Friday, 27 September 2013

Those bus lane comments - what do they mean?

Liverpool City Council's Cabinet today (27th September) agreed to get rid of all the bus lanes in the City for a "trial" nine months starting at some point in October.

The coverage of the decision in the Echo today has this quote from Mayor Joe Anderson

“We’ve reviewed them  (the bus lanes) over the last six months and we will compare that data with what we gather over the next nine months."

The Echo had a journalist at the meeting so there's no reason to doubt the accuracy of this quote.

But what on earth does it mean?

It appears to say that the existing bus lanes have been monitored carefully and data collected over six months.

So no doubt there is all sorts of statistical information used in the decision (the data).

Now decisions at these sorts of meetings are pretty much based on the material in reports provided for the committee.  And you can read the report for this one on the Council's website at this link.

Now there are several types of data that might be useful for an exercise like this.

You could count the numbers of buses and cars in various lanes and compare these to data from before the bus lane introduction.

You could time a typical car journey and compare it to a car journey from before the bus lane introduction.

You could look at numbers of passengers on buses using bus lanes as opposed to routes without any, and compare these to pre bus lane times.

You could measure air pollution in the areas near bus lanes and compare with data from before the introduction of the lanes (air pollution is one of the problems linked to traffic congestion).

You could measure traffic flows on "rat runs" and draw some conclusions about whether drivers are attempting to avoid roads with bus lanes.

And there are quite a few other data driven things you could do.

Now some of these bring their own problems.  The obvious is how you  control for other variations
 ( growth in car ownership, change in population, changes in bus fares, impact of roadworks and so on).  But they all have the benefit that they produce figures and could be viewed in graphs as trends if collected in a certain way.

So what exactly is the Mayor's data?

Well the report admits there is no up to date figures on bus useage (why?) but then goes on to use material from cameras overlooking the lanes (thus sidestepping the issue of lack of data from bus lanes without cameras).  And we get some pretty vague statements with no numbers attached. We're also told that officers have monitored these lanes directly (implying standing by the road rather than using a camera). But we're not told whether this monitoring consists of sampling and if so how often and at what time of day (there is nothing wrong with sampling but you need to know it's been done)

To be honest this "data" is nothing like data and is more a series of "ooh terrible traffic" type semi anecdotal statements.

Now it's perfectly possible to make decisions based on gut feel or impressions.  But if you do that you shouldn't claim you are using evidence (because you are not).

It's certainly true that some very specific problems have been identified, and these are listed in the report.  But isn't that an argument for looking at those specific problems rather than deciding on a blanket ban?

I am pretty agnostic about bus lanes.  I think if they work (and we need to define what we mean by work as the report certainly doesn't) they should stay and if they are not serving a purpose, or if they are not working, they need to be reviewed.

But I suspect this "all or nothing " approach will simply bring more problems to the very streets it's claimed it'll help.

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