If you weigh 250-400 kilo that is quite a bit, add in 40-50 kilo for the cart plus the junk hanging off of it and that is in the range of the lowest weight cars that exist today. But the tires from these things are a lot smaller, meaning more pressure on a smaller area. I think that is the magic trick. You could probably drive a truck over these sensors, provided the pressure per cm2 is low enough, if they are pressure based. If not, a small radar sensor does not care about weight. They likely would install such sensors if enough people come in in beetusmobiles.