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Introduction

This page covers carriageway section allocation to a radar and coverage.

Coverage is where we have radar coverage for all or parts of a carriageway so we can track vehicles.

Section Allocation is how we have allocated sections of a carriageway to a radar for the sole purpose of gathering traffic statistics.

Contents

Coverage

There are four elements which control coverage; Range of the Radar, Contour Maps, Exclusion Areas and Radar Group allocation to a carriageway.

Range of the Radar

The range of the radar depends on the model deployed and is calculated by the Range Resolution x Range in Bins.

In the example below, there have been no constraints attached to the radar and so the full range of raw data (shown in bright green) is displayed within the pink boundary:

Radar Contour Map

The radar processes raw data far beyond the carriageway area, and this data is superfluous. Therefore, by creating a Contour Area, you prevent the steaming of unnecessary data.

In the example below, the range of the radar is still within the pink boundary, however, a Contour Map (displayed with an orange dashed boundary) has been created which limits the range of the radar to the area near the carriageway. The raw data from this Radar Contour Map can be seen in bright green:


Exclusion Areas

An Exclusion Area is the equivalent of a black hole to the system; everything within its borders is completely ignored. This is useful to have at a junction, or roundabout, for example, to prevent a car waiting to pull out being classified as a Stopped Vehicle.

In the example below, the Exclusion Area has been added in bright yellow, and this further limits the radar coverage. In the https://navtechradar.atlassian.net/wiki/spaces/TUN/pages/2362081381/Carriageway+Stats#Carriageway-Mini-Control, the Current Coverage of section 6 has been reduced by the size of the exclusion area to 99%:

Radar Group Allocation to a Carriageway

Finally, Radar Group allocation to a carriageway can effect the range of a radar.

In the example below, within a tunnel with two bores, there are two Radar Groups; one for each of the single carriageways. One is travelling east, and the other west. Using two different radar groups, the east radar will not report back any data from the west-bound carriageway and vice-versa:

Section Allocation

There are two sensor allocation modes; Nearest and All in Range. For more information including how to edit the sensor allocation please visit Radar to Section Allocation.

Nearest

This is the default mode. The section closest to a radar is allocated to only that radar for purposes of gathering traffic statistics.

In the image below there are two radar illustrated with the carriageway sections allocated to them. The range for the top radar is circled in pink, and for the bottom, circled in aqua blue:

All in Range

In this mode the radar will gather traffic stats from all sections within range of the radar. This means where radar have overlapping coverage then we will gather duplicate statistics for sections covered by more than one radar.

So in the image above, Radar 001 will not only gather stats for sections 1 to 11, but also for sections 12 to 20 as they are within the range of the radar. The second radar will gather stats for sections 12 to 25, and also for sections 1 to 11. This is of course subject to the limitations of contour maps for each radar. This means that without contour maps applied there would be duplication of stats for sections 1 to 20, which we do not recommend. This is why this mode is not set by default.

Allocation with Limited Coverage

If a radar has 1% or more coverage within a section, and it still qualifies as the nearest radar to the section (in Nearest mode), then that section can be allocated to that radar.

In the scenario below, Section 14 is just over the boundary of the radar range, but, the maximum range of the radar is still clipping the section and so the Current Coverage is greatly reduced at 1%:

Unavailable Radar

If a radar develops a fault or goes offline then the coverage and allocation statuses can change.

In this scenario there are a number of radar with Nearest Section Allocation Mode, situated along a carriageway, each with their own coverage, circled in the colour of the radar:

We are going to focus on three radar, each with a contour area (displayed with an orange dashed boundary). In the image below Radar 205 has a contour area which covers sections of the carriageway from 30 to 34:

Radar 206 has a contour area which covers sections of the carriageway from 25 to 30:

Radar 207 has a contour area which covers sections of the carriageway from 23 to 25:

At this point each radar is healthy, showing as three green dots along the carriageway:

The Carriageway Stats mini control confirms this with 100% coverage for the whole carriageway, and for Section 26 a healthy Coverage and Statistics Status:

However, if radar 206 fails then we would expect to lose coverage for sections 26 to 29, and because the system has a Sensor Allocation Mode of Nearest we would not expect that statistics for the sections 26 to 30 which have been allocated to Radar 206 to be available.

The system clearly shows that the sections of carriageway allotted to Radar 206 are compromised by the display of heavy dashed amber and red lines. The Statistics Status of section 26 is unhealthy (red) and the Current Coverage of the whole carriageway is showing a red bar as the coverage has dropped from the expected 100% to 92%:

We would still expect that there would be coverage for Section 30 as we have 100% overlap in the adjacent Radar 205, which has a contour area that covers this section. However, we would not expect stats for Section 30 as we are in Nearest mode, and that is why this section is highlighted in heavy amber dashed lines:

For All In Range sensor allocation mode, the implications for a radar failure are slightly different for coverage and section allocation; you would get duplication of stats.

The coverage status change is reflected in the ICD-001 Carriageway Statistics Report.

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