Scottish Government

Title

Percentage of driver journeys delayed due to traffic congestion

National Indicator/Target

Reduce the proportion of driver journeys delayed due to traffic congestion

Brief description

This indicator monitors drivers' own perception of whether or not their journeys by car were delayed due to congestion, regardless of the journey type or the nature of the roads they travelled on.

It is not an actual figure for time lost due to congestion ( e.g. as in Transport Scotland's Congestion on Scottish Trunk Roads publication).

Strategic Objective(s) to Which Indicator Relates

This indicator informs progress in relation to the Wealthier and Fairer Strategic Objective.

Reductions in congestion enable shorter and more reliable journey times. This contributes to improved productivity and economic growth.

More Detailed Definitions

Definitions of Keywords

The figures are produced from survey information about journeys (or stages of journeys) that were reported as having been made as the driver of a car or a van.

In each case, the interviewer asks "was this part of your trip delayed due to traffic congestion?" No definition of traffic congestion is given, so respondents can interpret the term as they wish.

Evidence Source

Scottish Household Survey ( SHS), Travel Diary

Percentage calculated from survey responses

All else being equal, the smaller the percentage who say they were delayed by congestion, the more efficient and reliable the road transport network is.

It is a proxy for "efficient, reliable transport networks" as no single measure is available to capture overall performance.

Baseline and Past Trends

Baseline = 2006

Baseline value = 12.8%

Chart: Percentage of car driver journeys which were delayed due to traffic congestion

Source: Scottish Government - Scottish Household Survey, Travel Diary

Methodology

Each year's figure is based on a sample of around 14,000 journeys reported by car drivers. On the basis of the SHS's standard estimates of sampling variability, the "95% confidence limits" would be about +/- 0.6 percentage-points. However, there are reasons to suspect that the Travel Diary results are subject to greater margins of error than this.

Data Ownership and Quality Assurance

National Statistics

Publication of Data

Scottish Transport Statistics ( e.g. Table 6.9 of the "2006" edition gave figures for the years up to 2005). The printed version is scheduled to appear each December, and can be found via: www.scotland.gov.uk/transtat/sts

An updated version of the table, with a further year's figures, usually becomes available via that address each summer ( e.g. figures for 2006 appeared in August 2007).