Sat Nav Live Traffic Data – How Does It Work?

TomTom Start2 GPS satellite navigation unitUpdate: This page is now quite old, it was first published in 2011. For information about the latest live traffic services available to sat nav users I’d recommend my more recent posts:

One of the most popular and powerful features on today’s GPS satellite navigation devices is live traffic data. Many sat navs can now receive live traffic data about congestion on your route and reroute you onto a less congested and faster route.

Although TMC traffic announcements on FM radio have been around for years, current live traffic services are far superior and much more accurate. I don’t know about you, but I’ve never liked TMC much and have often found it to be a bit hit and miss in terms of accuracy.

Having recently reviewed two sat navs, I’ve now learned a bit more about how live traffic services work.

Where Does Live Traffic Data Come From?

First of all, you need to understand that if you have a sat nav with a live traffic information service, it will send live data about your geographic location and your speed back to sat nav HQ. This is done using a mobile phone device that is built in to your sat nav and is completely automated, although you do have to give your permission for it to happen – this feature can be switched off.

Data like this from sat nav users is just one of the sources of traffic information used by the big sat nav companies. Here are a few other examples:

  • Vodafone gathers data about the location and speed of movement of the mobile phones on its network. This data is then made anonymous and sent to TomTom for use in its HD Traffic service.
  • Reports from commercial traffic information services, like INRIX, which is used by Navigon
  • Information from public sector organisations. For example, the Highways Agency gathers a huge amount of traffic information from its network of cameras and road sensors on main roads throughout the UK (try
  • Data from telematics and navigation devices in fleets of lorries and taxis that are partnered with a traffic information service
  • Traffic news reports regarding road works, accidents and other similar information

Turning Traffic Information Into Sat Nav Routes

All of this information is processed by the sat nav companies’ computers and then overlaid onto road maps. It is then possible to work out which roads are congested and which roads are not. Some of this is just common sense, and some of this has to be deduced by comparing the information with the same data taken at a different time. All of this is done by computers.

For example, if lots of data comes in showing cars moving at 20mph on a section of the M1, there is obviously a holdup. Similarly, if cars are queueing for twice as long as usual at a major road junction, it is obviously more congested than usual. On the other hand, if a city centre road is running at the speed limit during rush hour, this might be a good alternative route for commuters stuck in nearby queues.

The final task is to try and create faster routes for individual drivers who are already on their journey. For some people, this will be impossible, but for many users, it will be possible to take an alternative route that may be longer but quicker.

This new routing information is sent back to each driver’s sat nav and offered to them as an alternative route. They can then choose to accept the alternative or carry on as they are.

Here’s a picture from Navigon that explains how its Traffic Live system works (click to enlarge):

Navigon Traffic Live - a diagram showing how the system works
Navigon Traffic Live explained – click to enlarge

Doesn’t This Just Cause More Traffic Problems?

You might say that routing lots of extra vehicles away from a queue and onto a quiet road will just result in two roads getting busy. However, I don’t think this will usually happen.

First of all, these systems do not create more traffic – the traffic is going to be there, whether it’s using a sat nav or not.

Secondly, it makes good sense to try and even out traffic distribution across as many roads as possible. It’s better (from a driver’s point of view) to be on a moderately busy road that’s moving steadily than to be sitting in a queue, not moving.

The feedback I’ve heard is that these systems work quite well and are a useful tool for business drivers. I can only see them getting more popular as traffic congestion continues to get worse – if I drove regularly on business, I would certainly consider getting a sat nav with a live traffic feature.

Do you use one? Would you recommend it? Let us know in the comments below.

4 thoughts on “Sat Nav Live Traffic Data – How Does It Work?

  • February 13, 2012 at 6:37 pm

    With ref to traffic diversions given by some satnavs including mine a Garmin Nuvi 1340 LMT can someone tell me how the ariel for this is fixed up, especially the circular disc which has no visible connection point, as there are no specific instructions given in the quick start manual.
    John R

    • February 13, 2012 at 7:18 pm

      Hi John,

      I’m not too sure about this – is the disc part of the traffic aerial or is it an alternative mount or something like that? I think a lot of the FM traffic receivers simply use the power cord as the aerial and don’t require any special positioning.

      Hope this is of some help.

      Cheers, Roland

  • May 30, 2019 at 4:47 pm

    But how does the device RECEIVE the information? Does that always come through the mobile data connection?

    • May 30, 2019 at 5:46 pm

      Yes, that’s right. Live traffic info will come through the mobile data connection.



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