Environmental Engineering Reference
In-Depth Information
transport CO2 emissions and to transition towards a low carbon mobility future. Moving from
carbon inefficient travel to carbon efficient travel means a composite strategy of realising
fewer trips, reduced trip lengths, mode shift and increased vehicle efficiency. Relying on one
set of these mechanisms (e.g. increased vehicle efficiency) is likely to be offset by 'adverse'
trends elsewhere (e.g. more trips and increased trip lengths). Hence any aggregate gains will
be small, if any at all. Again, this seems to be a difficult point to appreciate in national govern-
mental circles, certainly at the political level.
Over 150 individual policy interventions were reviewed in the VIBAT-London study that
may help reduce transport CO2 emissions. Individual measures work best within packages,
allowing complementary measures to work together and mitigation impacts to be quantified.
Hence measures are grouped into complementary policy packages as components within
scenarios. Apart from the measures, information was gathered on their effectiveness in reducing
emissions, and the time scale necessary for their implementation. The difficulty here was in
the packaging, and the potential number of packages. Originally the measures were grouped
into fifteen packages, but these were reduced to twelve (including two that were seen as being
more like supporting mechanisms - oil prices - or enabling mechanisms - carbon rationing).
Most of the packages had variants that were more suited to one image of the future than the
other.
These packages were then clustered together as scenarios to see whether the targets set in
each of the images could be reached. In this study an additivity assumption was used, namely
that the savings from each package were supportive of others. This assumption gives an
optimistic view of target achievement, and it would be useful to explore non-additive effects,
synergies and rebound effects in implementation (see concluding comments). The final stage
was then to establish the sequencing of implementation, so that the targets set for 2025 in
each image would be achieved - these are the policy pathways.
The packaging process was very fruitful as measures could be combined and efforts made
to ensure their impact was made more effective. To achieve substantial reduction in emissions
requires combinations of mutually supporting policies, often involving a variety of stakeholders.
Individual policies will certainly not take us far down the lower carbon route. Combinations
(together with the supporting soft measures such as awareness raising) can help control for
rebound effects, where individual reductions in emissions are in turn increased as people travel
further, thus negating some of the benefits. Many of the packages are extremely interrelated,
and this includes the technological options, such as low-emission vehicles, as they require
supporting behavioural change such as adapted consumer buying preferences towards low
carbon vehicles.
The potential carbon savings were calculated through the estimation of the reductions in
travel and/or change in mode share, and these figures were obtained from a wide range of
empirical studies and commissioned model runs. The modelling is developed to allow
quantification (in CO2 reduction terms) of the potential impacts of different scenarios. A range
of data sources are used, including commissioned runs from the strategic highway model for
(Department for Transport, 2008b), modal CO2 emission factors (Department for Food and
Rural Affairs, 2009) and London Plan (Greater London Authority, 2009) spatial planning
assumptions. The analysis proved to be enormously useful in working out how the targets set
could be achieved, in illustrating likely levels of change, and they also give an indication of
the importance of each package and their variants. The modelling hence proved critical in
providing some quantitative input to an essentially qualitative process.
