64 Highway Engineering
for those living near a road. Vehicle vibrations can also damage the fabric
of buildings.
Pedestrian, cyclist and community effects The severance of communities
and its effect on people in terms of increased journey time and the breaking
of links between them and the services/facilities used daily by them, such as
shops, schools and sporting facilities, are evaluated within this category of
impact.
Vehicle travellers This assesses the proposal from the perspective of those
using it, i.e. the drivers. The view from the road (scenery and landscape), the
driver stress induced by factors such as the basic road layout and frequency
of occurrence of intersections, are assessed within this category on the basis
that they directly affect levels of driver frustration and annoyance leading to
greater risk-taking by drivers.
Water quality and drainage This measures the effect that run-off from a
road development may have on local water quality. Installations such as oil
interceptors, sedimentation tanks and grit traps will, in most instances, min-
imise this effect, though special measures may be required in particular for
water sources of high ecological value.
Geology and soils The process of road construction may destabilise the
soil structure or expose hitherto protected rock formations. These
potential impacts must be identified together with measures to minimise
their effects.
Policies and plans This impact assesses the compatibility of the proposal
with highway development plans at local, regional and national level.Some of the above impacts can be estimated in quantitative terms, others only
qualitatively. The exact method of assessment for each is detailed within the
Design Manual for Roads and Bridges.
It is imperative that the environmental information is presented in as readily
understandable a format as possible so that both members of the public and
decision-makers at the highest political level can maximise their use of the infor-
mation. One such format provided for in DMRB is the environmental impact
table (EIT), a tabular presentation of data summarising the main impacts of a
proposed highway scheme. At the early stages of the highway planning process,
the EIT format can be used to consider alternative route corridors. As the
process develops, specific routes will emerge and the level of environmental
detail on each will increase. The ‘do-nothing’ scenario should also be consid-
ered as it defines the extent of the existing problem which has required the con-
sideration of the development proposal in question. In most situations, the
‘do-nothing’ represents a deteriorating situation. If the baseline situation is to
include localised highway improvements or certain traffic management mea-
sures, this option could more accurately be termed ‘do-minimum’. DMRB
advises that an EIT be constructed for all relevant appraisal groups. Three of
these are: