How is the speed data captured?

  • Last Post 06 December 2018
chrisb posted this 30 July 2018

I would like some more information on how the speed and flow data is actually captured - is it at the specific site point location or an average over a section of road? What sensors are used to capture the speed? 


Thanks for the help!

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Shaun Ryan-Izzard posted this 31 July 2018

I can confirm that all data within WebTris is from specific site point locations.

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  • chrisb
chrisb posted this 31 July 2018

Thanks, are you able to provide more detail on how exactly the speed is captured and recorded?

Shaun Ryan-Izzard posted this 07 August 2018

That very much depends on the sensors themselves. We utilise both a number of sensory technologies, including induction loops embedded in the road and RADAR sensors on the roadside. As you might appreciate, each system gets the data in slightly different ways.

abrown068 posted this 30 November 2018

Dear Shaun,

Would be grateful for clarification here, we can appreciate that each system gets the data in slightly different ways:

1) What are those different ways please?

2) How much confidence can one have in the average speed?

3) Would be grateful for a clarification para on what the data contained in the "Fused Averaged Speed" field actually is, how is it calculated, what does it represent?


Shaun Ryan-Izzard posted this 06 December 2018


Firstly, can I just clarify a point. WebTris does not contain speed data. It is a resource for traffic flow data. This data is, predominantly, collected by one of two technologies.

1) induction Loops - a series of wire coils embedded into the road which generate a magnetic field. As a vehicle passes over it, that field is disrupted, and by the nature of this disruption, we can infer the type of vehicle.

2) RADAR - by "bouncing" radio waves off vehicles and recording the time it takes for these signals to return, the distance and type of vehicle can be inferred.

Each technology has its own unique "peculiarities", however, when such technologies are commissioned, every effort is made to ensure that these technologies are comparable. As always, should there be any specific site that is felt is "of issue", please do not hesitate in contacting us.

I hope this is of use