Impact Matrices

From SEA.unu.edu/wiki

The impact matrix approach involves testing sub-components of a strategic action against a series of sustainability/environmental indicators. It was originally developed for use with land use plans, which typically consist of a series of statements ("policies") on e.g. location of housing, recreation etc.

The matrix has indictors in the columns and policies in the rows. One person - or ideally a team of several people with complementary skills - fills in the matrix cell by cell. For each cell, the team asks "is the impact of the policy on that indicator basically positive, negative or neutral?" and puts the relevant symbol/colour in the cell. However this is only the starting point for further discussion, possibly leading to re-writing of the policy, including:

• is the policy clearly written? what it will "look" like on the ground? does it say what it should say?
• if the policy is likely to have a negative impact, can this be minimised/mitigated?
• if the policy is likely to have a negative impact that cannot be mitigated, are other aspects of the policy so important that they override this negative impact? If so, the policy needs to be justified accordingly. If not, the policy may need to be deleted or given a major overhaul.
• can positive impacts of the policy be enhanced?
• where the impacts of the policy depend on how the policy is implemented, the symbol "D" (for "depends") may be added, along with a note about what would need to be done to ensure that the implementation is done "right".

Changes resulting from the appraisal are noted in the "comments" column. The point of the appraisal is NOT to fill in the matrix, but rather to ensure that the policies are as good as possible.

Example:

The matrix below uses two different approaches to filling in the cells

policy	indicators (impacts of policy on)				comments
	air pollution	land use	safety	quality of life, comfort
to promote Park-and-Ride at edge of city	better in city centre, worse outside	P+R land take; but better than providing more parking in city centre	fewer vehicle movements in built-up areas	fewer vehicles on city roads should speed up journeys for all: can QoL for P+R users be particularly improved?	clarify what "to promote" means aim to build P+R on previously developed land provide high-speed bus lanes from P+R to city centre
to increase parking charges in city centre	?	+	?	-	reduce charges for disabled people use extra revenue for public transport improvements

Advantages:

• Easy to use, does not require specialist knowledge
• Transparent
• Can be used as a technique to involve the public
• One of the few ways of appraising policies]
• Incoporates perceived impacts

Disadvantages:

• Subjective: the involvement of different people can lead to different results
• Involving several people (good practice) can make the process long-winded

Further information:

The UK good practice guidance on sustainability appraisal of regional planning guidance.