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Chapter 4
Data Preprocessing
4.1
Nationale Databank Wegverkeersgegevens (NDW)
De Nationale Databank Wegverkeersgegevens (NDW) or ”The National Data Warehouse for
Traffic Information” in English, is an organization that was established in 2007 and involves
various authorities working closely together to develop and maintain a traffic data database
for the road network of the Netherlands. NDW started serving traffic data about the most
important roads somewhere in 2009. Since then the databank has grown rapidly and currently
it ields more than 200TB of data from 20,400 measurement sites spread over 6,000 kilometers
of roads. Some of the main priorities are insuring high quality of the data and uniformity.
NDW ensures that all traffic data is entered properly into the historical database. If there are
any errors or delays in the real-time traffic data, they are being corrected before entered in the
database. Uniformity is achieved by presetting some rules and agreements about definitions
and calculation methods. This insures that the data coming from the different partners has
the same shape and is easy to use. We have to note that it does not mean that we have 100%
error free and available data.
NDW provides two types of information: traffic information and status information. Each
measuring site collects data every minute and then made available to the users in around 75
seconds. Traffic information includes:
• Traffic flow: the number of vehicles that pass a measurement site within a certain period
of time;
• Average speed;
• Realized or estimated travel time;
• Vehicle class - derived from the length of the passing vehicles.
All the accumulated real-time data is saved in the historic record and is thus is available for
later use and consultation.
The status information refers to the availability of a certain road:
• Road works and event-related traffic measures on virtually all the roads in the Netherlands;
• Reports of congestion, accidents and incidents on all the national roads;
City Traffic Visualization
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