Accredited official statistics

National Travel Survey 2022: Technical report chapter 2

Published 30 August 2023

Applies to England

Chapter 2: Background

The National Travel Survey (NTS) provides up-to-date and regular information about personal travel within Great Britain and monitors trends in travel behaviour. The Ministry of Transport commissioned the first NTS in 1965 to 1966, and it was repeated on an ad-hoc basis in 1972 to 1973, 1975 to 1976, 1978 to 1979 and 1985 to 1986. In July 1988 the NTS became a continuous survey (that is, fieldwork was conducted on a monthly basis starting in January and ending in December) with an annual set sample size of 5,040 addresses. This increased to 5,796 by 2001. In 2002 the annual set sample size increased to 15,048 addresses.

Since January 2002, the Department for Transport (DfT) has commissioned the National Centre for Social Research (NatCen), an independent social research institute, as the contractor for the NTS. NatCen is responsible for questionnaire development, sample selection, data collection and editing, data file production and building the database. The DfT is responsible for data analysis, publication, and archiving.

During 2011, DfT undertook a consultation exercise to review the methodology and content of the NTS for 2013 onwards. The review explored sample coverage, data collection methodology, interview question content and items recorded as part of the travel diary.

As a result of the review, in 2013 a number of items were removed from the interview questionnaire and the travel diary. In addition, the sample was restricted to cover England only with Scotland and Wales no longer included. The sample size for England remained at its previous level, meaning that the overall sample size for the survey was reduced. In 2022, the sample consisted of 12,852 addresses.

Following the onset of the COVID-19 pandemic in March 2020, face-to-face fieldwork was paused. The survey switched to a phone-based interview with an opt-in approach in May 2020, known as push-to-telephone (P2T) and this applied to the remaining months of the 2020 survey. In 2021, doorstep recruitment was reintroduced but with the interview remaining phone based, which was referred to as knock-to-nudge fieldwork (K2N). However for any points (also known as assignments) that could not be covered by an interviewer, the P2T methodology was used instead.

As with the 2020 and 2021 surveys, the 2022 survey method was altered in response to COVID-19. The 2022 survey made use of multiple methodologies: initially the K2N method was used for quarter one (January to March), and then face-to-face (F2F) was reintroduced for quarters two to four (April to December), with the option of a phone back-up (PB) for individual households where COVID-19 remained a concern. Additionally, both K2N and F2F were supplemented by P2T where necessary (that is, due to lack of available interviewer coverage). This had substantial implications for how the survey was completed and has been outlined in depth throughout this report.

This chapter describes the methodology for sample design, fieldwork procedures, data preparation and data provision for the 2022 NTS.

2.1 Uses of the NTS data

The NTS is one of DfT’s main sources of data on personal travel patterns in Great Britain. The survey collects detailed information on the key characteristics of each participating household and any vehicles to which they have access. In addition, everyone within the household is interviewed and then asked to complete a seven-day travel diary. The survey therefore produces a rich dataset for analysis with information recorded at several different levels (household, individual, vehicle, long-distance journey, day, trip, and stage).

Data from the NTS is used extensively by DfT to monitor changes in travel patterns and to inform the development of policy. The findings and data are also used by a variety of other organisations, including:

• other government departments (such as HM Revenue and Customs, HM Treasury, the Department for Environment, Food and Rural Affairs)
• university academics and students
• transport consultants, local authorities and voluntary sector organisations representing a wide range of interests including motorists, cyclists, the elderly, rural communities and children

Table 2.1 gives examples of the uses of NTS data.

Key results from the 2022 NTS are published by DfT in the statistical release National Travel Survey: 2022.

DfT deposit a non-disclosive version of the NTS dataset at the UK Data Service, which is available at the UK Data Service.

Table 2.1: Examples of the uses of NTS data

Uses
To help forecast future trends in road traffic as part of the National Transport Model in Road use statistics Great Britain 2016
To monitor the number of cycle stages per person per year for an indicator in the Department’s Single Departmental Plan
As an input into the Cycling and Walking Investment Strategy
To answer Parliamentary Questions and other Ministerial Correspondence, for example Roads: Accidents Bus Services: Commuters
As a possible supplement to rail demand forecasting models in DfT
In the development of the National Cycling Propensity Tool for DfT
For monitoring road accident rates amongst different road users, especially pedestrians in the Road accidents and safety statistics
To understand how people travel to the shops and the impact of home deliveries in the Why people travel: Shopping factsheet
To examine travel among different groups, such as elderly people and people with mobility difficulties in the Disability and travel: 2007 to 2014 factsheet
To get information about users of modes of transport, for example in the Motorcycle use in England factsheet
To produce free annual reports that allow analysis of changes in personal travel over time
To study how children travel to school and how this has changed over time, in the Travel to school factsheet
To provide analysis and advice for around 300 direct requests to the DfT statistics team per year

2.2 Review of fieldwork sequence

Historically, the NTS has used two data collection methods: F2F interviewing using computer assisted personal interviewing (CAPI) and self-completion of a seven-day travel record (issued as a paper diary). However, due to fieldwork restrictions in response to the COVID-19 pandemic, the traditional F2F interview and diary self-complete methodology was replaced with alternative phone-based approaches with interviewers completing the diaries on the respondent’s behalf (P2T and K2N).

