Sat navs: why they don’t tell the truth and how to get the best from one

Sat navs

“Take the next left. Or is that right?” Sat navs aren’t always infallible

Sat navs are one of the wonders of modern motoring ‑ until they direct you to somewhere you don’t want to be. There are numerous stories of satellite navigation systems going bad. Drivers have been directed onto the middle of ski slopes, articulated lorries pointed down totally unsuitable country lanes and coach parties sent on 750-mile detours.

Although most of us have been led up the metaphorical garden path by a sat nav at one stage, they will become an even more vital part of modern life. From December 2017, drivers will have to follow follow a navigation system for at least part of their driving test.

Research by uSwitch suggests that around four in five of us rely on navigation systems over maps. And more than half (56 per cent) use the navigation unit as a handy reminder of the speed limit.

However, systems aren’t 100 per cent reliable. Research carried out by uSwitch found that around one in five drivers (17 per cent) had been given the wrong speed limit by their navigation system. So why are we being misled by our sat navs? And what can we do about it?

Why don’t sat navs tell the truth?

According to Ordnance Survey, Global Positioning Satellite (GPS) positions are accurate to within five to 10 metres on the ground and 10 to 20 metres in height. However, signals can be distorted through bad reception and obstructions such as trees and tall buildings. A bigger problem is that owners don’t frequently update their nav mapping or software. According to the uSwitch survey, only four in 10 drivers (42 per cent) with sat navs regularly update them.

How up to date is mapping?

A satellite navigation system is only as good as the information it’s fed with. The roads are constantly changing with different traffic priorities, new roads opening and changing speed limits. Ordnance Survey says: “We aim to capture significant change to the landscape within six months of completion to maintain the currency of our national geographic database (NGD).” It claims to have 340,000 miles of network depicting all road carriageways in the UK.

Where does live traffic info come from?

Some navigation systems supply traffic updates. Cheaper units get their information from Trafficmaster’s Traffic Message Channel. This uses the cameras you see on bridges and gantries to measure journey times. The information is free to sat nav providers. Other systems use data harvested from the millions of mobile phones on the move around the country. Thankfully, this is made anonymous before it’s supplied.

How do sat navs work?

As with all computers, sat navs work with hardware and software. The software is partly developed by the sat nav supplier but relies on information from other organisations. For example, map maker Ordnance Survey furnishes the industry with its mapping data though some nav companies get their maps from other sources. Information about traffic jams and road closures comes from the government’s Highways Agency and independent companies such as Inrix. The sat nav uses all this data to formulate the route it suggests you take.

How to update your sat nav

Sat navs

Just as your computer performs automatic updates using the internet so navigation systems need to be updated to display the latest road information. When you’re buying a sat nav it’s worth finding out whether they have lifetime updates for free or whether you have to pay an annual subscription for them. Free maps for the lifetime of the device are becoming increasingly common. The sat nav manufacturer’s website will tell you when updates are available. You then connect the device to your PC and it will perform the update.

Take your time

According to sat nav provider TomTom, our roads change by around 15 per cent per year. It recommends drivers update navigation systems every three months or so. But it’s not the work of a moment. For example, sat nav company Garmin says the map update for Western Europe is 3.5Gb and takes about three hours to download. That obviously depends on your broadband speed, but the message is: if you want to update your maps, don’t leave it until five minutes before departure. Otherwise you could become one of the stories other people read and laugh about.

 

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