: We are a data driven organisation that understands how things work

Some people -mistakenly consider us to be some kind of spoof, whereas in fact we are a documentary that has built up a weakly-defensible dataset of the city's transport issues.We also include topics like queue theory, game theory and the like to analyse that data.

This is why we despair when the legacy mass media publish articles that lack both real data and the fundamental understanding behind it

Now, Queue theory, Erlang's core concept: A queue happens when the egress rate of a channel is lower than the ingress rate.

In less technical terms "you get a queue if less things are leaving something than entering". It doesn't matter how big a bucket is, if more watering is pouring into it than is leaving from a hole in the bottom -eventually it will overflow

In evening post commenter terms "there's no point making something two lanes wide if it has to go down to one lane wide a bit further on". The bottleneck is the one-lane bit wide, not the two lane stretch.

We know this is hard to grasp, which is why people are still complaining about the Portway bus lane. Evening Post Commenters: the bottlenecks are the narrow bits beyond the suspension bridge and Anchor Road -removing the bus lane will not increase your journey time by car at all.

Alternatively: it is futile to remove a bus lane in the name of congestion, if there's a single-lane road later on. You are wasting your life on something that will not deliver the benefits you expect. You may argue against this using the term "common sense" -but that is why building things from bridges to computer networks rely on people called "engineers" trained in something called "mathematics". Common sense doesn't cut it when you actually want something to work.

The Evening Post reporters need to pick this up too.

As today there is an article, Traffic lights on Blackboy Hill 'are cause of the congestion'.

A BRISTOL campaigner claims a set of traffic lights at a busy junction cause more congestion than they solve – and should be ripped out.
Simon Brookes, who led a campaign for the removal of a controversial bus lane in Westbury Road, is now calling for the removal of the lights at the top of Blackboy Hill.
We aren't sure what "campaigner" means here. Presumably it means "someone who doesn't understand queue theory but likes to get their face in the regional press"

He conducted a survey and claims that the lights held up lots of buses.
Mr Brookes carried out another survey yesterday between 9am and 10am. He said he witnessed 89 changes of the lights and during that time, only two buses went through on green. But the number of buses going uphill and held up on a red was 26.
We are surprised that Mr Brooks has now started caring about buses. Because if you are trying to get bus lanes removed on the approach to Whiteladies Road, suddenly caring about their performance in Whiteladies Road itself seems somewhat hypocritical -unless you are simply pretending to care.

Furthermore, if you are going to do a survey on congestion -why do it outside the rush hour. Do it at 08:30 at peak commute and school runs. Doing it after 9am is like saying the M32 doesn't get congested because you drove up it on a sunday morning.

Bad data, failure to root cause analysis and then pretending to care about public transport. We don't do any of these.

Mind you, Mr Brooks' pretence to care about buses doesn't make it through the article:

He will also be calling for a cycle lane to be removed from Westbury Park, where it meets with North Road.
He said the lane was not used by cyclists and simply added to traffic congestion.
Mr Brookes also wants to see the removal of the remaining stretch of bus lane from Westbury Park.

Sorry, but the congestion has other causes. It may seem frustrating to be stuck in a car watching bike lanes and bus lanes that are empty most of the time, but that is because they are working. The buses are not being held up until they merge with the cars on Whiteladies road; the bicycles not held up at all, mostly.

Here then is our dataset: a video from  "wheels on the bike" counting the entire set of vehicles on Whiteladies Road, from the top to the triangle, in 1:45.

Most of Whiteladies road is one lane wide. That is the bottleneck -the carrying capacity of the road. Arguing about bus lanes  up the hill or even switching times of traffic lights is irrelevant when there is a lane traffic jam from Park Row and Park Street stretching all the way up to the Downs.

This is why appearing on papers demanding for things to be removed because they "cause congestion" is dangerous. Someone may one day see this video and say "maybe there are other issues". We know that -it's the surburbanites driving into town. Simon Brookes should recognise this, and keep his mouth shut.

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