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made it much much worse
This. Previously rat runs will have been local knowledge, and if you were out of your area then you would be reliant on signposting and a map to get where you wanted to be, which would largely make staying on signposted main roads the most convenient means of navigation. Unless you had a highly adept map reader in the car to navigate you. Which is exactly what everyone now has.
In terms of rat-running I do wonder what difference google maps, Waze, etc has made to it.
I tend to stick google maps on even when I'm driving routes I know just to keep an eye out for traffic and because I'm already using the phone for music.
The majority of the time I'll get it directing me off an A road to a B road to avoid traffic (routes are almost identical length or the diversion can be longer). For those who know it the most obvious one is that you get directed off Green Lanes/Seven Sisters onto Wightman Road/Tollington Park almost every journey. You can see that a lot of traffic is also following the same diversion as people will all turn at the same points, etc