10.3.4 Interdependence of Land-Use and Transport Options

It is sometimes the case that land-use and transport options are worked up in tandem and that, in appraisal, a circular argument seems to arise whereby:

• The viability of the land-use option depends upon the implementation of the transport option; and

• The viability of the transport option depends on the trips that would be generated by the land-use development.

Such a situation is bound to make it difficult to establish the true merits of either option. However, Scottish Government research entitled Key Sites Appraisal Methodology for Development Planning (2001), produced findings that are incorporated in SPP17. One of the key objectives of the guidance is to locate major travel generating uses so that they can support more sustainable travel patterns. The original research document includes a useful glossary of terminologies for "key sites" relevant to the work being undertaken. Other research work results incorporated into SPP17 include An Integrated Approach to the Transport and Land-Use Planning Aspects of Development Applications, which is a helpful background example on transport assessment or travel plans. The following is proposed as a rule of thumb to help disentangle the respective impacts of the options:

• The total costs and benefits of the combined options should be appraised against the established Land-Use objectives (probably set out in the local/structure plan) with the accompanying question: "could the land-use objectives be better achieved by some other means (perhaps involving other transport options)?" Here, the better achievement of land-use objectives should reflect a measure of value for money which will be a matter of judgement for the relevant land-use planners;

• The total costs and benefits of the combined options should also be appraised against the established Transport Planning Objectives with the equivalent question: "could the Transport Planning Objectives be better achieved by some other means?"

Where the answer to both questions is "yes" this would appear to present a mandate to reconsider the wisdom of both options, subject to the following further test. Two answers of "yes" imply that there exist preferable alternatives in each case. The combined costs and benefits of these alternatives should be looked at against those of the original combination. If the costs and benefits of the alternatives appear preferable to those of the original, this would strengthen the case for review. If not, there may be an argument for the original combination on the grounds of "net" savings. This would not be conclusive but the very exercise is likely to have prompted a sufficiently thorough analysis of the options to ensure that the precise relationship between component options is much better understood.

By the same token, if the answer to both is "no" there would seem good cause to proceed with both. In a mixed case, it would make sense to see the combined options as serving the aims for which they appear optimal (e.g. if a better way of meeting land-use objectives cannot be found then the package of land-use and transport options should be seen as serving land-use objectives first and foremost). This should help to clarify the appropriate planning and funding paths.

The totalling of costs and benefits is likely to be only nominally possible - it will probably be a process of juxtaposition rather than aggregation.