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General Method of CAFT

The CAFT-surveys include the following procedures of data collection:

  • Road side interviews of lorry drivers at the major crossings of the entire Alpine arc.
  • Interviews of lorry drivers using Rolling Road at the Terminals.
  • Extraction from data bases of key national railway undertakings and additional surveys of other railway undertakings.



Road side interviews: General Features

  • The road side interviews are sample based. The total population of the sample is constituted of heavy goods vehicles crossing the interview points, which are located on all major routes relevant for the transalpine freight flows.
  • The total population of trips is known from traffic counts or toll statistics. In general, the survey points are located at places where at least automatic traffic counts are available. So the information on the total number of trips is indeed made available by non sample based measurements.


Road side interviews: Sampling
Sampling is done in a two-step approach:

  • First, the selection of sampling periods: Usually this is not done randomly but systematically, ensuring a representative distribution of the time periods over the seasons of the year, over the days of the week and over the time periods of the day. Organisational aspects also have to be taken into consideration in order to allow for a cost efficient performance of the survey and to be able to take specific conditions of the traffic flows into account.
  • Second, the sampling of vehicles during the survey period: Here, the aim is to select vehicles randomly from the undisturbed vehicle flow. However, a low burden on the drivers (minimum waiting times) and a homogeneous workload for the interviewer also have to be ensured. Thus it is not possible  to select e.g. every fifth lorry from the traffic flow, as in this case the inhomogeneous distribution of vehicles over time would cause periods of unacceptable waiting times for drivers and periods of inefficient work of the interviewer. In practice there is a rule applied ensuring quasi-random selection and efficient interviewing: each time an interview is completed, the next lorry is selected.

> The table with Sample Size Road Side Interview 2004 can be found here

 
Road side interviews: The interview
The Interview with the lorry drivers can be considered the key instrument for data collection. It is also the most critical factor in respect to the quality and the comparability of the survey. In principle, there is room for different interpretations of questions and answers both from the interviewer’s and the respondent’s (the driver’s) side. Thus, the design of the interview process, the tools supporting the interviewer and the training of the interviewer are important factors.

The interviews are carried out using handheld computer devices. Thus, the coding of questions like localities and commodities is done directly during the interview process at a high level of quality.
 
In this process of interviewing there are two ways of collecting the information:

  • Questions, which are answered by the driver, such as all information concerning the trip (loading and unloading place, route information, type and weight of goods) and specific items concerning the vehicle (year of construction, weights). 
  • Observations made by the interviewer, such as directly observable features of the vehicle (number of axles and shape, nationality of registration, information from the plate for dangerous goods…)

> A description of the “Interview - Process” (Example Austria) can be found here



Road side interviews: Expansion
The procedure of expanding reverses the process of sampling and takes into account non-randomly steps of sampling.

The expansion is implemented in two successive steps :

  • expansion of the interviews of each survey period to the total heavy traffic of this survey period. For the sake of this first step, a census of all heavy lorries crossing the survey point during the survey period is usually practiced, according to such parameters as the number of axles and the nationality of registration.
  • expansion of the results of the survey periods to the total traffic of the year, using information at hourly level by type of lorry available from the categories of automatic counters or from the toll classes. Some assumptions have sometimes to be made to fit with the scope of heavy lorries, whereas some additional information might be available in other cases, such as the nationality of registration of vehicles.

This procedure allows for a correction of biases caused by distortions in the selection process.


Road side interviews: National peculiarities
Whereas the key elements of the survey are harmonised between the Alpine countries, according to different administrative requirements, different traditions and different needs, there are some small differences in the three approaches:

  • The Swiss and the Austrian approach are more or less equal, also due to the fact that Austria adopted the methods from Switzerland in full scale, including the use of the same computer devices and software.
  • There are some differences in the practical administration of the survey in France: Wheras in Switzerland and Austria the surveys are carried out by a limited number of interviewers, having different survey periods on different locations, in France the interviews are planned at the same periods for all Alpine passes, which requires a bigger staff of interviewers.
  • France also added to a randomly selected part of the interviews a description given by the driver of the route chosen based on an A3 format map of major roads in Europe.
  • The French contribution to CAFT is embedded into the French National so-called ‘Transit’ survey, which aims both at covering all flows crossing mountainous borders of France and at covering as much as possible of flows transiting through France. As a consequence, in addition to Alpine passes at the border between France and Italy, the interviews also take place at the two main passes through the Pyrenean border with Spain, as well as at Bâle at the Swiss border to capture a significant part of the North-West/South-East transit flows not crossing the Alps or Pyrenees. At this additional survey points there is indeed more traffic concentrated  than at the French Alpine crossings. In 2004 in Austria an extension of the CAFT survey was also made to count transit traffic more comprehensively. But in the Austrian case, transit traffic is strongly dominated by Alpine crossing transport.  

 

Interviews at Rolling Road
The interviews of lorry drivers using rolling road are carried out at the Austrian and Swiss terminals, when lorries are accessing rolling road. The interviews are conducted by the staff of the transport agencies running the terminals, using paper based questionnaires. The questions are simplified compared to the road side interviews. The statistics on rolling road provide detailed data for grossing up.


Data collection from railway undertakings
The main railway undertakings are maintaining data bases on freight transport containing detailed information based on freight documents. These data bases are the key data source for CAFT railway data. Here, the limiting factor is not data availability or economical aspects of data collection but the privacy policy of the undertakings.

The data extraction contains :

  • recoding, e.g. from a very detailed classification of commodities to the chapters of NST/R or from the codes of railway stations to the geographic zoning system of NUTS, and
  • aggregation at a level, which allows for a good comparison with the road data.

 
As these commercial databases include all commercial activities, no sampling and grossing up is necessary.

Due to the liberalisation of the railway market, also enterprises other than the main national railway undertakings perform rail transport relations on Alpine crossing transport. Those enterprises are addressed separately.

copyright by BMVIT
Bundesministerium für Verkehr, Bau und Stadtentwicklung (Germany) Ministère de l'Écologie, de l'Energie, du Développement durable et de l'Aménagement du territoire (France) Ministero delle Infrastrutture e dei Trasporti (Italy) Bundesminsiterium für Innovation, Verkehr und Technologie (Austria) Eidgenössisches Departement für Umwelt, Verkehr, Energie und Kommunikation (Switzerland) Ministrstvo za promet (Slovenia) Directorate General Energy and Transport