Incident Detection
Technical Sheet No.7
Improving safety
Idris® Technology has developed an Incident Detection system which tracks vehicles on a multi-lane road and alerts traffic managers in the event of a stopped vehicle or exceptional incident. This is done entirely with loops below the road surface, avoiding the need for any overhead furniture. Trials have shown the effectiveness of this solution in all traffic conditions and weather scenarios.
Idris IDS:
The Idris Incident Detection System (IDS) consists of a group of outstations spread along the roadway, each responsible for monitoring a loop site, i.e. inductive loops arranged as one loop pair per lane at that point. Various algorithms are used to characterise the traffic and detect anomalies, which trigger alarm messages to a Higher Level System (HLS).
The IDS provides four broad categories of information:
- Alarms, which notify the occurrence of exceptional events on the highway
- Traffic information, sent at regular (configurable) intervals
- Vehicle data, which consist of records generated each time a vehicle passes over a loop site
- Status, which provides information regarding the roadside equipment, either on events or when requested by the HLS
The Single Stopped Vehicle (SSV) algorithm:
The core of the IDS is the Single Stopped Vehicle (SSV) algorithm. Its primary objective is to detect stopped vehicles in high-speed, free-flowing traffic - a situation in which accidents tend to be most serious. When the first outstation detects a vehicle, it sends a message containing relevant vehicle data to the next downstream outstation. This next outstation will expect the vehicle to arrive within a certain time window. If it does, the outstation will inform the following one and so on. If it does not, it is likely that the vehicle has stopped between the two outstations and an alarm is raised. This is a simplification of the actual processing, which needs to keep a virtual map of all vehicles transiting each outstation pair. The IDS is able to detect and track vehicles straddling lanes and changing lanes between outstations.
Alarms:
Alarms are associated with the carriageway, the outstation and the lane number and, where applicable, provide the data for the relevant vehicle.
Single Stopped Vehicle (SSV)
This alarm is raised when a vehicle which was detected by an upstream outstation fails to be detected by the current one. The implication is that the vehicle has stopped somewhere between the two sites, either on the running lanes or the shoulder.
Extra Vehicle
This alarm is raised when an unrecognised vehicle is detected at a site, i.e. the vehicle was not detected by the previous outstation. This would normally be a previously stopped vehicle rejoining the traffic.
Slow Vehicle
This alarm indicates a vehicle was detected at a speed significantly below the current average speed of other vehicles on the highway. This is in itself a dangerous condition and may frequently indicate the vehicle is about to stop.
Reverse Vehicle
Any vehicle moving in the wrong direction on a highway is a hazard and an alarm is generated immediately.
Slow Traffic
This indicates the average speed of the vehicles has fallen below a pre-defined threshold at the site. The cause will usually be congestion. This will also happen upstream from an incident, in which case it will probably be followed shortly by a Queued Traffic alarm.
Queued Traffic
A Queued Traffic alarm is raised to indicate traffic on that lane is showing shock-wave or start/stop behaviour. This is usually due either to excessive congestion or a downstream incident.
Status
Status messages are used to inform a HLS of equipment status and SSV algorithm status, such as: Operating; Off by command; Degraded; Failed.
Traffic information:
Traffic information messages provide data collected over configurable time periods:
- Traffic flow in vehicles per hour (on this lane) over the last time period.
- Average vehicle speed over the last time period.
- Presence of vehicles on the shoulder or in an ERA.
- Currently active alarms. This includes the number of active SSVs for that lane, Slow Traffic and Queued Traffic indications.
- Traffic count, in vehicles, over the last time period. For added flexibility, two data collection intervals are defined - one for the traffic count information and one for the flow, speed and alarm status information
Vehicle records:
Every time a vehicle crosses a loop site, a record is generated including such information as:
- Carriageway, lane and direction
- Vehicle length and speed
- Date and time of the occurrence and site occupancy time
Other data may easily be obtained from this information, such as the headway between consecutive vehicles.
Traffic information message processing:
This provides a real-time picture of the highway conditions such as average speed and vehicle count. This can be used to warn of congestion, and support decisions, for example, to open a shoulder to traffic.
Vehicle processing:
Although the vehicle records are strictly a by-product of the incident detection processing, they provide significant opportunities in longer-term traffic management. These include:
- Reconstitution of the highway scenario immediately prior to an accident, for legal support (Idris is accurate enough for speed enforcement)
- Monitoring of traffic volumes and speeds at any level of detail (seasonal, weekly, daily, hourly, etc.) for future highway expansion planning.
- Monitoring of traffic patterns (lane changes, speed variations) to support traffic management strategies both for day-to-day congestion management and scheduling of maintenance procedures.
- Analysis of motorists' behaviour in diverse situations (free flow, moderate congestion, congestion and as a shock-wave of an incident propagates back along the highway).
- Vehicle records can be used real-time, when maximum information is needed at the Control Centre, or, once stored in a database, can be analysed at leisure by even the most time-consuming algorithms.
Conclusions
By providing a comprehensive set of highly accurate data, in a flexible manner, the Idris Incident Detection System enables safe and efficient administration of highway sections where traffic levels are reaching capacity. The following areas are addressed:
- Rapid response to events on the highway
- Day-to-day traffic administration
- Support for legal issues (reconstitution) if accidents occur
- Long term congestion and capacity expansion planning
- Deep off-line analysis of traffic behaviour
Idris uses only inductive loops below the road surface to achieve this, improving reliability and reducing whole-life cost.
The Idris Technology is protected by one or more of the following patents:![]()
EP0879457, USA 6345228, 6483443 and 6337640
Registered Patents also include but not limited to European Countries, Brazil, Mexico, Canada & Australia.
Idris® is a registered trademark of Diamond Consulting Services Ltd.
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