Mill Road bridge closure the ideal opportunity to collect data that informs the future of the street

This article was published in 2019, in Magazine 142.

Image as described adjacent

The railway bridge ‘closure’ provides Mill Road with a once-in-a-generation opportunity to ‘trial a change’. The temporary change must be big enough to tell us something, but not so big as to be unrealistic to continue with in some form, and we must collect the right data to enable a debate about what to do next, rather than a debate about the data.

If we identify and roughly rank Mill Road’s transport problems, through-traffic (that adds nothing to local business and isn’t created by residents) would seem to be the highest priority to address. The bridge closure gives us that opportunity, but it must be supported by a properly designed study that starts by deciding what questions it wants to answer (e.g. where is motor traffic displaced to, how much traffic evaporation takes place, how does foot and bike use change, what happens to air quality and trade figures), and then collects data to answer those questions.

With motor vehicles unable to cross the bridge, there will be some change to car-borne resident behaviour – we need to know how much and design that in. We could go further and, by using plate recognition, build up data that tells us how many residents, delivery vehicles and incoming visitors are moving about at different times. That could then be used to answer questions about the effect of evening ‘street scene’ speed limit changes or temporary re-routing, delivery time restrictions or bigger delivery windows.

Of course the severing of a bus route is problematic; it is a change that is too extreme to suggest that it should remain after reopening. The answer is to run something as close to a replacement as possible (perhaps minibuses from Perne Road to the foot of the bridge and from the Petersfield foot to the other end, with an electric shuttle cart crossing the temporary bridge). I would hazard that even that complexity is no slower than the bus during most of the daytime.

After the closure, the data need to be publicly available (but anonymous of course) and the analysis and presentation should be open and peer-reviewed.

In summary then, we need to design the data collection with our questions in mind, we need to put in temporary solutions to the things that wouldn’t form part of any proportionate plan in the future, and we need an open process where we can play around with the data and ask ‘what if’.

Finally, ‘evidence’. I realise that the traders association is concerned about a drop in revenue. My profession is not this kind of thing (although it is in evidence for decision-making that has similar challenges), but I lived in Whittlesey 25 years ago when something similar on a smaller scale was proposed for the high street, and it was the case then that all the properly-conducted and peer-reviewed studies showed that when motor traffic was reduced and other transport forms increased, revenue went up. That, to me, seems an easy win – get a research group to review and feed back on the available evidence. Then design the Mill Road bridge closure experiment in the same way.

I’m not an advocate of any outcome, but I do know that the peer-reviewed evidence on the effects of air quality and noise on human health is compelling enough to warrant significant investment in getting the data we all need to make an informed community decision. Let’s decide what questions we want to answer (not what solutions we envisage), collect data to answer the questions (be they ones about traffic, air quality, trade figures or perceptions) and then let’s see what it can tell us. This way, we can avoid any of us promoting a solution without fully understanding its impacts.

This article by Steve Gibson has been slightly abridged. The original piece was first published on 18 November as a comment on the Mill Road Bridges website ( and is republished here with the kind permission of the author.

Data update: finding out more about Mill Road

Our campaigning about data seems to be paying off as, at the start of the year, the county council issued a request for quotations for traffic counts with a view to gathering data about through-traffic before and during the bridge closure. It specifies that the traffic sensors used must be capable of collecting pedestrian and cycle data and will carry out counts 24 hours a day along key transport corridors. A separate investigation into changes in air quality is also underway.

Meanwhile Camcycle continues to work with volunteers and students from Cambridge Hub on our own data-gathering projects including interviews with traders and customers along Mill Road.