mjr wrote:Stevek76 wrote:In terms of impact analysis, on a specific level that's very hard to do for these schemes, most traffic models don't operate at such a fine level of detail and basically none are properly equipped to really understand mode shift to and from walk/cycle.
Oh I think that's being far too kind! The current popular traffic models like TRIPS, ARCADY and so on deliberately ignore walking and cycling routes except for how giving them any extra traffic signal time will increase delays to motorists.
That is not entirely correct but I think you're getting a little hung up on traffic engineering models while I was talking about strategic forecasting ones. Tfl's present strategic model has a cycling network model & after the update a few years ago much of the demand workings operate at a much finer disaggregation of person types, one of the reasons for that change was to better handle the differing propensity to cycle in various conditions by different demographics. Some other models around the country have also made some efforts but none really worth speaking of. A few are built where the demand model covers walk & cycle as modes but mostly just there to get 'about the right mode share' coming out of the demand model and little proper detail representation of the travel costs of either.
However the key issue with LTNs is simply the zone sizes in the models and many of the trips they affect start and end in the same zone. There's a few possible ways around it but all tend to amount to a bit of creative 'professional judgement'.
mjr wrote:so some councils will only do it if someone else is paying (such as the national Active Travel Fund has during the last year) and some are still very reluctant even then.
'Many thousands' is cheap compared to most council transport expenditure, and they will likely save that on maintenance relatively quickly as the wear & tear on roads inside the LTN will be massively reduced whilst the wear on the main roads will be a slight increase in the worst case. Really this is just about political will. If the leadership is willing to tackle car dependency these are cheap and effective measures, and if they're really willing there are several revenue raising tools they have in the form of residents parking permits, workplace parking levies and congestion charges that could help fund such things. Unfortunately, far too many fear the 'motorist vote'. It's electioneering mode in Bristol at the moment and Labour are claiming freezing RPZ fees as something they've delivered!
mjr wrote:This makes no sense when you can get loads of cyclists or even more walkers in the 3.5m x 16m road space allocated to a car travelling at 20mph
? It's entirely the point of such values. PCU isn't a representation of people moved, it's a representation of road space used. The problem is too much focus on maximising PCU moved but this isn't really an issue with the tools as such more a combination of the people using them and (mostly) the answers other people are demanding from them. Tools are produced to answer the questions being asked, that the tools used in the UK are too motor traffic/highway focused is a function of decades of government funding focused at road building. Even then some do have greater capability, for example the signal junction software Linsig has been able to model and report pedestrian delays for over a decade. I'm not aware of any council* asking for this, either for their own work, or of developers.
*except London again, which even insists upon full agent based simulations in busy areas.