F2F was only reintroduced for quarter two onwards of 2022 (with an additional phone back-up), having begun the year in quarter one with the same methodology that was in place in 2021, that being K2N fieldwork with P2T for points that could not be covered by an interviewer. K2N was no longer used after quarter one, but P2T remained in place for the remainder of the year. All approaches in force during 2022 used the same CAPI questionnaire, but in cases where F2F was not possible the interviews instead continued to be administered by telephone and the travel diaries were populated by interviewers collecting travel data from participants over the phone, as they had done during the pandemic years.

The overall sequence of tasks, from the initial sample selection to data analysis and reporting remained the same across K2N, F2F or PB and P2T:

1. Sample selection from the Postcode Address File (PAF).

2. Questionnaire development and fieldwork preparation.

3. Fieldwork.

4. Data transmission and documents returned by interviewers.

5. In-house data input and editing.

6. Quality checking.

7. Data checking using SPSS.

8. Data file production, variable derivation and imputation and delivery to DfT.

9. Data analysis and reporting by DfT.

Crucially, the overall sample selection remained the same, ensuring that the address sample was selected both robustly and randomly (see Chapter 3 for more details).

However, the fieldwork sequences differed slightly across the different methodologies. The K2N approach involved doorstep recruitment, with interviewers contacting respondents in-person, but conducting the placement interview over the phone and populating the travel diaries on the household’s behalf.

For those points (assignments) where it was not possible for an interviewer to visit, they were allocated via the P2T methodology. For these addresses, a letter was issued with a phone number and online portal link for households to ‘opt in’ to the survey. This meant respondents provided NatCen with a phone number and an appropriate time to contact them. These cases were then put together into points of a maximum of 10 cases and allocated to a remote interviewer. The remote interviewer then made phone contact with them and conducted the interview and diary completion via telephone.

The phone back-up (PB) option was used alongside F2F during quarters two to four. This fieldwork approach broadly followed the same fieldwork sequence as F2F with the exception of diary completion and carrying out the placement and pick-up interviews over the phone. For PB cases the diaries were populated by interviewers (in the same way as K2N and P2T), rather than individuals in the household. Likewise, interviewers were required to make two mid-week phone call checks for PB cases, mirroring the K2N and P2T approaches. PB was only used when F2F was not possible.

As noted later in this chapter, travel weeks were allocated using the ‘fixed travel week’ method for F2F and PB from quarter two onwards, whereas for P2T and K2N travel weeks were allocated using the ‘rolling travel weeks’ method. For P2T and K2N, this meant that the travel week always started the day before the interview. However, for F2F and PB the travel weeks did not follow this same pattern, and could be allocated to start up to two days before the interview, on the day of the interview itself, or several days after the interview.

Fieldwork sequence for F2F:

1. Sampled addresses issued to interviewers.

2. Advance letters posted (by interviewers).

3. Make contact at the address and organise interview.

4. Placement interview conducted in person, and travel diary placed with household.

5. Travel week starts, as per ‘fixed travel week’ allocation method.

6. One mid-week check (in person or by telephone).

7. Travel week ends.

8. Pick-up interview in person.

9. Return work and transmit data.

Fieldwork sequence for PB:

1. Sampled addresses issued to interviewers.

2. Advance letters posted (by interviewers).

3. Make contact at the address with the intention of arranging a F2F interview, but if concerns around COVID-19 were present then a telephone interview would be arranged instead.

