During a bushfire, the bottleneck is rarely the number of shelters - it's road capacity. This study builds an optimisation model that reverses selected road lanes (contraflow) to double their capacity, while explicitly scheduling the elderly and people with disabilities. Tested on Australia's 2013–14 Gippsland bushfires, it clears far more people, far faster. Explore the network below.
Bushfire spread (orange) with direction arrows, the ten affected communities (red), three shelters (green triangles) and the road network.
A schematic of the same network. Communities (red) evacuate through transit nodes to shelters (green). Scrub through the 3-hour window, or toggle contraflow to see routes double in capacity and the queue drain.
A variation test shows edge (road) capacity dominates - far more than route capacity or the time window.
With contraflow the full population is cleared; without it, evacuations fall to ~1,787 and split unevenly across shelters (Churchill 45% · Traralgon 36% · Rosedale 18%).
Where the network can flex with contraflow, 84% of the population reaches shelters and total clearance time improves by up to 60% - directly reducing exposure and potential fatalities.
The model is a large mixed-integer non-linear program. A custom decomposition solves real-world sizes where a commercial solver stalls.
CPLEX fails on the large instances entirely; the accelerated Branch & Price returns optimal solutions where it cannot.
14.26% faster than base B&P at the same optimum, and 3.53% better solutions with 12.03% less compute than Reihaneh & Ghoniem (2019).
Invest in the edges that carry the most evacuees. Capacity on key roads reduces congestion and clearance time more than adding shelters or transit nodes.
Identify which two-way roads to reverse, and when. Contraflow is the single most effective lever for draining the queue during a surge.
The elderly and people with disabilities need vehicles, time and routing planned explicitly - the model assigns them first to avoid being stranded.
Extra shelters don't raise totals much, but the right placement balances the load and shortens the longest trips.
A research showcase on reversing road lanes to speed regional bushfire evacuation.
Network flow models pick which links to reverse to maximise evacuee throughput in time.
Contraflow helps most on a few critical arterials - see the maps.
