Environmental Engineering Reference
In-Depth Information
impacts remain small, due in part to only considering the part of the trip within the urban
area boundary - many deliveries, for example, to London residents or businesses originate
beyond London.
Synergies between policy packages
An important dimension here is how policy packages should be best grouped together to form
a mutually supporting, synergetic strategy. Urban planning, for example, might be used well
to support a higher public transport, walking and cycle mode share. Some policy packages
may not work well together. The potential relationships evident include:
•
Positive and negative interactions and synergies between policy packages/enabling
mechanisms;
•
Double counting of policy benefits (sub-additivity);
•
Positive (super-additivity) and negative multiplier effects - greater or less than the sum
of the parts;
•
Positive or negative snowball effects over time, and the trigger points where these effects
can be identified.
Synergies and additionality effects are poorly understood in the literature. There is little
available evidence on these issues and an additive principle is adopted in the current TC-SIM
modelling. This means that the relationships between packages are not modelled. Some of
the research behind the VIBAT studies has attempted to assess likely effects (Hickman et al.,
2009b) and there is potential for further development of these ideas. Conceptually, it is not
difficult to identify where the most promising positive benefits of policy packaging may take
place, but the real difficulty is in obtaining empirical evidence that can be used in modelling
approaches where synergies are included.
There are at least three difficult (and critical) policy areas that are currently far from being
resolved. The first is international air travel, which has until recently been growing at a rate
of 6 per cent per annum (doubling every 12 years). There is little acceptance of the need for
reducing the growth in demand for aviation, yet emissions from air travel are soon to become
a major problem to the achievement of CO2 reduction targets (Bows and Anderson, 2007).
Even more concerning is the 'troublesome' leisure travel, as it is the high-income cohorts,
who, despite living in (high-quality) urban areas and being environmentally aware, still travel
most for leisure purposes, including by air (Brand and Preston, 2010; Holden and Linnerud,
2011).
Two further problems are evident. One relates to how international aviation should be
accounted for in emission reduction targets. At present they are either excluded (as in most
transport planning analysis concerning this topic) or they are considered as contributing a
major part of city-based emissions. In London, the calculations used in this analysis are that
half the full international aviation CO2 emissions are allocated to residents (Climate Change
Action Plan: GLA, 2007). This is a high proportion as not all air trips end in London, as many
travellers interline between flights (the London hub) and others travel on to destinations in
the UK that are outside London. At present there are very few technological opportunities
