The topics of journey time reliability (JTR) and its evaluation in the literature were compared with current advice in Scottish Transport Appraisal Guidance (STAG). The latter seemed well up to date with the state of the art, and no major revisions were suggested. Both in STAG and in the literature, the accepted way of encapsulating the value of JTR changes is via the measure known as the reliability ratio (RR). This is discussed in some detail in the report. It has some weaknesses: it can be difficult to calculate, and can only be transported to other times and locations with great care. RR values have been calculated for both the freight and non-freight samples.

The results from the study will form part of the evidence for the next review of Scottish Transport Appraisal Guidance (STAG)