Transport mitigation in EIA
Transport specialists from SLR discuss the importance of assessing the effects and impacts of mitigation measures and introduce the firm's new "trip-banking" approach
Environmental impact assessment (EIA) has been, and will continue to be, an important tool in helping the UK to minimise greenhouse-gas emissions, reduce the social impacts of new and existing developments, and to contribute to a thriving and sustainable national economy.
However, while guidance is plentiful on issues on how to consider the effects of schemes, there is limited guidance and few best practice models that can be drawn upon to advise EIA practitioners on considering the effects and impacts of mitigation measures.
Indeed, if we take, for example, a development whose vehicular trip generation materially worsens congestion on key sections of the highway network, increasing vehicle emissions and noise, the general response among transport professionals is to look for an engineering solution that increases the available network capacity and avoids such effects.
What isn’t typically the case, however, is the application of our transport expertise to the problem in an environmental context. Such an approach would identify alternative forms of mitigation and compare their respective environmental effects to determine the most environmentally-prudent course of action.
Naturally, there will be many occasions where there are no suitable alternatives or where the difference between alternatives is immaterial. However, there will inevitably be instances where this is not the case and, in light of the fact that EIA should provide rigorous, logical and credible assessment of all potentially significant effects, this approach should be considered, at least to some extent.
For instance, while road engineering improvements may mitigate the effects of a scheme, emissions will be generated through construction and the curing of materials.
Furthermore, creating new network capacity often releases latent traffic demand that worsens the environmental effects of traffic.
Alternatively, measures that seek to influence travel behaviour in favour of non-car modes may be as successful at mitigating the effects of development. Such measures can achieve longer-term, and perhaps permanent, emission savings compared to the relatively obvious approach of installing new road capacity, by encouraging a shift away from car travel to more sustainable, and socially equitable, forms of transport.
This approach is not difficult and can be undertaken to varying degrees. At its most basic level, travel planning is three-stage process first identifying the opportunities and constraints associated with travelling to a development by use of non-car modes, and then developing a package of measures that will encourage the uptake of non-car travel.
The final stage is the transmission of this information informing people of their available travel options and the consequences/benefits associated with each; the intention being to encourage a switch away from cars.
Historically this process has been applied in the context of isolated developments to reduce the vehicular trip generation of that particular land use. However, because in most circumstances there will remain a residual need to travel by car, the best that can be achieved is minimising travel by car to a practicable level.
In more recent times, however, the approach has been extended to encompass wide-area travel initiatives that bring together multiple trip-generating land-uses under a single overarching travel plan.
This increases the number of single-occupancy car journeys that can be prevented to such a degree that it can be used to offset the residual trip generation of the development seeking to mitigate its trip-generation effects.
While this process has not been undertaken under EIA, the approach has been used to support the planning application for a development comprising more than 1,000 residential dwellings in Huntingdon, Cambridgeshire. In this case, with carefully crafted travel behaviour surveys across several business parks, it was possible to demonstrate to the satisfaction of the local highway authority and Highways Agency that the development would not result in an increase in vehicular traffic on the adjoining highway network.
Not only has this approach, which we term “trip banking”, unlocked the potential of that development site, but it has also reduced the need to make large-scale improvements to the existing highway network, which would have led to short-term environmental effects associated with emissions from their construction and the curing of materials.
More importantly, however, the approach will ensure a long-term saving in vehicle emissions, as a result of a fewer car journeys when compared with the traditional approach of installing new capacity.
In view of this, trip banking has significant potential to assist in delivering the objectives of EIA and to become a keystone of best practice models, sitting alongside an explicit presumption in favour of deploying the most environmentally-prudent, practical and commercially-feasible mitigation.
This is not to say that all EIA development should adopt a trip-banking approach. Rather that, in the interests of showing a rigorous, iterative and credible approach to EIA, the potential opportunities and constraints associated with all mitigation measures should be set out to ensure informed decisions are made.
This article was written as a contribution to the EIA Quality Mark’s commitment to improving EIA practice.