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Transportation in the 21st century: The modeling/reality gap

Transportation in the 21st century: The modeling/reality gap

by Nina Arron

Traffic modellers seem to be an optimistic breed. The value and construction of many large scale road, bridge and tunnel projects seem to be based on traffic modeling projections that are proving to be overly, or down right wildly, optimistic. There seems to be an idee fixe that traffic will increase, always and forever and ever. Reality however is showing a different trend, a drop in traffic volumes.

A few examples are outlined below with links to articles for those who would like to read further...

A US example
In Bethesda Maryland, near Washington DC, an 18.8 mile toll highway was begun in 2007. The first segment was opened in 2011 and is falling a long way short of the traffic projections with a correspondingly low toll income. To add to the pain of lower than expected income, costs ballooned from $1billion to $2.4 billion, or $4 billion if interest payments are included. Proponents of the development also predicted that the road would lead to economic development in the area but this has not yet occurred. Considering that a commuter making daily round trip use of the road during rush hour can expect to pay $2,000 a year it is not surprising that many drivers are choosing to avoid it.

A Canadian example
The blog Price Tags outlines a number of traffic predictions in British Columbia that have proven to be widely optimistic. The Port Mann Bridge graph is particularly revealing with the actual traffic volume showing a decrease from 2001 to 2011 while every prediction made (2006, 2007, 2011) consistently and optimistically say the volumes will increase. Surely at some point the traffic modellers will have to admit they were wrong and adjust downward….won’t they…?

An Australian example
In Brisbane the multinational AECOM was hired to provide traffic modeling for the Clem7 tunnel. AECOM predicted traffic volume (aka toll revenue) to be a great deal higher than real use. As a result the project is bankrupt and investors are now suing AECOM for misleading them. And just as there are multiple examples of optimistic predictions leading to costly underperforming roading projects in Canada and the US, this is not the only Australian example of traffic projections being overstated. The Australian (article below) also mentions Sydney’s Lane Cove tunnel. This is now owned by Transurban which paid $600 million for the asset, $1 billion LESS than its construction costs and now receives all of the toll revenue.

A New Zealand example?
If New Zealand’s Roads of National Significance share the same overly optimistic traffic modeling and the government decides to sell the assets rather than continue to lose money on debt servicing, then companies like Transurban can buy up these assets for less than their construction cost, set toll rates and own the toll revenue for ever.

For more examples follow this link
Clark Williams-Derry has compiled quite a list of traffic modeling optimism.


Nina Arron Bio

Nina Arron is an urban planner with a passion for Pedestrian Oriented Development. A past resident of Wellington, Nina is currently living in New Rochelle, New York where she has just begun a new project Walk Your Community encouraging people to define their community and then walk it. She has defined her community geographically and is currently walking the 175 miles of streets of New Rochelle. You can read about the project and her progress on her website and blog Better yet, set your own community parameters, start walking, and share your stories with Nina on

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