Volvo says magnets have great potential for autonomous vehicles since established positioning technologies like GPS and cameras have limitations in certain conditions. Road-integrated magnets remain unaffected by physical obstacles and poor weather conditions. Just don't drop your credit card.
Sweden is working hard to be the world leader in autonomous technologies. They have been experimenting with road trains for a while and will have a fleet of a hundred self-driving cars on the streets of Gothenburg in less than three years.
Meanwhile, Volvo Cars and the Swedish Transport Administration also built a 328 foot long test track just outside the city full of round ferrite magnets (40x15 mm) located eight inches below the road surface. The idea is that with the cars being equipped with several magnetic field sensors, the magnet-based positioning will prevent run-off road accidents, any damage to snow-covered objects such as barriers and signs and offer better accuracy overall than a GPS or camera-based system.
The government side also wants to evaluate crucial issues such as detection range, reliability, durability, cost and mostly the impact on road maintenance, but so far they say that "ferrite magnets are an efficient, reliable and relatively cheap solution, both when it comes to the infrastructure and on-board sensor technology".
I imagine it to be something like this: