Scheme Appraisal for Highway Projects 67 The number of residential properties where noise levels within the assess-
ment year for the ‘with proposal’ option are 3 dB(A) lower than for the ‘do-
minimum’ option
The number of residential properties where noise levels within the assess-
ment year for the ‘with proposal’ option are 3 dB(A) higherthan for the ‘do-
minimum’ option.
Local air quality
Levels of both particulates PM 10 (in micrograms per cubic metre) and nitrogen
dioxide NO 2 (in parts per billion) are of particular concern. Firstly the roadside
pollution levels for the year 2005 are identified for both the ‘do-minimum’ and
‘with project’ cases. Then the exposure to this change is assessed using the prop-
erty count, with the diminishing contribution of vehicle emissions to pollution
levels over distance taken into account using a banding of properties. The pol-
lution increases of those dwellings situated nearer the roadside will receive a
higher weighting than increases from properties further away under this system.
Having separated out those parts of the route where air quality has improved
and where it has worsened, for each affected section under examination a score
for both PM 10 and NO 2 are obtained:
Particulates score =(Difference in PM 10 in 2005) ¥(weighted number of
properties)
Nitrogen dioxide score =(Difference in NO 2 in 2005) ¥(weighted number of
properties)
The final score is then obtained by aggregating the separate values
across all affected sections. This computation is done separately for each
pollutant.
In addition, the impacts of the proposals on global emissions are assessed
using the net change in carbon dioxide levels as an overall indicator. To achieve
this, the total forecast emissions after the proposal has been implemented are
calculated and then deducted from the estimated values for the existing road
network.
Landscape
NATA describes the character of the landscape and evaluates those features
within it that are deemed important by the decision-maker. The result is a qual-
itative assessment, usually varying from large negative to slightly positive, with
the intermediate points on the scale being moderately/slightly negative and
neutral. In situations where the scheme is unacceptable in terms of visual intru-
sion, the assessment of ‘very large negative’ can be applied.
Biodiversity
The purpose of this criterion is to appraise the ecological impact of the
road scheme on habitats, species or natural features. The appraisal summary