No sat nav is 100% reliable 100% of the time.

Google Maps once asked me to leave motorway citing it is closed - in reality I continued as it just normal.

At times it opted for narrow country lanes instead of slightly longer but A roads. I have noticed that it tends to adopt a route which is shortest time even by a small margin. So in a 2 hour journey, if motorway route takes 2:01 hr and a non motorway highly convoluted road takes 1:59 hr it will go for convoluted route.

My built in car navigation (though now out of date) always give option for [1] shortest by distance [2] fastest by time [3] most fuel economic routes. I tend to choose [2] most of the time.

Often what works well in one area or for a route doesn't work so well for others - or other types of travel.

A local cycling route to me in Herts on country roads (all public) never works on Google Maps, trying to divert me around a bend in the road in one village, yet is perfectly fine if I change the travel method to 'car'. No reason why this is, and seemingly no idea how to get Google to change the routing software to fix the error.

I don't know if all the satnav providers share their user data - not personal details, but how users faired when actually going certain routes vs the estimated speed / traffic levels. If locals don't use satnavs and few users of a particular provide use the road, then the data held may not be that accurate to give a representative idea of what the journey will be like.

This would be of far more importance when a stanav wants to take you down country lanes, especially narrow ones but which are 'de-resticted', when in reality you have to go much slower and can, in some circumstances be quite dangerous in comparison to longer, easier-to-drive routes on more major roads. Particularly if the 'time save' (at the best of times) is minimal.

I also still find that Google Maps (not sure about the competition) can be out of date on traffic jams / significant incidents by easily 30 mins, often much more. I wonder how much the providers generally rely on just data from people's cars / phone apps etc and how much from the Highways people, given their dot matrix signs are often well out of date by similar amounts.

At times it opted for narrow country lanes instead of slightly longer but A roads. I have noticed that it tends to adopt a route which is shortest time even by a small margin. So in a 2 hour journey, if motorway route takes 2:01 hr and a non motorway highly convoluted road takes 1:59 hr it will go for convoluted route.

It did that for me last weekend.

We were away in our caravan. Left the 'van on site and dropped Mrs B at RHS Wisley and took my self of to see the planes etc at Brooklands.

Returning to Wisley it took me along lanes and around Wisley village including very narrow bridge by Pyrford Lock. OK in the car but while I know the 'van (generally) follows the car and is only a few inches wider I'd have been well anxious going through the width restriction at the end of a left curve:

goo.gl/maps/2h2HvQQwzjRe6rF79