Estimates for percentage of journeys perceived to have been delayed by congestion (from the Scottish Household Survey), percentage of Scottish roads needing repairs and total vehicle kilometres driven on Scottish roads (published in [Scottish Transport Statistics](https://www.transport.gov.scot/our-approach/statistics#)). Estimates from the Scottish Household Survey are updated annually in [Transport and Travel in Scotland](https://www.transport.gov.scot/our-approach/statistics#42764) . For perceptions of congestion, respondents are asked as part of a Travel Diary to indicate where they felt which car journeys they have undertaken the previous day were delayed by congestion, and by how long. These congestion perception figures are a National Indicator in the Scotland Performs framework. The figures for 2017 are for the years 2015-2017 combined, for 2018 they are for 2016-2018 combined, 2019 are for 2017 to 2019 combined and 2021 are for 2019 to 2021 combined. SHS estimates are National Statistics and provide figures which are representative of households and individuals in Scotland annually. The SHS has an annual sample size of around 10,000 individuals and, since 2012, has operated with a fully unclustered sample design. Due to the Covid pandemic there was a smaller sample size for the SHS survey in 2020. We are therefore not be able to provide 2020 data broken down in as many ways as usual. For example, we are not able to provide data for individual local authorities. Local authority road network condition is assessed via the Scottish Road Maintenance Condition Survey, which is organised by the Society of Chief Officers of Transportation in Scotland on behalf of Local Authorities. This is carried out using a specialist contractor using vehicles accredited anually by the [TRL](http://www.trl.co.uk/). These vehicles are equipped with lasers and high-resolution cameras and record a variety of different road characteristics. The construction of the Road Performance Indicator was changed in 2007-08 to the current Road Conditions Indicator (RCI), which has each ten-metre stretch of road being assigned to one of three categories - red, amber or green depending on the overall road defect score. The survey aims to cover all local authority A roads in both directions every two years, all B and C roads in both directions every four years and a 10% sample of unclassified roads every year, with the RCI for unclassified road being calculated from four years' of combined data to give a rolling four-year indicator. Vehicle kilometres driven are calculated by the Department for Transport and are not National Statistics, providing only a rough indication of the likely volume of traffic on the roads. These figures distinguish between motorway, urban (an area with a population of over 10,000 as of the 2001 Census) and rural roads.
The Scottish Household Survey is not subject to scheduled revision. Revisions and corrections to previously published statistics are dealt with in accordance with the Scottish Government Statistician Group corporate policy statement on revisions and corrections - a copy of which is available on the Scottish Government website
Some tables include missing values. This is where the count on which percentages would be calculated is less than 50 and this data is judged to be insufficiently robust for publication.
Road network traffic, perceptions of congestion and road condition
A glossary of terms used in the Scottish Household Survey is available in the [annual report](https://www2.gov.scot/Topics/Statistics/16002).
The Scottish Household Survey complies with statistical disclosure control principles and the Code of Practice for Official Statistics. It is therefore not possible to calculate how many respondents gave a certain answer based on the results of this survey.
The Scottish Government conducts several major population surveys that are used to inform the policy debate in Scotland and in some instances the surveys can be complementary. The Long-Term Survey Strategy 2018-2022, of which the SHS is a central element, aims to ensure that the Scottish Government's population surveys continue to meet key information needs while maximising the analytical potential of the data they generate. A guide is available providing more information on Scotland's surveys.
Full details of the methodology and fieldwork outcomes for the Scottish Household Survey can be accessed on the [Scottish Government website](https://www.gov.scot/collections/scottish-household-survey/)
The SHS is designed to provide reliable and up-to-date information on the composition, characteristics, attitudes and behaviour of private households and individuals, both nationally and at a sub-national level and to examine the physical condition of Scotland's homes. It covers a wide range of topics to allow links to be made between different policy areas.