THE DEMON DIAGRAM – THE DEVIL IS IN THE DETAIL

By Andrew Herington

The East West Link is all about traffic, a topic that got a good belting on Day 12.

At the heart of this argument is the ‘demon diagram’ produced by the LMA (so called because it is red and blue – the colours of Mr Morris’s favourite football team). It purports to show the roads that will see a traffic increase (in red) and those where traffic is reduced (in blue).

One problem is the base against which the comparison being made. It is not whether there is an increase or reduction from the traffic levels today but to the levels that may exist in 2031, if the East West freeway is built, and the levels in 2031 if it is not. The LMA say it would be unfair to compare to the current situation as the issue is whether to build or not to build.

When the LMA say a “decrease in traffic” – they actually mean that traffic will increase compared to today. It is just that it won’t increase as much as they forecast if the freeway is built: a funny kind of decrease of you stand at your front door and watch the cars and trucks go by.

Secondly, there are various versions of the demon diagram floating around that add to the confusion. Some show the percentage decline in traffic – putting unusual emphasis on many small streets which have modest traffic and hence it only takes a few cars diverted for it to show a large percentage drop.

Other versions show the changes in absolute traffic volumes  which suggests big increases on the freeways and small drops on inner urban arterials. For example there is a very large increase shown for the Eastern Freeway growing in size until it gets to the Chandler Highway which inexplicably turns into a substantial drop.

A third problem is the LMA modelling fails to take into account any improvements in public transport over the next 15 years – despite the PTV Network Development Plan foreshadowing major investment in new lines. Even the $49 million committed to upgrading the DART Bus service was not factored into the assumed rate of traffic growth.

More fundamentally there is no testing of how the relative mode share would be affected if the amount proposed to be invested in the East West Link was instead invested in public transport.

If they assumed the amount proposed to be spent on the East West Link were invested in alternative public transport projects the forecasts used to produce the demon diagram would be quite different.

Basic data missing from the demon diagrams include the scale and the underlying data to make sense of the diagram and its magical claims

Today, at the request of the Assessment Committee, the LMA tabled new versions of the demon diagram showing the impacts across a wider area of Melbourne. This showed traffic on the Eastern Freeway and Citylink North would increase more than if they aren’t built and the increase on other major arterials only slightly less than currently forecast.  There is no magical solution to congestion on the Westgate and Monash freeways.

There is simply more traffic generated – much of it car traffic to Melbourne Airport. The robustness of these estimates has not been tested against the actual tolls to be charged (or future car parking charges at the Airport, or the delivery of a Melbourne Airport link which both parties say should be before 2031.

All we know so far is that if tolls are 50% more than assumed in the models (say $9 rather than $6 a trip) then traffic on the tollway would be cut by 40%.

The LMA also tried to use 2011 Census data to say that Melburnians have not lost their love of cars. Tabling data for Melbourne, Yarra and Moonee Ponds, the LMA argued that the number of households with one or more cars per household had increased due to rising education levels – suggesting that inner city trendies are hypocrites for opposing freeways.

What they didn’t say is that this increase is far less than the increase in the actual number of households as the inner city population increases. The proportion of households with no motor vehicle is 40.1% in the City of Melbourne – 4 times the metropolitan average whilst in Yarra it is 21.3% – twice the metropolitan average.

Across Melbourne car ownership is increasing – yet car usage is static or declining.  The biggest contradiction in the LMA traffic story remains the enigmatic (and perhaps inexplicable) projection that if the East West Link is built there will be 14.012 million trips per day but if we invest $8 billion in road works there will be 14.018 million trip taken (an increase of 0.04%) –see pages 10 and 11, Technical Appendix E.

The Coalition of community groups opposing the East West Link is offering a prize* for any credible explanation of why an extra 6,000 trips a day is worth $8 billion.

* Sadly only the collected tabled documents from the Hearings

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One Comment on “THE DEMON DIAGRAM – THE DEVIL IS IN THE DETAIL”

  1. David Hanna March 20, 2014 at 8:48 am #

    A wonderful summary – it almost makes me wish I was there. Almost!

    The only explanation I have been able to come up with for the sudden drop in traffic at the Chandler Highway is a new high speed rail link to the city from there so everyone drives there and then leaves their car to avoid the no doubt prohibitive parking fees in the CBD in 2031.

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