When we had our first taste of TomTom's HD Traffic system in the GO 540 LIVE at the end of 2008, it was clear that this was one of the most significant developments in sat-nav technology for a good few years. After a six-month run in TomTom's premium GO range, the system is now also being brought to the more budget-conscious XL, of which we will be bringing you a full review shortly. In the interim, we've been testing HD Traffic continually since its release, giving us a much clearer picture of its strengths and weaknesses. This week we bring you our findings.
Before we relate our experiences, however, we should reiterate how HD Traffic works and why it's different from the systems in use up until its release. Traffic updates have been available in sat-nav devices for some years. In order to receive them, your sat-nav needs a special FM radio receiver that can pick up the signals through which the updates are broadcast. The updates are delivered via RDS text. This is the same system that your FM radio uses to display the channel it's tuned into, and is also the source of the automated time reset information available with some car clock-radio head units. The traffic updates are broadcast every 15 minutes on certain FM radio stations. In the UK, this is primarily Classic FM. Clearly, if your signal is poor when an update is broadcast, you will miss it.
But this is only one of the weaknesses of the traditional traffic update system known as RDS-TMC. Road coverage is also far from universal. The UK Trafficmaster system only includes motorways and 95 per cent of trunk roads, so no local routes are tracked. This is due to how RDS-TMC detects jams, and the primary means by which Trafficmaster collects its information are twofold.
First, there are number plate-detecting cameras similar to the ones used by the London Congestion Charge. You may have noticed these devices lurking on UK motorways. By reading the location of specific vehicles on roads, then seeing how long they take to get to the next camera along the route, these cameras can be used to calculate the current average traffic speed on that section of carriageway. If this is well below the limit, there is clearly a jam building up, although the cameras are allegedly never used to prosecute speeders. But where there are no cameras, there will be no traffic information, and it's not cost effective (or desirable for the environment) to have them everywhere.
The other source of information is a collection of 50,000 fleet vehicles with sensors, which automatically report back on their progress along key roads. Clearly, this is a drop in the ocean compared to the 30 million cars in the UK, even if these vehicles do a lot of miles everyday.