Statistical Bulletin : Trn/1999/2: Travel by Scottish residents: some National Travel Survey results

4. Notes and Sources
4.1 General points
4.1.1 In the tables, ".." indicates "not available", and "-" indicates "nil or negligible".
4.1.2 Totals may differ slightly from the apparent sums of their parts, where they have been calculated by adding up the "unrounded" values of their parts, and then rounding the results.
4.1.3 Averages per head: most of the statistics given in this bulletin are averages per head of population, with the base being the total population (including children, unless the context indicates otherwise). Of course, many of the quantities which are averaged will vary greatly from person to person: for example, there will be many people who do not travel on business at all, and others who travel thousands of miles on business.
4.1.4 Recent years for which figures are available: The first full calendar year of the present "continuous" National Travel Survey was 1989. Because the survey includes only 300 or so households in Scotland each year, the samples collected over three years have been combined in order to produce the results given in this bulletin. The figures for "1989/91" are therefore derived from the combined samples for 1989, 1990 and 1991; the figures for "1992/94" are based on the combined samples for 1992, 1993 and 1994; and those for "1995/97" are from the combined samples for 1995, 1996 and 1997.
4.1.5 Earlier years: The National Travel Survey was conducted as an occasional ad-hoc survey prior to the introduction of the current continuous survey. The figures for 1975/76 and 1985/86 are the results of the surveys carried out in those years. Because of changes over the years, only a few figures from the 1975/76 survey are available on the same basis as the figures for later years. As there was no survey for (eg) 1987/88, it is not possible to provide any figures for 1987/88.
4.2 The National Travel Survey
4.2.1 Sample design: Interviewers visit a randomly-chosen sample of households, which is spread across Great Britain. The "sampling frame", from which the sample is drawn, does not cover the whole of Scotland: most islands are excluded, with the result that, in 1996, the sampling frame did not include 2.2% of postal delivery points in Scotland. In order to reduce interviewers’ travelling time, the sample has a "clustered" design: in essence, each year, the areas (postcode sectors) to be visited are chosen at random, and then 21 households within each selected area are chosen at random. As a result, instead of each year’s survey covering a few households from each of several different parts of (say) the Borders, one year the sample might contain a number of households from (say) the town of Galashiels, the next year it might contain some from (say) a rural area around Duns, and the year after there might be no Borders households at all in the sample.
4.2.2 Collection of information: Interviewing takes place throughout the year. An interviewer visits all the sample households in a particular sample area over the course of a few weeks, and asks each member of the chosen households to complete a seven day "travel diary" covering all travel over 50 metres in distance. The details collected include the purpose of the journey, the method of travel and the length of the journey. The interviewers also obtain information about household members, such as their age, sex, working status, car access and driving licences (if any). In order to minimise the burden of completing the travel diaries, respondents only include walks of under a mile on the seventh day, and these "one day" results are subsequently grossed-up to represent a full seven days.
4.2.3 Households: A household consists of one or more people who have the sampled address as their only or main residence, and who either share at least one main meal a day or share the living accommodation.
4.2.4 Sampling variability: although the NTS’s sample is chosen at random, the people who take part in the survey will not necessarily be a representative cross-section of the people of Scotland. Because the NTS sample contains only 300 or so households in Scotland per year, because the response rate was about 72% in 1995/97, and because the survey has a "clustered" design, sampling variability may have a noticeable effect upon the NTS’s results for Scotland: for example, apparent large fluctuations between one period and the next in the NTS’s figures for rail usage may reflect the inclusion (by random chance) in the sample of more rail users (or of people who make greater use of rail) in some years than in other years.
