The traffic survey or traffic count is the determination of the number of vehicles or pedestrians crossing a road section or intersection in a given period of time. It is the basis for an economical and planned investigation of traffic connections.
Basically, one can distinguish between two types of survey:
- the census or traffic survey, which is concerned with the mere number of vehicles or persons,
- observation and questioning, which deals with behaviour.
Which of these basic types of survey is used depends on the results to be obtained from the survey.
In contrast to counting, observations and surveys cannot usually be automated. However, approaches to this already exist in freight transport, where data can be transferred directly from an EDP system. Such an IT system has been developed for the HGV toll in Germany.
Section 36(5) of the StVO allows police officers to “stop road users for traffic control, including roadworthiness checks and traffic surveys.”
Parameters and survey methods
A traffic survey can be carried out for various purposes, such as traffic statistics, road dimensioning or market research. Depending on the objective to be pursued, various parameters can be defined that are to be recorded in the survey. Possible survey variables in transport are, for example:
- individual characteristics such as trip frequency, trip purpose, travel time or choice of transport mode
- aggregated parameters such as traffic performance or traffic volume
- small-scale (microscopic) parameters of the traffic flow such as time gap, travel or cruising speed
- large-scale flow parameters such as traffic volume or traffic density, often also in temporal hydrographs
- passive and active road safety
- Attitudes and preferences
With no method can all variables be collected at the same time. For example, it is not possible to determine from the measurement data of a permanent counting station or a bicycle counter why people take exactly this route. The survey method must therefore be adapted to the research question. One can distinguish between several approaches:
- Measurement, e.g. of velocities
- Questioning in real or hypothetical situations(Stated Preferences)
- Qualitative data and participatory methods (examples: Qualitative interviews, critical incidents analysis, future workshop)
In object counting, people and/or vehicles are counted which are present in a certain observation area within a defined period of time. For example, the occupancy of a parking space could be recorded. In object counting, usually only counting is performed and no distinction is made between the individual objects to be counted.
In cross-section counting, people and/or vehicles are counted which pass a certain point of a road, the so-called (counting) cross-section, within a defined period of time. Automatic counting devices can also be used for this purpose. Here, a distinction is made either between the individual means of transport or between the types of vehicle. Combinations of both types are also possible.
An intersection survey is a small-scale form of stream survey that can be applied to simple road intersections. In this case, the cross-section count is additionally separated according to directions.
At intersections with a traffic signal, congestion lengths should also be determined as needed. Once congestion occurs, a count only represents the performance of the intersection approaches at the time of the traffic count. Congestion is not the vehicles that wait at “red” and can pass the intersection at the next “green”, but only the vehicles that cannot be processed at “green”, i.e. have to wait until a subsequent green phase.
Large-scale current survey or cordon survey
A large-scale flow survey records the traffic flows in an entire area. It usually consists of several cross-sectional counting points that form a closed cordon. Therefore, it is also called a cordon count. In addition to the number, the registration number of the vehicle is also noted or traffic participants are given a slip of paper. This survey can be used to determine which flows pass through, enter or leave the cordon.
A survey aims to identify past or planned transport activities and the reasons for these activities. In the process, road users are questioned directly. The results of all survey types are bundled and usually evaluated anonymously.
Questioning in the transport network
In transport network surveys, people, for example users of public transport, are interviewed at selected points or in the means of transport itself. This mainly involves the starting point and destination, but sometimes also the purpose of the journey and some socio-demographic information.
Interview at the place of activity or at the workplace
Surveys of this type take place in parking lots in the vicinity of recreational facilities. Surveys at the company serve to record commuter and commercial traffic. Here, too, questionnaires are often used, as in household surveys. Since freight transport in particular involves a sometimes very complex network of links, transport behaviour can usually only be recorded in part.
Structure of the survey
Several breakdowns may take place in the context of a transport survey. As a rule, the choice of means of transport is important. Furthermore, a distinction is made according to the object of transport. Here, a division into passenger and freight transport takes place.
