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Worst Case Scenario: Evacuation of the Blue Mountains

The NSW Government has declared a State of Emergency with regard to the bushfires in the Blue Mountains and the forecast deteriorating weather conditions. One of the reasons given for the declaration is the additional evacuation powers this grants the Rural Fire Service (once the actual wording of the declaration is published I’ll be making a post on what exactly are the additional powers it grants). Large areas of the Blue Mountains could come under threat. Though the likelihood of a complete evacuation of the Blue Mountains has been played down the RFS says that it is looking at the planning.

So let’s look at the feasibility of a large scale evacuation. I’ll use a back-of-the-envelope version of the evacuation timeline method developed by the NSW SES.

NSW does have a plan for a large scale evacuation – in the event of an extreme flood in the Hawkesbury-Nepean River (incidentally this plan also calls for the declaration of a State of Emergency – primarily to convey the seriousness of the situation). If there was to be a whole-scale evacuation of the Blue Mountains I would expect some elements of the evacuation planning around a Hawkesbury-Nepean flood to be utilised.

But is an evacuation even possible. Everyone would need to exit via the Great Western Highway, presumably to Sydney

Though the Great Western Highway is mostly double lane, dual carriageway it narrows to a single lane each way in a number of places, notably at Hazelbrook and Woodford. Single traffic lanes can carry 1200-1500 vehicles per hour. Standard practice is to halve this figure to account for emergency conditions, smoke, emergency vehicles, accidents etc. Census figures estimate a total of about 50,000 vehicles owned by households in the Blue Mountains area – experience shows that households will use all available vehicles to evacuate.

The math is pretty simple:

50,000 vehicles / 600 vehicles per hour = 83 hours or about 3.5 days. If Wednesday were indeed going to be catastrophic the evacuation would need to start now.

Even with perfect traffic conditions, contra-flow arrangements (which I highly doubt would be used as they would prevent emergency vehicles from coming in) and only 1 car per household it would still take a long time:

33,000 vehicles / 2400 vehicles per hour = 14 hours

What about trains?

Seated capacity of 6 car V set trains (those normally run on the Blue Mountains Line) is 608. At the peak they run at four trains per hour. Assuming double capacity and an increase to 6 trains per hour you have the ability to move about 7300 people per hour. The census gives a population of 75,000 for the blue mountains. So by train:

75,000 people / 7300 people per hour by train = 10 hours

Now if you could convince a whole lot of households to leave their cars at home, travel with only what they could carry (both of these are pretty unlikely assumptions) and take the train it might be possible to evacuate all the Blue Mountains in about 6 or 7 hours. Still too long?

If it did come to it, an evacuation of the Blue Mountains would be a multi-day round-the-clock operation involving massive coordination of transport assets, traffic control and a huge effort to convince the community of the need to leave very early. It would need to be called long before the fire was directly threatening properties – in the worst case the decision would need to be happening now.


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