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Data collection

Until 1985, home interviewers handed out journey diaries that they would later come to collect and check. In these journey diaries, respondents enter their journeys for 1 day.

From 1985 onwards, the households are recruited by telephone after having received a written announcement. During this telephone conversation, the household details are registered and agreements are made about filling in a journey diary. Each member of the household receives an own journey diary. Up to 1994, only those older than 11 years old had such a diary; since 1994, the journeys of children younger than 11 are also registered.

For ‘multiple journeys’, i.e. those with many departure and arrival addresses (e.g. doctors on a round of visits), only the total distance travelled, mode of transport, and purpose were registered.

In addition the respondents complete data about the vehicles they use, including bicycles, mopeds, and slopeds (lighter and slower mopeds), so that the NTS offers information about the total vehicle possession of individuals and households.

Since 1999

In 1999, the research method was altered drastically. The main reason for this was the falling response, from 50% to 35%. The New NTS is based on the German Neu KONTIV Design (NKD). It is designed as a simple, written survey, with a telephone conversation to motivate the respondents, and possibly follow-up surveys for more detailed questions per subgroup.

One of the biggest differences with the old NTS is that diaries are sent first, after which telephone calls are made to motivate people to fill in the questionnaire and journey diary.

If a household has not yet filled in and returned the questionnaires for the fill-in day, a telephone call is made exactly a week later. Telephone and written reminders are carried out to a maximum of 4 times.

Households without a telephone receive the questionnaires, but do not get any support from the interviewers. They receive reminder letters from CBS after one and after two weeks if their questionnaires have not been received. At the third reminder (after three weeks), new questionnaires are sent. Finally, after four weeks, if necessary, a fourth reminder is sent.

Since 1999, use.

The most important changes that have been made in 1999 in the new design for collecting data are:

• respondents are drawn from the Borough Basic Administration instead of the Geographic Basic Register;
• simplified questionnaires;
• households without a telephone or with unlisted telephone numbers are also recruited;
• respondents are motivated during a telephone conversation;
• follow-up surveys by telephone.
• with regard to the questionnaire's contents, a distinction is no longer made between a moped and a sloped; it can only be filled in on the dotted line. This has resulted in many respondents filling in 'scooter' without knowing if they meant a moped or sloped. For respondents of older than 35 years old, a sloped is filled in and for those younger than 35 years old, a moped.

From 1999 onwards, the response has been about 70%. Although we carried out a trend break correction, not all data after 1998 can be compared with the 1985-1998 period. One will just have to be careful when interpreting the developments.

Questionnaire

The questionnaires are as simple as possible, so as not to discourage the respondents. Follow-up surveys in small subgroups are carried out for additional information.

The basic questionnaire consists of:

• A written household questionnaire
• In this, the household details and background characteristics of all individuals of 6 years and older are collected. There are also questions about the vehicle possession.
• Individual questionnaires
• In these, every person of 6 years and older is asked about all journeys made on the fill-in day.

Follow-up surveys

Some of the households who have responded are once more approached by telephone to collect extra information. This happens among/if:

• households with children younger than 6 years old,
• questionnaires poorly/not filled in,
• public transport journeys,
• road crashes,
• journeys involving the use of more than one mode of transport.

There are no follow-up surveys among households without a telephone.