I've almost finished planning a ride from Munich to Tehran via the Eurovelo 6 route through Austria, Slovakia, Hungary, and Northern Serbia. I want to leave the Danube in Belgrade and continue south via Niš to Sophia and Plovdiv towards Istanbul. Can anyone recommend the safest roads for cyclists on this route? Are the regional highways in Serbia (designated by an R and a number) safe to cycle on? We will be leaving Munich in late August... dates are not set yet, as my travel partner hasn't booked his flight from Australia to Europe yet. Any advice for the route would be very welcome!