4.2.5 Sampling limitations: The NTS's small sample size also limits the level of detail to which the results can be analysed. For example, the combined Scottish samples for 1995, 1996 and 1997 contained totals of only 307 bicycle journeys, 325 rail journeys and 440 taxi journeys. In each case, the number of journeys is too small for detailed analysis, particularly given the survey's "clustered" design. As well as the geographical clustering (see paragraph 4.2.1), the data on journeys are further clustered by being collected using seven day "travel diaries" (see paragraph 4.2.2). Therefore, for example, half of the 307 bicycle journeys in the 1995/97 sample could have been made by just a dozen people, if (in their seven days) each travelled to and from work by bicycle on five days, and each made another bicycle journey or two on each of the other two days, thus making a total of 12 or 13 journeys each during the seven days. The most that can be done with such small samples is to report the overall average numbers of journeys, distance travelled and resulting average journey lengths: there are too few cases to permit detailed analysis by (eg) the purpose of the journeys, especially as the journeys may have been made by a few sample members. In consequence, some modes of travel (like bicycle, rail and taxi) appear separately in a few of the tables, and are included in the "other" categories in the rest of the tables (those for which the number of journeys by those modes is insufficient to permit detailed analysis). For similar reasons, the extent to which some other modes of travel, and the purposes of journeys, are grouped may vary from table to table.
4.3 Definitions used in the survey
4.3.1 Personal Travel: The subject of the National Travel Survey is personal travel. This comprises travel for private purposes or for work or education, provided the main reason for the journey is for the traveller himself or herself to reach the destination.
4.3.2 Journeys in the course of work: Journeys made in the course of work are included provided they fulfil the requirement that the purpose of the journey is for the traveller to reach a destination. Travel to deliver goods, or to convey a vehicle or passengers (eg as a bus driver or taxi driver) is not covered. Nor is travel as conductors, guards or other crew of public transport vehicles, fire engines or ambulances, tractors etc. The survey also excludes travel in specially equipped vehicles used in the course of a person’s work (police patrol cars, AA/RAC repair vehicles, Post Office vans, etc); and journeys in course of work by people paid to walk or cycle, such as policemen on the beat, traffic wardens, leaflet distributors, messengers, postmen and roundsmen.
4.3.3 Leisure Travel: Travel for leisure purposes is normally included. Walking pleasure trips along public roads, including taking a dog for a walk and jogging, are within the scope of the survey. However, other journeys which are themselves a form of recreation are not (eg yachting or gliding, done for the pleasure of going in a boat or plane rather than to get somewhere). Travel by foot or by bicycle away from the public road is therefore excluded, such as travel across open countryside, in pedestrian precincts or parks. Children’s play is excluded.
4.3.4 Geographical coverage: The results given here are of travel within Great Britain by Scottish residents. They therefore include, for example, Scottish residents’ journeys within England, and exclude travel within Scotland by residents of England, Wales and countries outwith Great Britain. Only travel within Great Britain is included. Journeys to other places are included only up to the ticket control point at which the boat, plane or train using the Channel Tunnel, is boarded. Travel by road vehicle away from the public road is excluded, but travel on public roads in parks and on cycleways is included.
4.3.5 Journeys: The basic unit of travel, a journey, is defined as a one-way course of travel having a single main purpose. Outward and return halves of a return journey are treated as two separate journeys. A journey cannot have two separate purposes, and if a single course of travel involves a mid-way change of purpose then it, too, is split into two journeys. However, trivial subsidiary purposes (eg a stop to buy a newspaper) are disregarded.
4.3.6 Stages: A journey consists of one or more stages. A new stage is defined when there is a change in the form of transport or when there is a change of vehicle requiring a separate ticket.
4.3.7 Distance travelled: The length of any journey stage is the distance actually covered by the traveller (as reported by the traveller) and not the distance "as the crow flies".
4.3.8 "Series of calls" journeys: In order to reduce the burden on respondents, travel involving a number of stops for the same main purpose and using the same form of transport is treated as one continuous series of calls journey from the first such call to the last one. Only shopping and in course of work travel can be treated in this way. A doctor’s round would therefore consist of one journey to the first patient, one series of calls journey to the other patients and one journey from the last call back to the surgery or home.
