Sat navs: Sat nav live traffic

This Garmin model is guiding the driver away from the live traffic hot spots shown in red, onto a quicker route with the same final destination

Most sat navs these days have features beyond just taking you from A to B. One of the most useful is live traffic information sent directly and automatically to your sat nav device. This 'alerts' the sat nav of heavy traffic on your route ahead.

At the very least the sat nav will warn you of this, often giving more details of the delay and calculating a new estimated time of arrival for you. 

If you are lucky however and one exists, the sat nav will also find a new route around this traffic delay. It will ask you if you'd like to accept this new, faster route, or stick to the original one.

This live traffic information is available on most dedicated sat navs. It's also available on some mobile phone sat nav apps as an optional add-on.

Here, we take at a closer look at the two main live traffic systems.

TMC

TMC - Traffic Management Channel - is available on many cheaper dedicated sat navs. A TMC equipped sat nav picks up information from local radio stations via an antenna that is built-in or bought separately.

Usually only major roads, such as motorways and A-roads, are covered, while the information is sent and received every 15 minutes. If the congestion hot spot is a daily occurrence (as opposed to a tailback behind an accident), it may not be flagged.

Information can sometimes be delayed by poor weather conditions.

TMC is by no means a perfect solution to avoiding traffic, although it is a free service on most devices and it can sometimes help, especially if you are driving out of town.

TomTom HD Traffic showing a 1 minute delay 0.8 of a mile ahead

Live internet traffic

Newer traffic avoidance systems are live internet services offered by brands such as TomTom (HD Traffic) and Garmin (3D Traffic Live) on their mid-range and high-end sat navs. Increasingly sat nav apps on mobile phones are offering live internet traffic too.

Live internet traffic uses a built-in SIM card (inside the sat nav or mobile phone) to receive traffic information. This information is picked up by the sat nav every two minutes, giving you a better chance to avoid jams than with TMC.

The information is first of all collected centrally from a variety of data sources - these multiple sources are used to increase accuracy. It is therefore plotted to calculate traffic flow speeds, and therefore where traffic jams exist. 

Thanks to the mobile internet being able to carry more data than the radio signal that TMC uses, richer information covering B-roads as well as A-roads and motorways is sent to the sat nav. TomTom HD Traffic covers minor roads as well. 

Although not a foolproof way of avoiding jams, live internet traffic is a superior system to TMC.  For example, on one regular and well-known in-town test route we tried, it detected traffic ahead twice, re-routed and sent us off the main road and in to some small, unknown side streets, before guiding us back onto the main road further along, saving us time overall.

One problem of this system however can be a lack of mobile internet signal slowing down updates to more than every two minutes - but this is more of an issue in remote areas where the mobile internet signal tends to be weaker. 

Live internet traffic systems tend to be offered free for one year as part of a bundle of live services, but after that you'll have to pay to extend the service. On mobile phones it is usually an optional paid-for add-on that you can buy at any time.