Goods traffic has become more and more important due to its high increase rates and its high specific emissions, not only in interregional traffic but also inside the settled area, where its effects on the traffic and the environment may cause conflicts. For the purpose of gaining a broader database for the planning of facilities and infrastructures with intensive goods traffic, the generation of traffic of existing plants shall be studied in detail. As a result characteristic figures, differentiated adequately, shall be quantified.
The aim of the research work was to record the characteristics of the delivery traffic and to derive indexes for the traffic planning for construction of facilities, large sites and development areas.
As the delivery traffic or goods traffic is very varied, the objective of the investigation had to be restricted. Goods traffic-flow from and to production, distribution and sales facilities was examined, whereby, in the latter case, delivery traffic for retail shops or for entire city centres was excluded.
The main focus of the research was road traffic, with journeys by heavy goods vehicles (lorries without or with trailers and semi-trailers) and delivery vehicles being taken into account. Rail traffic was not explicitly investigated, although its effects on road goods traffic were considered.
In order to collect the data, the following research methods were used: Literature research, meetings with experts, questionnaire surveys and additional automatic countings.
The literature research revealed a very heterogeneous image: There are some sources which systematically attempt to work out general indexes for traffic generation, but they are only partly comparable against each other (different levels of investigation, different definitions). Within the framework of the goods traffic models, the data were mostly unavailable at the desired level and instead were either greatly differentiated or greatly aggregated. Project-specific traffic generation rates can be derived from various sources, but it is not always easy to tell whether they
are representative or describe exceptions.
The meetings with experts formed the basis of the investigations. They represent the foundation on which the results of the literature research can be validated and commented upon, and they follow the margin of deviation of the indexes to be explained and the factors for above and below-average values of the indexes to be identified. An attempt was made to find companies from every branch being examined, i.e. Production, Sales and Distribution, who were prepared to meet with the research team for approximately one and a half hours. The meetings followed a semi-standardised procedure (set topics, open questions). Overall, 26 meetings were held with experts.
Based on the provisional results, the meetings with experts were accompanied, in consultation with the management committee, by a written questionnaire to a larger group of companies. The following features were asked about:
- Structural features such as branch membership, number of employees, area of the site, gross floor area and available traffic infrastructure
- Traffic volume of goods vehicles (road and rail) and distribution by vehicle type
- Temporal distribution of the traffic volume
- Estimate of the company's transport intensity
A random sample of almost 900 companies was drawn from the address database of the Swiss enterprise census using various criteria. The response rate of just 10 % was disappointing, but not really surprising after the relative difficulties in finding partners for the meetings with experts. Sadly, not all the returned questionnaires had been completed fully and/or plausibly, so that fewer data sets were available, depending on the question.
The expectation that, within the framework of the research, a series of useful indexes could be collected regarding delivery traffic, was partly realised. However, it became clear from each expert meeting that the number of criteria affecting the characteristics of the delivery traffic was much too large to be able to define differentiated indexes precisely. The written questionnaire did not fundamentally change this fact either.A very great variance was also revealed here which could not always be conclusively explained. A control question as to whether the respondents considered themselves to be very, averagely or less transport intensive revealed large discrepancies between the self-assessment and actual traffic generation.
Under these restrictions, ranges could be produced for the rates of goods traffic generation. The following table provides an overview of the available indexes and which parameters to use in which cases - i.e. what input information for what branch (if known).