4.4 Journey Purposes
4.4.1 Journey Purpose: The purpose of a journey is normally taken to be the activity at the destination, unless that destination is "home" in which case the purpose is defined by the origin of the journey. The classification of journeys to "work" are also dependent on the origin of the journey. A number of purposes, listed below, are distinguished
4.4.2 Commuting: journeys to a usual place of work from home, or from work to home.
4.4.3 Business: personal journeys in the course of work, including a journey in the course of work back to work. This includes all work journeys by people with no usual place of work (eg site workers) and those who work at or from home.
4.4.4 Other work: journeys to work from a place other than home or in course of work, eg coming back to work from going to the shops during a lunch break.
4.4.5 Education: journeys to school or college, etc by full time students, students on day-release and part time students following vocational courses.
4.4.6 Shopping: all journeys to shops or from shops to home, even if there was no intention to buy.
4.4.7 Personal business: visits to services (eg hairdressers, launderettes, dry-cleaners, betting shops, solicitors, banks, estate agents, libraries, churches) or for medical consultations or treatment, or for eating and drinking, unless the main purpose was entertainment or social.
4.4.8 Social or entertainment: visits to meet friends, relatives, or acquaintances, both at someone’s home or at a pub, restaurant etc; all types of entertainment or sport, clubs and voluntary work, non-vocational evening classes, political meetings, etc.
4.4.9 Holidays or day trips: journeys (within GB) to or from any holiday (including stays of 4 or more nights with friends or relatives), or journeys for pleasure (not otherwise classified as social or entertainment) within a single day.
4.4.10 Just walk: walking pleasure trips along public highways including taking the dog for a walk and jogging.
4.4.11 Escorting: used when the traveller has no purpose of his or her own, other than to escort or accompany another person; for example, taking a child to school. Escort commuting is escorting or accompanying someone from home to work or from work to home. Similarly, other escort purposes are related to the purpose of the person being escorted.
4.5 Modes of Travel
4.5.1 Main mode of Travel: Where a journey involves more than one mode of transport (eg first a bus and then a train), the main mode of a journey is that used for the longest stage of the journey. With stages of equal length the mode of the latest stage is used.
4.5.2 Car: includes light vans, Land Rovers and privately owned lorries.
4.5.3 Rail: includes both British Rail and London Transport Underground, but not any other rail service. Therefore the NTS includes the Glasgow Underground in its ‘other modes’ category.
4.5.4 Local Bus: includes all ‘local’ services, but excludes express services, excursions and tours.
4.5.5 Cycle: a cycle is any pedal cycle capable of use on the public road, but not children’s bicycles or tricycles that are intended as toys.
4.5.6 Other modes of travel: depending upon the context (ie depending upon which modes of travel are separately identified elsewhere in a table) the "other" categories may include some or all of the following - various "other" types of bus (works or school bus, private hire, express bus and tours and excursions), two-wheeled motor vehicles, motorcaravans, dormobiles, taxis/minicabs, domestic air travel, the Glasgow Underground, ferries and other private and public transport.
4.6 Other definitions and classifications used in the analyses
4.6.1 Household income: Household income is the total gross income of all members of the household, from whatever source, before deduction of income tax, national insurance or pensions contributions.
4.6.2 Household income quintiles: Because prices were rising at about 6 per cent a year throughout the early years of the continuous survey, and because household size and composition is not taken into account in the simple measure of household income, a new measure of household affluence — "real household income equivalent" — was devised. This is obtained by using household income equivalent scales to assign values to adults and children within a household — a technique used by the Department of Social Security when assessing Housing Benefit Scales. Total household income is then divided by the sum of these values in order to obtain the household income relative to a household consisting of just one married couple. These values are then deflated using the Tax and Price Index (TPI). The deflated values are then scaled so that the values for households average 100.0 in 1990. Quintile groups are then formed by assigning households to one of five groups in ascending order of affluence. (This process was done using the samples for Great Britain as a whole, so it is unlikely that any of the quintile groups will contain precisely 20% of the Scottish households in the survey.)
