Petrol, Postage and Pasties: (1) Petrol
Three stories in the UK news where an OR modelling approach could contribute to the debate. Let's start with petrol (or rather, vehicle fuel). There is a threat of a strike by the majority of fuel tanker drivers (news story here) which would mean that filling stations could run short of fuel. The threat has been reduced because the union and employers have gone to arbitration.
However, public announcements about the talk of the strike have provoked a panic reaction by drivers. There are queues for fuel, and some filling stations have run out of fuel. And once these panics have started, then more people think that there is a need to stock up on fuel, so the queues get worse. Behaviour changes, as drivers choose to purchase more fuel, or to fill up more frequently.
Letters in the press, and callers on the phone-ins on radio, suggest an assortment of solutions. The usual is to ration drivers ("no more than X litres" or "no more than £Y in value"). This has little effect on behaviour, because the ration is usually set higher than the median amount that drivers purchase at a time under normal circumstances. It is not a deterrent, because one of the principal changes in behaviour is to buy fuel when the tank is half-full, rather than quarter-full. The inventory of fuel carried by a typical vehicle normally varies between quarter-full and three-quarters-full, and when there is a panic, it tends to be fuller, and the range is smaller. Another popular solution is reverse rationing, that customers must buy at least some minimum amount of fuel. There are advantages to this idea, as the consequence is thought to be fewer customers of the kind who change their behaviour to "fill up every time I see a source of fuel". However, not all vehicles are created equal. So a minimum of 20 litres may be OK for many larger cars, but cannot be suitable for a motor-cycle or small car. And policing the scheme is very difficult. How does the cashier deal with someone who has bought less than that minimum?
Operational Research models of the situation are limited in their validity, because they are dealing with the unpredictability and irrationality of human behaviour. Most OR models are rational!
However, public announcements about the talk of the strike have provoked a panic reaction by drivers. There are queues for fuel, and some filling stations have run out of fuel. And once these panics have started, then more people think that there is a need to stock up on fuel, so the queues get worse. Behaviour changes, as drivers choose to purchase more fuel, or to fill up more frequently.
Letters in the press, and callers on the phone-ins on radio, suggest an assortment of solutions. The usual is to ration drivers ("no more than X litres" or "no more than £Y in value"). This has little effect on behaviour, because the ration is usually set higher than the median amount that drivers purchase at a time under normal circumstances. It is not a deterrent, because one of the principal changes in behaviour is to buy fuel when the tank is half-full, rather than quarter-full. The inventory of fuel carried by a typical vehicle normally varies between quarter-full and three-quarters-full, and when there is a panic, it tends to be fuller, and the range is smaller. Another popular solution is reverse rationing, that customers must buy at least some minimum amount of fuel. There are advantages to this idea, as the consequence is thought to be fewer customers of the kind who change their behaviour to "fill up every time I see a source of fuel". However, not all vehicles are created equal. So a minimum of 20 litres may be OK for many larger cars, but cannot be suitable for a motor-cycle or small car. And policing the scheme is very difficult. How does the cashier deal with someone who has bought less than that minimum?
Operational Research models of the situation are limited in their validity, because they are dealing with the unpredictability and irrationality of human behaviour. Most OR models are rational!
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