Introduction real-time traffic data (AVG)

Introduction real-time traffic data (AVG)

Introduction

As far as AVG (real-time traffic data) is concerned the NDW periodically (delivery no later than 60 seconds after the measurement minute) provides data based on the more than 33,000 measurement locations in the Netherlands. At the moment this concerns the following types of data:

  • Flow
  • Speed
  • Travel time
  • Queues

Flow and speeds are measured at measurement points, and travel times are measured across measurement sites. The location and configuration of these measuring points and measurement sections are described as configuration data AVG in the so-called measurement location table. This measurement location table is updated every day at 13:00 hours and is made available as open data on opendata.ndw.nu as measurement_current.xml. The update is also ready with the necessary adjustments for the next day (measurement.xml), but for a receiving party this file is not relevant.

The Configuration data are therefore supplied separately in addition to the periodically supplied data on speeds, flows, travel times and queues. These files therefore contain a reference to the configuration data. For the coding of the configuration and of the periodically supplied data, choices were made in the Dutch DATEX II profile. These are explained below and in the various examples in the data services.

Configuration data

The configuration file for the AVG contains the following information for all locations where it is measured:

  • Measurement location configuration
  • Location reference for the measurement location

For queues, specific queue-related information has been added with an extension within the Dutch DATEX II Profile (see also the dataservice speeds and flows).

Measurement locations

For all measurement locations in the configuration file, the following generic data are always described:

  • Measurement location reference
  • Version of the configuration
  • Measurement technology used
  • Calculation method used

In addition, specific properties and the location reference are described for each type of measurement location. As described above, the AVG has two type of measurement locations for which a location reference is included:

  • measurement points (or combinations thereof) where measurements (flow, speeds, queues) are taken at a cross-section of a lane
  • measurement sites where measurements (travel times, queues) are taken between two cross-sections of the carriageway (or in some cases of the lane or lanes as well)

An overview of both types of measurement locations and an example of how the measurement location configuration and location reference have been registered according to the Dutch DATEX II profile.

For more information on the construction of the MeasurementSiteTablePublication you can click here.

Location References for real-time traffic data (AVG)

In the location reference for real-time traffic data (AVG), it is only allowed to use VILD points. For speeds, flows and travel times, only so-called point-location types can be used. These are characterized by a type designation starting with the letter P, followed by a numeric designation.

Warning

All point-location types are allowed except: P2.1, P3.3 t/m P3.12, P3.15, P3.18, P3.20 t/m P3.27, P3.29 t/m P3.37, P3.46, P5.0 t/m P5.5.

For queues, this means that this information always relates to a road location provided with a system that regulates traffic, not on a motorway. Therefore, the queue must always be defined with one of the following point-location types:

P1.11 Crossroads
P1.12 Junction
P1.3 Exit sliproad
P1.9 Roundabout
P3.1 Tunnel
P3.2 Bridge
P3.40 Aqueduct
P3.41 Locks
P3.43 Railroad crossing
P3.45 Ferry

Periodically supplied data

Over the locations that are included in the configuration file, measurement data is supplied periodically. These data consist of the following items for each measurement location for which data are supplied:

  • Reference to the configuration file
  • (Optional) temporary deviation from measurement location configuration
  • Measured data

Examples of this can be found in the various AVG data services:

Data exchange and DATEX II

The traffic messages are exchanged using the DATEX II standard, the European standard for registering and the exchange of traffic data. The DATEX II class D2LogicalModel is used for this. For the AVG data services, both Push (the supplying system initiates the transmission of data) and a Pull (the receiving system initiates the dispatch) mechanism is available. More information about system interfaces and the DATEX II class D2LogicalModel can be found in the Dutch Datex II Profile.

For the configuration and periodic data, the specialization (xsi: type) of PayloadPublication is used in the Datex II structure. Real-time traffic data is delivered in the MeasuredDataPublication (MDP). This publication is made up of all measurement locations included in the MeasurementSiteTablePublication. For each measurement location, a siteMeasurements element is filled with the unique identification of the measurementSiteRecord, the measured information and the time at which the measurement took place. If available, additional information is included such as the number of observations used to get to the value and the standard deviation of the current value. The MDP is a specialization of PayloadPublication, this specialization is indicated by giving the attribute xsi: type of element payloadPublication the value “MeasuredDataPublication”. The structure at the highest level is as follows:

../../_images/specialisatie_measureddatapublication.png

For more information about the elements in the above figure go to specialization MeasuredDataPublication.