4. Placement interview conducted via telephone, and travel diary task introduced to the household.

5. Travel week starts, as per ‘fixed travel week’ allocation method.

6. Two mid-week checks via telephone, with interviewer populating a couple of days of the travel diary at each check.

7. Travel week ends.

8. Pick-up interview via telephone including populating remaining days of the travel diary.

9. Return work and transmit data.

Fieldwork sequence for K2N:

1. Sampled addresses issued to interviewers.

2. Advance letters posted (by interviewers).

3. Make contact at the address and organise interview.

4. Placement interview conducted via telephone, and travel diary task introduced to the household.

5. Travel week starts one day before the placement interview, as per ‘rolling travel week’ allocation method.

6. Two mid-week checks via telephone, with interviewer populating a couple of days of the travel diary at each check.

7. Travel week ends.

8. Pick-up interview via telephone including populating remaining days of the travel diary.

9. Return work and transmit data.

Fieldwork sequence for P2T:

1. Advance letters issued centrally.

2. Respondents ‘opt in’ to the survey via the phone or online portal.

3. Households are grouped into points of a maximum of 10 cases and assigned to a remote interviewer.

4. Interviewer makes contact over the phone.

5. Placement interview conducted via telephone, and travel diary task introduced to the household.

6. Travel week starts one day before the placement interview, as per ‘rolling travel weeks’ allocation method.

7. Two mid-week checks via telephone, with interviewer populating a couple of days of the travel diary at each check.

8. Travel week ends.

9. Pick-up interview via telephone, including populating remaining days of the travel diary.

10. Return work and transmit data.

2.2.1 Sample selection

The 2022 NTS was based on a stratified, clustered random sample of 12,852 private households in England, drawn from the Postcode Address File (PAF), as was the case in 2021 (see Chapter 3).

2.2.2 The interview

Prior to 2014, interviewers were instructed to begin fieldwork at the start of the quota month. Travel week start dates were allocated within quota months, which ran mid-month to mid-month. However, analysis using 2012 data showed that this design led to an uneven spread of travel week start dates across the month due to interviewers following similar fieldwork patterns. In 2014 a new design was implemented to address this issue, whereby interviewers were assigned to start fieldwork on different dates across the month to ensure that the interviewing dates were more evenly spread.

Until 2016 interviewer assignments were distributed evenly across the year, with the same number of assignments each month. However, this approach meant that certain months, particularly February, were over-represented in the data. As such, in 2016 a small refinement was made so that interviewer assignments were allocated evenly across a quarter, rather than by month. When allocating assignments to quota months it is done in such a way a naturally representative sample is distributed for each quarter

The rolling travel week approach (whereby the travel week always started on the day before the placement interview) was introduced in 2020 to replace fixed travel weeks as it was not possible to control for the timing of the placement interview as part of the P2T methodology.

In 2022, the questionnaire and interview sequence remained similar to previous years, despite the changes to the data collection methodology brought about in response to the pandemic. Details of the methodologies used in 2022 is provided below.

Using the Knock-to-nudge approach (K2N) from January to March

For quarter one when K2N was the main methodology being used, the fieldwork procedure is outlined above in section 2.2 and began with the interviewer sending advance letters to the sampled addresses. These letters briefly explained the purpose of the NTS and mentioned that an interviewer would contact them. It also stated that each respondent would receive a shopping voucher if all household members completed the survey. Each member of the household received a £5 shopping voucher which was conditional on receiving diaries from all household members. From June 2004, a book of first-class stamps has also been included with the advance letter as an unconditional incentive and remained in place for the 2022 survey. To note that in 2022 the book of stamps contained four stamps compared with six stamps in previous years (this was due to the addition of a barcode).

Interviewers followed up the advance letter by making in-person contact with the household to arrange a placement interview and a travel week. This interview was conducted over the telephone with all household members if possible, however proxy rules were relaxed and allowed for one member of the household to complete the interview on behalf of the whole household. The placement interview gathered information about the household, its individual members, household vehicles and long-distance journeys that the household members had made in the last week.

At the end of the placement interview the interviewer completed the first two days (if possible) of the seven-day travel diary on behalf of the respondent, populating the diary with the travel that respondents had completed. In order to make this work as well as possible, K2N did not use a fixed travel week system, and instead used a ‘rolling travel week’ system (all travel weeks started the day before the placement interview was completed).

Following the initial placement interview, interviewers conducted two mid-week checks (again over the telephone) during the travel week to fill in more days of the diary on behalf of the household. This generally meant interviewers would complete a few days’ worth of the travel record for the respondents at each check. Finally, within six days of the end of the travel week, although ideally earlier, a pick-up interview was conducted, and the information about the remaining few days of the travel week was collected and entered by interviewers. The pick-up interview was also used to complete any outstanding sections of the placement interview and to check whether any key factors had changed since the placement, such as the purchase of a new car.

To ensure the project remained COVID-19 safe during the fieldwork process for K2N, the interviewer only visited the respondent’s household on one occasion (that is, for the initial contact at the address), with all other contact made via telephone.