The values assigned to individuals within a household were as follows:
Head of household single parent	0.71
Other head of household	0.61
Wife of other head of household	0.39
Adult dependant	0.36
Unrelated adult (depending on number of adults in household)	0.38-0.43
Child aged under	2 0.09
Child aged 2-4 years	0.18
Child aged 5-7 years	0.21
Child aged 8-10 years	0.23
Child aged 11-12 years	0.25
Child aged 13-15 years	0.27
4.6.3 Work status: A person is described as working if in paid employment, or self-employed, during the previous week. Persons absent on holiday, on strike, temporarily sick, on study leave, maternity leave, or absent for similar reasons, are included. Sandwich students and students on vacation are excluded. Full-time work is over 30 hours a week. Part-time work includes any number of hours worked, however small, up to 30 hours a week.
4.6.4 Socio-economic groups: The groups shown in Table T are based upon the Registrar General’s classification of occupations:
I. & II. - Professional and Managerial: professional workers, employers, and managers, including self-employed professionals and farm managers;
IIIN. - Clerical: intermediate and junior non-manual workers, and personal service workers;
IIIM. - Skilled manual: including foremen of manual workers, own-account farmers and own-account manual workers;
IV. & V. - Semi-skilled manual and unskilled workers
Retired
Other economically inactive - includes those who are not looking for work.
The results for ‘all groups’ also include members of the armed forces.
Households are classified in socio-economic groups by the SEG of the head of the household.
4.6.5 Household vehicles: The term ‘car’ is used for all three or four wheeled vehicle with car body type, and also light vans, Land Rovers, dormobile and motorcaravans. Such vehicles are regarded as household cars if they are either owned by a member of the household, or available for the private use of household members. Vehicles used only for the carriage of goods, as public service passenger vehicles or solely for hire by other people are excluded. Hired or borrowed vehicles are included only if they were available to the household over the whole of the sample travel week. Company cars provided by an employer for the use of a particular employee (or director) are included, but cars borrowed temporarily from a company pool are not.
4.6.6 Access to cars: Three types of car access are distinguished in Table R for people in households with cars:
a. The main driver of a household car is the household member that drives the furthest in that car in the course of a year;
b. Other drivers are people in car-owning households, who have a full driving licence to drive a car, but are not main drivers of a household car. No account is taken of whether or not they actually drive a household car;
c. Non-drivers are all other people in car-owning households. They include children below driving age and adults with provisional driving licences.
4.7 Further Information about the NTS
4.7.1 DETR publications: DETR’s publications generally provide results for Great Britain as a whole, and do not show separately many statistics for Scotland or for other parts of GB.
DETR used to prepare an annual Transport Statistics Report on the results of the National Travel Survey, which was published by The Stationery Office. This series of publications has recently been discontinued, with the last of them being "National Travel Survey 1994/96".
Henceforth, NTS results will be included in a new series of publications called "Focus on Personal Travel", which will appear every third year. The first of these publications was "Focus on Personal Travel - 1998 edition", which included the report of the NTS for 1995/97, and can be purchased from The Stationery Office.
In the two years between editions of "Focus on Personal Travel", DETR will produce its own statistical bulletins giving updates of NTS data. Copies of these will be available from DETR (address below).
4.7.2 NTS Technical Report: The Office for National Statistics (ONS) publishes a Technical Report on the National Travel Survey, which includes details of the sample selection, fieldwork procedures, questionnaires and other NTS documents, response rates and data processing. Copies are available from ONS (telephone 01633 812 078).
4.7.3 Enquiries about the NTS: should be addressed to:
Spencer Broadley DETR Transport Statistics Zone 1/31 Great Minster House 76 Marsham Street London SW1P 4DR
Tel.: 020 7944 3097 FAX: 020 7944 2166