So the incumbent RDS-TMC system has its drawbacks, and this is clear when you use a sat-nav with this type of traffic updates. In some cases, the warnings can be excellent, letting you know about a severe jam which has brought a major motorway to a standstill, and allowing your sat-nav device to suggest an alternative route. Unfortunately, though, a lot of the time you will find yourself sitting amongst a stationary column of vehicles which hasn't been detected at all. So time can be saved on occasion if you're a frequent traveller, but RDS-TMC is far from infallible.
All of which brings us to TomTom's HD Traffic. This uses a different way of collecting traffic information and a different method for delivering it to the device. Instead of cameras and designated fleet vehicles, mobile phones and compatible TomTom devices provide the raw information. In the UK, the mobile phone network partner is Vodafone, which has 16.7 million customers at the last count. In order to direct call data, all mobile phone systems know which cell towers their users' handsets are closest to. But locations can be calculated with greater accuracy by triangulating between towers. You may have seen this technology used to track criminals in American cop shows, but it's not fiction at all. Google Latitude and Apple's non-GPS iPhones also employ this capability.
So HD Traffic keeps tabs on mobile phones as they travel down roads, and uses this information to calculate the average road speed in a similar fashion to RDS-TMC's Trafficmaster cameras and fleet vehicles; except that in this case the sample size is significantly larger. This means that the information is potentially much more accurate, and likely to cover most UK roads. HD Traffic also receives information from Trafficmaster, to further improve accuracy. Even if you're not a TomTom owner, you can see the results for yourself on TomTom's website. Updates are delivered to TomTom LIVE devices every three minutes via a built-in mobile data link, so more frequently than RDS-TMC and less susceptible to temporary coverage blackouts.
HD Traffic sounds brilliant on paper, and we were bowled over when we first tested it. We're glad to say that we still think it's the most reliable traffic system yet, so we can continue to stand behind the positive review we gave the GO 540 LIVE. However, like any technology, you need to know how to use HD Traffic to get the best results. It may be the best traffic system we've seen so far, but it does have a few limitations.