I visit family in Germany every couple of years roughly. It's mind numbing driving in Australia upon return each time. I literally am so bored doing 100, that I start day dreaming and just zone out. Not paying attention at all.
Switch to Germany, you're driving faster, you're more focused, you are alert and driving better. Then, jump on the Autobahns and you're REALLY focused, driving better than you ever have. Because you have to. They've done the studies, the faster you drive, the more you concentrate. It's just what it is.
So yeah, each time I return home, I feel it's more dangerous driving here.