Voices of Science

What you do is you observe the existing traffic, and you have a different network after the road is built, so you had to reassign the traffic, and reassigning the traffic by cost, perceived cost, partly time and partly cost. And now you’ve got a model which you could either put into the past or into the future. So if I go into the future, instead of having origin and destinations, I’ve got generations and attractions. Like Telford New Town wasn’t there before, it’s there now and it’s generating its own traffic. Where is the traffic going to and coming from? You have to get how much space is devoted to shopping, schools, so on, and each one of the generated by demand. And now you had to assign that to the network and, hopefully, the fact that you’ve got it right in the present means that you’re going to get it right in the future. But of course if the planners make a different set of judgements than the ones you’ve work on, you’re going to get it wrong. You don’t finish the survey now, you do the survey for now and then you make a projection and later on you do the survey again to see [laughs] whether you were right or wrong. And of course you’ll be a bit wrong, and a bit right. ‘Cause you see the new road it makes changes. You put a new road in, and oh, 'I can – I used to go to Birmingham along the M50, but I now go to Birmingham along this M1' or whatever it may be, M40 rather. So people’s habits change because you’ve changed the network. So this is why you need a model to be able to describe how the changes are being made. So there’s a – a predicted population for Telford, and that’s going to generate so many trips to school, non-home based trips, so many shopping trips, and so on. And so you’ve got all these categories and you shove people into them, and then find the extent to which they are being distributed around the country. Absolutely crude in Cardiff, only simple little changes you make, whereas when you get to a whole region, like the Midlands, you’ve got a rather different problem on your hands.