Stressin’ the Travel Demand Analysis Exam


“Oh bloody hell…. *%%#@@*&@& Did I really sign up for this? Sarah, my head hurts.’ ‘Yes Josh that’s because there’s a grim looking maths equation floating in the air next to you.’ ‘What does it mean, Sarah? I’m totally lost.’ ‘Well Josh, to put it in terms you can relate to–it’s not actually carbon, but it may as well be. That equation predicts the change in the number of people using one mode of travel, say cycling or walking, if the cost and convenience of travelling by each mode changes. So if say petrol went up to 5 squids a litre, the cycle path would be quite an ‘appening place to be– even more than it is now.’ ‘Oh right, so you can actually mathematically model how people respond to changes in their travelling environments. Ok….well that should be useful… thanks Sarah!” (Sarah is my good friend and fellow full time transport planning student, and the above photo was taken during last minute revisions about an hour before the Travel Demand Analysis final exam on Monday- don’t know what I’d do without her.) Yes the transport modelling formula above is indeed an ugly specimen, yet it turns out that it is rather important to know. It is, among other things, used in transport planning to predict the traffic generating effects of new road or expansion projects and the traffic inhibiting effects of road space reduction (as for a park, bike lane, or traffic calming scheme). Here in the UK, since the government’s 1994 SACTRA (standing advisory committee on trunk road assessment yeah brits have nasty acronyms too) report, there has been some official acknowledgement that road traffic (i.e. human psychology) tends to behave much more like a gas than a liquid- it expands to fill new space, and contracts if the amount of space is reduced. (though these studies of course continue to be widely ignored…) We learned in our module that empirical evidence from 60 international case studies showed that when the capacity of a road was decreased (a road diet, lets say), the average reduction in traffic on the treated road was 41%. Overall reduction in traffic was 25%. This so-called “variable demand” can provide justification for new projects to re-allocate general road space to create open space, and networks of bikeways, rail and busways. Taking away car capacity from our roadways can actually relieve congestion! We can make the streets safer and our public transport systems more convenient- and drivers won’t have to suffer as much in gridlock! This psychological reaction is not very intuitive, unfortunately, and that may explain why new roads continue to be built and widened and elected leaders throw up their hands in frustration, as below: Well the exam went okay in the end, and I realised that I had probably absorbed more than I realised. I also burnt the midnight compact fluorescents, (oil is so 20th century) finished my four papers, and handed those in last week. Other than that, things are going along well in this land of wheelie bins and mince pies- we’ve been having an unusually mild winter that is making our bulbs come up in January. We have a new roommate from North Carolina named Missy who moved in at the beginning of the month, who rides her Marin hybrid to her job as a speech therapist. That makes us officially a car-free household, and are planning a party to celebrate after Bristol Critical Mass on January 26th: The theme for the evening is: transport and climate change, so come dressed up as Michael O’Leary of Ryan(don’t care about the) Air or Stellios of Sleazyjet or something…. No i am not gearing up for a raid on the north sea oil platforms in the pic below- i was bundling up against extreme weather of 60 mph winds and horizontal hail during a walk along the Pembrokeshire Coast over New Years. Leah and I took a train with our bicycles to Fishguard in Wales, then rode the last 15 miles to the bunkhouse on Pwll Caerog Farm. Reminded me of Point Reyes National Seashore north of SF where I’ve spend the last 3 new years. Nice to get away from Bristol traffic and it certainly blew away the cobwebs, for sure….. “

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