Queues at Heathrow: a numbers game

5th May, 2012

‘Heathrow passport control misses target’

Financial Times, May 3

How bad are the queues, actually?

Damian Green, the immigration minister, has told parliament that the worst queueing experience was an hour and a half, at Heathrow last week.

Sorry – the worst queue at Heathrow last week was an hour and a half, or Heathrow was the place with the worst queue, ever?

Good question. Meanwhile, Heathrow’s operator, BAA, released data showing the worst queue was three hours.

I’m confused.

The way in which the statistics are gathered and reported doesn’t help either. The Border Force is supposed to ensure that passengers from outside the EU get through immigration checks within 45 minutes 19 times out of 20, while EU-based passengers should get through within 25 minutes, again 19 times out of 20.

They aren’t exactly stretch targets, are they?

No. The Home Office has been proudly pointing to its latest report that shows all these targets have been hit with room to spare.


Which tells us that things were going smoothly in October to December last year.

Hurroo . . . 

Quite so. And normally we’d just have to wait for the Home Office to get around to publishing data for January to March and finally, in the summer some time, we’d get to hear about what happened in April.

So how come everyone is reporting that the targets were missed in April?

This is unofficial data released by BAA.

Are we comparing apples and oranges, then?

Not really. Both BAA and the Home Office use the same basic methodology. At regular intervals they pick somebody joining the back of the queue and then time how long it takes for that person to clear immigration. There is one difference: BAA picks a person to track every 15 minutes; the Home Office only does it once an hour.

So that might explain why Mr Green and BAA were reporting different numbers.

Yes. Also, the worst cases reported by BAA actually happened shortly after Mr Green had made his statement. Mr Green, incidentally, was trying to have his cake and eat it by using unpublished data to bolster his argument in the House of Commons. His numbers are supposed to be either official statistics or he is supposed to keep them to himself. I suspect the UK’s statistics watchdog will take a dim view of that.

Can we start talking about how to fix the problem now?

Patience. There is one nerdy point about the numbers worth attention. Imagine Heathrow has 10 hours in which 1,000 passengers an hour arrive and walk right through, followed by one hellish hour in which 10,000 passengers arrive and end up camping out half the night.

It’s easy enough to imagine – go on.

Well, in that case half the passengers have had a terrible time. But the way passengers are sampled by both BAA and the Home Office, it was only in one hour out of 11 that things went badly and so only one passenger out of 11 suffered excessive queues. The sampling method they’re using systematically under-samples times when the airport is very busy, which is the very time that queues are longest – Mr Green did, after all, blame “bunching of arrivals” for recent problems.

I get the point. So things may be worse than the official numbers suggest.

Yes. And since the official numbers suggest that almost a quarter of non-EU arrivals at Terminal 5 in April had to wait more than 45 minutes, the baseline is hardly great.

How do we solve the problem?

More staff. As a rough reckoner, if a queue is an hour long and you open up a new desk, every person you pull out of that queue saves an hour of queueing time. If an immigration official can check 60 people an hour then she is saving 60 hours of passenger time for one hour of her time.

But who is going to pay them? The government? The airlines?

The point is, the benefits are greater than the costs, so if the government can’t figure out how to make the queues go away they’re not fit for office.

At least the Border Agency is recruiting, right?

No, they’re going to cut staff by 18 per cent over the next three years.

This is insane! I’m going to complain to the Home Office.

Really? Join the queue.

Also published at ft.com.

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