Starting up; early stages - Introduction to Environmental Impact Assessment - page 95

not usually required (outside “sensitive areas”). This is often referred to as the “traffic
lights” approach—red (mandatory), orange (indicative) and green (exclusive).
Table 4.1 Thresholds versus case-by-case approach
to screening: advantages and disadvantages

Advantages Disadvantages

Thresholds

Simple to use Place arbitrary, inflexible rules on a variable environment

(unless tiered)

Quick to use; more certainty Less room for common sense or good judgement

Consistent between locations May be or become inconsistent with relevant neighbours

Consistent between decisions within
locations

Difficult to set and, once set, difficult to change

Consistent between project types Lead to a proliferation of projects lying just below the

thresholds

Case by Case

Allows common sense and good
judgement

Likely to be complex and ambiguous

Flexible—can incorporate variety in
project and environment

Likely to be slow and costly

Can evolve (and improve) easily Open to abuse by decision-makers because of political or

financial interests
Open to poor judgement of decision-makers Likely to be
swayed by precedent and therefore lose flexibility

The DETR (2000), ODPM (2003b) give more detailed guidance on how screening is
carried out for most English and Welsh development projects.

4.4 Scoping—which impacts and issues to consider?

The scope of an EIA is the impacts and issues it addresses. The process of scoping is that
of deciding, from all of a project's possible impacts and from all the alternatives that
could be addressed, which are the significant ones. An initial scoping of possible impacts
may identify those impacts thought to be potentially significant, those thought to be not
significant and those whose significance is unclear. Further study should examine
impacts in the various categories. Those confirmed by such a study to be not significant
are eliminated; those in the uncertain category are added to the initial category of other
potentially significant impacts. This refining of focus onto the most significant impacts
continues throughout the EIA process. Good scoping has been shown to be a key factor in
good EIS (Mulvihill & Baker 2001, Wende 2002).