In passenger transport, a distinction is made between individual and public transport. In addition to pedestrian and bicycle traffic, individual traffic also includes the use of cars, motorcycles, mopeds, scooters and trucks. Public transport includes journeys by taxi, bus, trolley bus, tram, light rail, underground, suburban railway, train, ship and plane.
In addition, a distinction is made according to the purpose of the journey; a distinction is made between private journeys and journeys within the framework of professional activity. Here, journeys to the place of residence, to work and training, for errands and in leisure time fall under private journeys. In contrast to the legal aspect, where journeys to and from the place of work are also considered to be work-related, here only journeys to perform work are considered to be work-related journeys.
The day is divided into two sections as part of a traffic survey. Daytime traffic takes place between 6:00 and 22:00 and nighttime traffic between 22:00 and 6:00. In the case of daytime traffic, the morning traffic between 6:00 and 10:00 and the afternoon traffic between 15:00 and 19:00 are often recorded separately. The traffic density is subject to strong fluctuations in the course of a day and depending on the area under investigation. As a rule, the highest traffic volume is to be expected at the following times:
|Residential area, roads on the outskirts of towns, roads outside towns||6:00-9:00 and 15:00-19:00|
|City centre, main streets in the city centre||7:00-10:00 and 15:00-19:00|
|Industrial park||6:00-9:00 and 15:00-18:00|
|Mixed area, school area||7:00-9:00 and 13:00-19:00|
A representative count should be conducted during the months of April, May, June, September, or October, and on a Tuesday, Wednesday, or Thursday (so-called normal value days) to minimize the influence of the weekend. In addition, days immediately before and after public holidays or at the beginning and end of holidays should be avoided.
Automatic recording methods
In addition to manual recording by instructed persons (with a counting device or tally sheet), there are various methods for automatic recording of traffic volume (traffic measurement):
- Traffic counting by means of induction loopspermanently embedded in the road surface
- Plate counting by means of counting devices temporarily mounted in the middle of the roadway, usually protected by an inconspicuous black plastic cover. These measuring plates are used for cross-section counting and record not only the number of vehicles but also their length and speed without contact via the change in the magnetic field. Some devices can also detect the temperature and moisture of the road surface.
- Side radar devices are also used for cross-section counting. A device installed on one side of the carriageway can detect the traffic of both directions at the same time in the case of a two-lane carriageway. However, as the volume of traffic increases, so does the counting error caused by vehicles that pass the side radar device at the same time and are thus only detected as a single vehicle.
Automatic measurements are often less accurate than manual ones. In order to estimate the accuracy of automatic measurements, it may be useful to perform manual comparison measurements. In Germany, traffic volume is determined or calculated on the basis of automatic and manual measurements.
- Traffic planning
- Traffic Physics
- Recommendations for traffic surveys – EVE. Forschungsgesellschaft für Straßen- und Verkehrswesen, Cologne 2012.
- B. Heuel-Fabianek Traffic Census 2004 at the Research Centre Jülich. Cross-sectional census, data collection year 2004, with example of a data collection sheet.
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– Collection of images, videos and audio files
- Automatic counting stations on motorways and federal roads. Federal Highway Research Institute
- Manual road traffic counting. Federal Highway Research Institute
- Hans-Jürgen Collin: Erhebungen zur Verkehrsnachfrage. In: Gerd Steierwald, Hans-Dieter Künne (eds.): Stadtverkehrsplanung : Grundlagen – Methoden – Ziele. Springer, Berlin/Heidelberg 1994, ISBN 3-540-40588-7, pp. 83-86, doi:10.1007/3-540-27010-8_5.
- Forschungsgesellschaft für Straßen- und Verkehrswesen (FGSV), Arbeitsgruppe Verkehrsplanung (ed.): Recommendations for traffic surveys (EVE). FGSV-Verlag, Cologne 2012, ISBN 978-3-941790-99-5, pp. 8-13.
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- Explanations on cross-section counting, Messtechnik Mehl; retrieved in February 2017
- Explanations on cross-section counting, Messtechnik Mehl; retrieved in February 2017
- see discussion of errors in the traffic report in the context of the Regenerstraße project-related development plan in Friedrichshafen, p. 10ff and p. 43; retrieved in February 2017