Statistical Bulletin Transport Series Scottish Household Survey: Travel Diary 2009/2010

2. Introduction to the Scottish Household Survey and the Travel Diary

2.1 These statistics were obtained from interviews with a randomly-chosen adult in the household. The respondent was asked about their travel on the previous day. Each adult in the household had an equal chance of selection.

2.2 The results have been weighted to take into account differences in selection probabilities. Un-weighted sample numbers are given in italics. Data from two years is combined to obtain bigger sample sizes which allows for more detailed and reliable analyses.

2.3 Results are subject to sampling variability and care should be taken when interpreting year on year changes - confidence limits for the estimates are presented in Table 30 and should be considered alongside the data itself. A detailed background of the SHS methodology is given in the Appendix.

2.4 Although the total number of interviews was evenly spread across the week, this is not the case at Local Authority level. [Table 29] Day of the week analysis should therefore be treated with caution. Local Authority results are available separately on the Transport Scotland website here.

2.5 Table 10 contains statistics which underpin Scotland's National Indicator on congestion. More information on this National Indicator can be found here.

Methodological Changes - 2007 data onwards

2.6 A number of changes were made to the Travel Diary from 2007 onwards, as follows:

• Journeys less than ¼ mile or shorter than 5 minutes on foot are now reported - reduces under reporting of short (likely to be) walking journeys;
• Introduction of improved weighting system accounting for non-response bias.
• ¾ of the main SHS are now asked the Travel Diary element - previously all the households had been asked.
• Improvements to wording of questions - reduces under reporting of journeys.
• Improvements to data quality - e.g. duration of journey asked instead of calculated.

2.7 The main impact was a higher proportion of short, mainly walking, journeys with mode, distance and duration tables being most affected. For this reason, most time series comparisons mainly focus on those from 2007 onwards. Care should be taken when making time series comparisons prior to 2007. Further details of these changes are discussed in the Appendix.

Distance calculation

2.8 Travel Diary distances are calculated using the straight-line method (see Appendix) and therefore likely to be underestimated. A piece of work was undertaken to investigate the extent of the underreporting of Travel Diary distance - these were compared with GIS calculated distances for a sample of 2009 records. A short paper on the findings of this exercise will be published on under SHS data sources section of the website.