1 Spatial Modelling of the Terrestrial Environment - Georeferencial

Modelling the Impact of Traffic Emissions on the Urban Environment 237
local road network. This, coupled with major growth in traffic using the strategic trunk
route network, has resulted in high levels of congestion on the region’s roads. The A14
Corridor, despite recent major upgrades, is now one of the most congested roads in the
country.
Consequently, the county faces a number of environmental problems that need a
solution. First, the section of the A14 Corridor between Huntingdon and Cambridge (see
Figure 11.2) experiences particularly high levels of traffic and congestion and as a consequence
is a significant source of emissions. Commuting from the villages in the corridor
to Cambridge has similarly brought about a growth of emissions from the adjacent minor
roads. The enormous growth of commuting to Cambridge and to a lesser extent, Huntingdon,
has also led to peak-hour congestion in both of these towns and inevitably this has
brought about an associated increase in traffic emissions. Despite this general pattern of
growth, the last County structure plan also had to deal with problems of rural stagnation
and contained policies to try and promote economic development in the rural, fenland areas
of the County between Cambridge and Ely.
For the purposes of the modelling exercise, a reference case was thus designed to represent
the actual situation observed in the area over the last decade. Model inputs were based on
local authority development assumptions, which aimed to preserve the Cambridge Green
Belt and allocate most land for housing in the market towns and larger villages. Some
housing development was permitted within Cambridge and a new village at Cambourne
was allowed some 15 km to the west of the City. Industrial development was confined
to existing sites and office development was concentrated in Cambridge, the peripheral
science parks and the main market towns. Retail development was mainly focused on
existing town centre sites. The number of jobs by employment sector and the total number
of households were constrained to Cambridgeshire County Council figures. No large-scale
transport improvements were modelled because there had been few significant changes
during the study period.
The alternative ‘policy case’ scenario was designed with the benefit of hindsight and
aimed to examine what might have happened if a very different planning approach based
on sustainable, albeit draconian policy decisions had been taken in the late 1980s and early
1990s. In general, the overall amount of development was kept to the same levels as in
the reference case scenario for comparability. However, the aim of the alternative scenario
was to focus most new development along the main rail corridor which runs from the north
east of the study area, through Littleport, Ely, Cambridge and on to London adjacent to
the A10 trunk route (see Figure 11.2). A new town was developed adjacent to the railway
at Waterbeach with both housing and employment uses. In addition, existing business and
residential sites throughout the corridor were expanded. Accompanying transport investment
was assumed to be focused on improved rail and feeder bus facilities within the A10
corridor. Specific transport improvements included new railway stations on the existing line
at Stretham and at the Science Park, near the A14 North of Cambridge. Access and waiting
times at all stations in the study area were improved to reflect more frequent services and
some rail journey times were also improved for villages close to Cambridge along the A10
to both the north and the south.
It is important to emphasize that the policy case package was not one that could have
been achieved in practice for a number of reasons. First, it ignored the inertia of previous
policy and effectively began with a ‘clean sheet’. Second, it is doubtful whether the package