Scottish Government

Title

Percentage of driver journeys delayed due to traffic congestion

Associated Targets

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.

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 year is 2006. Baseline value is 12.7%.

In 2010 10.5% of journeys were perceived to have been delayed by congestion, in line with the 2009 figure of 11.0%.

Although the proportion of driver journeys delayed due to congestion increased from 11% in 2003 to a peak of 14% in 2007, levels have been declining since. The 2010 figure (10%) is broadly comparable to 2003 congestion levels.

Methodology for Data Source

The Travel Diary sample was reduced to ¾ of the main SHS sample in 2007. This meant that the sample of respondents fell from around 14,000 to around 9,000 journeys (by car drivers). The smaller sample size is 2010 reflects the fact that less respondents undertook travel the previous day than in other years.

On the basis of the SHS's standard estimates of sampling variability, the 95% confidence limits around the latest change is +/- 1.1 percentage-points. However, the Travel Diary results may be subject to greater margins of error than this.

Data Ownership and Quality Assurance

National Statistics

Publication of Data

The latest data appears in Scottish Household Survey: Travel Diary 2009/2010 (Table 10).

http://www.transportscotland.gov.uk/analysis/statistics/publications/shs-travel-diary-results-previous-editions

Methodology for Recent Change Arrow on Scotland

Any difference within +/- 1.0 percentage points of last year's figure suggests that the position is more likely to be maintaining than showing any change. A reduction of 1.0 percentage points or more suggests the position is improving; whereas an increase of 1.0 percentage points or more suggests the position is worsening. See methodology note:

http://www.scotland.gov.uk/About/scotPerforms/indicators/methodology