Data service Speeds and flows

Data service Speeds and flows

Introduction

The data service speeds and flows contain minute data about speeds, flows (flows often are subdivided by vehicle category) and queue information. This data is determined with point measurements and/or VRI’s. The delivery will take place no later than 60 seconds after the measurement minute. The data service contains the sum of the number of measured vehicles per lane per measuring point. The measurement period is one minute and the delivered value is a conversion of this minute data to one hour. Depending on the provisions of the road authority concerned, the output will show a distribution over vehicle categories.

The files are made available as open data on opendata.ndw.nu as trafficspeed.xml (periodic data regarding speeds, intensity and queues) and measurement_current.xml (configuration data of the measurement sites).

For more information about the structure of the MeasurementSiteTablePublication (measurement_current.xml) you can click here.

Structure and content

General

The data service Speeds and flows is part of the real-time traffic data (AVG). The specialization (xsi: type) MeasuredDataPublication from PayloadPublication is used for this purpose in the Datex II structure.

The main structure is shown in the figure below.

../../../_images/specialisatie_measureddatapublication.png

In the example below the use of the most important elements in this data service is explained.

Example

The file/soap message with the periodic data of travel times starts with the standard DatexII elements for delivery (see example XML below). The exchange element is used to exchange parameters related to the delivery, in this case the details of the supplier.

Element Explanation
exchange The element is used to exchange data related to the delivery
supplierIdentification describes the sending/delivering party
<d2LogicalModel xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" modelBaseVersion="2" xmlns="http://datex2.eu/schema/2/2_0">
  <exchange>
   <supplierIdentification>
     <country>nl</country>
     <nationalIdentifier>NLNDW</nationalIdentifier>
   </supplierIdentification>
  </exchange>
  <payloadPublication lang="nl" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="MeasuredDataPublication">
    <publicationTime>2017-08-09T08:52:40.008Z</publicationTime>
    <publicationCreator>
      <country>nl</country>
          <nationalIdentifier>NLNDW</nationalIdentifier>
    </publicationCreator>
    <measurementSiteTableReference targetClass="MeasurementSiteTable" version="960" id="NDW01_MT"/>
    <headerInformation>
      <confidentiality>noRestriction</confidentiality>
      <informationStatus>real</informationStatus>
    </headerInformation>
  ..
  </payloadPublication>
</d2LogicalModel>

In the above example, the attribute xsi: type of the PayloadPublication indicates that the specialization “MeasuredDataPublication” has been used. In addition, the following elements were used to provide extra information about the data delivery.

Element Explanation
payloadPublication Element contains the actual delivery of data
publicationTime Date and time the payloadPublication was created
publicationCreator Party that composes the publication
country Country of the composing party
nationalIdentifier Identification composing party
measurementSiteTableReference Reference to the measurementSiteTable
headerInformation Gives status and confidentiality information
confidentiality Confidentiality of the information provided
informationStatus Status of the information supplied

The actual travel time data can be found in the siteMeasurements element (see XML example below). The reference to the measurement location within the measurementSiteTable is done by means of the attributes of the measurementSiteReference element. In addition, the start time of the measurement minute is indicated in measurementTimeDefault.

Warning

The measurementTimeDefault element always indicates the start time of the measurement minute.

<siteMeasurements xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<measurementSiteReference id="PZH01_MST_0661_01" version="3" targetClass="MeasurementSiteRecord" />
<measurementTimeDefault>2017-11-15T14:11:00Z</measurementTimeDefault>
  <measuredValue index="1">
    <measuredValue>
      <basicData xsi:type="TrafficFlow">
        <vehicleFlow supplierCalculatedDataQuality="0">
          <dataError>true</dataError>
          <vehicleFlowRate>0</vehicleFlowRate>
        </vehicleFlow>
      </basicData>
    </measuredValue>
  </measuredValue>
</siteMeasurements>
Element Explanation
siteMeasurements Contains the measured traffic data
measurementSiteReference Reference to the measurement location included in the measurementSiteTable
measurementTimeDefault Start time of the period (measurement minute) for which measurement data are delivered

The traffic data for a measuring point is recorded in one or more measuredValue (main) elements. Each element refers (using the mandatory attribute index) to the corresponding measurementSpecificCharacteristics. The element itself has one mandatory element, measuredValue (subelement), and one optional element measuredValueExtension (not used in the example).

Element Explanation
measuredValue (hoofdelement) Traffic data for a measuring point
measuredValue (subelement) Subelement of measuredValue
measuredValueExtension Subelement of measuredValue

The measured value and the typing of the value itself is recorded in the specializations of the basicData element. In the case of the data service speeds and flows, the following specializations are used:

TrafficFlow Flow is coded through the TrafficFlow specialization
TrafficSpeed Speed data is coded using TrafficSpeed
TrafficStatus Queues are coded by means of the Traffic Status specialization

In the code example above it concerns the specialization “TrafficFlow” for code examples and the relevant elements of the other two specializations you can click through on the specialization names below.

Code example "TrafficSpeed"
Code example "TrafficStatus"

Within the basicData element, the vehicleFlow element is used to report the intensity of a measurement site. The vehicleFlow element inherits the attributes from VehicleFlowValue and DataValue. The vehicleFlow element expands its attributes with the vehicleFlowRate attribute. The attributes numberOfInputValuesUsed and standardDeviation are not used in this specialization.

In the event of a faulty measurement, the dataError subelement is used to indicate this. About how this is done click here. In addition, the reference value is included within the basicDataReferenceValue element in the measuredValueExtension. A typing of the reference value takes place using the referenceValueType element. In addition, the structure of basicData has been included under travelTimeData to indicate the reference value.

Below is an overview of the sub-elements of the measuredValue element with “TrafficFlow” as a specialization of the basicData subelement.

Element Explanation
basicData The TrafficFlow specialization of basicData contains the basic measurement data
vehicleFlow Indication of how the measurement data was determined
dataError Indicates that no, or no reliable data can be delivered by the measuring point.
vehicleFlowRate The number of vehicles that would pass the point for one hour based on measurement period.

De opbouw van de specialisatie “TrafficSpeed” (snelheid) van basicData kent de volgende elementen:

Element Explanation
basicData The TrafficSpeed specialization of basicData contains the basic measurement data
averageVehicleSpeed Element is used for reporting point speed of a measurement location
dataError Indicates that no, or no reliable data can be delivered by the measuring point.
speed Average speed detection point in KM per hour

The structure of the specialization “TrafficStatus” (queues) of basicData has the following elements:

Element Explanation
basicData The TrafficStatus specialization of basicData contains the basic measurement data
trafficStatus Element to report the queue of a measurement location
dataError Indicates that no, or no reliable data can be delivered by the measuring point.
trafficStatusValue Qualitative description of the flow of traffic
trafficStatusValueExtension The element contains additional elements that are required to describe a queue