Using the Push-to-Telephone (P2T approach), for any points that could not be covered by an interviewer

For the P2T approach, the interviewer and diary completion procedures were similar to K2N, as outlined above in section 2.2, however there were crucial differences. The interviewer did not send out the advance letter, which was instead dispatched by the NatCen Operations Department. This letter was altered with respect to the incentive offering and to the recruitment process. Additionally, addresses were sent a reminder letter containing a similar message to the advance letter. In these letters, households were informed that they would receive a £20 shopping voucher when they completed the second call with their interviewer. This conditional incentive was supplied as a single gift voucher to the whole household (regardless of household size), rather than the household members each receiving a £5 voucher individually, as was the case for K2N, F2F and PB. Additionally, the unconditional incentive of a book of stamps was not used for P2T.

The P2T letter also asked respondents to ‘opt in’ to the survey by providing their contact details via a freephone line or an online portal link. This was necessary given that the traditional doorstep recruitment process could not be used. Having opted into the survey, the addresses were grouped into points of up to 10 addresses, and these were then allocated to remote interviewers. These respondents were then contacted over the phone by interviewers to complete the placement interview.

Following contact from interviewers, the process for competing the placement interview, the seven-day travel record, and the pick-up interview over the phone were similar to the K2N mode, with interviewers completing the diaries and the use of the ‘rolling travel weeks’.

Using the Face-to-Face (F2F) with phone back-up (PB) approach from April to December

For quarter two onwards when F2F was the main methodology being used (with a phone back-up), the fieldwork procedure was the same as K2N initially, with respect to interviewers sending advance letters and visiting address to recruit people to the study. Interviewers were tasked with securing a F2F interview wherever possible, with the fallback option of offering a telephone interviewer (PB) for individual households where COVID-19 remained a concern.

However, the F2F or PB approach differed to the K2N methodology as the travel week generally started after the placement interview took place. The content of the placement interview was the same as the K2N. However instead of completing the initial days of the travel diary on behalf of the respondent, the interviewer instead explained and placed the seven-day travel diaries with all households, allocating a travel week using the traditional ‘fixed travel week’ method.

If respondents agreed to it, they were sent an automated text reminder on the morning of the first day of the travel week to remind them to start completing their diary. If there was a gap of more than a few days between the placement interview and the start of the travel week, interviewers made a reminder call or visit or delivered a reminder card to the household to remind them that their travel week was about to start. This was followed by a mid-week check call (either by telephone or face-to-face) during the travel week to check on the household’s progress in completing their diaries. For F2F cases the respondent completed the diary themselves, whereas in PB cases the interviewer populated the diaries on behalf of respondents over the phone.

Within six days of the end of the travel week a pick-up interview was conducted, and the diaries were collected and checked in the case of F2F interviews, and the remaining days of the diary populated for PB cases. The content of the pick-up interview was the same as for all methodologies.

2.2.3 Data input and editing

The CAPI data was transmitted back to the NatCen operations department, usually on the day after the pick-up call, and all paper documents were returned by interviewers by post. Once the documents had been received, a team of NTS coders booked the diaries into the system. They then coded, keyed and edited the travel diary information using the Diary Entry System. The contents of the CAPI questionnaire were edited and checked, and all interviewer notes examined. The interviewers were contacted if there were any queries that could not be resolved by the coders. If necessary, the interviewer re-contacted respondents to resolve any issues, although this would be rare given the burden on the respondents.

Quality checks were also made on selected interviewers on a rota basis and 10% of addresses were back-checked. Back-checking involved contacting participating households by telephone to ensure that they were happy with the way that the interview was conducted. The back-checking exercise did not find any systematic errors in the way interviewers were working for 2022.

2.2.4 Data file protection

The data were organised into different levels, namely:

• households
• individuals
• vehicles
• long-distance journeys (made in the seven days before the placement interview or before the travel week which ever date was earliest)
• journeys made during the travel week and days within the travel week
• stages of these journeys

Lastly, NatCen provided DfT with Primary Sampling Unit (PSU) level variables associated with each household, but which were not collected directly from households. See section 3.10 for further information about PSU-level variables.

2.3 Response

Only households classed as ‘fully co-operating’ are included in the response calculations. Based on this, a national response rate of 31% was achieved in 2022. For the K2N and F2F fieldwork combined (which includes any phone back-up cases), the response rate was 35%. The response rate for the P2T fieldwork was 9%. See section 4.12 for a definition of ‘fully co-operating’ and for full response details.

Overall, this is equivalent to an achieved sample rate (ASR) of 28%. The ASR includes those households classified as ineligible in the denominator.

Chapter 1 – Fieldwork approach in 2022

Chapter 3 – Sample Selection

Chapter 4 – Fieldwork Procedures and Response Rate

Chapter 5 – Data Processing

Chapter 6 – Weighting

Glossary

Appendices

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Further information

National Travel Survey statistics

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