Clay Farm: a sticky mess with few cyclists

This article was published in 2007, in Newsletter 73.

The revised planning application for Clay Farm developments near Trumpington and Addenbrooke’s Hospital has been submitted, and I’m attempting to review just the hundreds of pages of its Transport Assessment on less than one page. The Campaign has no official position on the principle of these fringe developments, but I’m sure I’d be even more critical of the Transport Assessment for another Bar Hill or Car Bourne.

I’d rather hoped we’d seen the end of ‘Predict and Provide’, and that modellers using SATURN, the computer program used for planning road use, understood the concept of ‘Garbage In, Garbage Out’, but both these phrases come to my mind when reading this report.

I’ve some serious concerns:

  • Firstly we have the underlying assumption that no pedestrian will walk more than 2 km and no cyclist will cycle more than 5 km. Although such errors may not distort results for other cities with lower levels of walking and cycling, I’m sure it will have a measurable effect in Cambridge. When I first saw a draft traffic model for north-west Cambridge some time ago I thought we had a ‘units’ problem and they meant ‘miles’, but no, it is kilometres.
  • Then we are told that the trip generation (not modal split) is derived from Bar Hill. This work is done by Atkins and although some ‘fudge factors’ are applied, we still finish up with under 14% of trips by bike and over 53% by car. The Clay Farm area is supposed to be having some 40% ‘affordable’ housing. How does that compare with Bar Hill, and won’t such differences cause changes in trip generation and modal split?

I don’t think we should provide for that number of extra vehicle trips, especially with some form of demand management just around the next corner and fuel prices at one pound per litre and rising!

Of course, designing for such flows of motor vehicle tends to be a self-fulfilling prophecy, as junctions with two traffic lanes are needed, hence deterring all but the most confident of cyclists or reducing us to pedestrians at junctions.

Reading deeper, I become even more disillusioned as it appears only 1500 cyclists will make trips that leave the proposed Clay Farm and Addenbrooke’s developments, the other 3000 being ‘internal’. I would hope that none of the 15 000 motor vehicle trips are ‘internal’ to the developments!

I’ve long, long been concerned that not sufficient data has been collected to enable even the pattern of existing cycle trips to be determined. The recent set of surveys only questioned motorists and ignored cyclists: why? Please let us have some enlightened traffic planning in this area that encourages cycling and discourages car trips, and don’t confuse simulations with reality, until you’ve got the parameters right.

Jim Chisholm