Social impacts may be ‘real’ or ‘perceived’ and measures must be able to cope with both dimensions. That is, a
so-called ‘real’ impact can be measured with objective data that verifies its existence. An example of this is the
level of traffic congestion which is a quantifiable outcome, although attribution to a particular cause of the traffic
congestion may be difficult to make. By contrast, a ‘perceived’ impact is purely a personal view of that impact
(Ap & Crompton 1998), although again, this view may be ‘contaminated’ by community discussion or media
attention, although Langford (2001) argues this view is far too simplistic.