According to Hanafi Fiqh, it is not lawful to offer Zuhr and Asar salah together or Maghrib and Isha salah together during travel. However, you may combine them in a way that you offer Zuhr salah in its last time and the Asar in its first time, then it is correct. Likewise, offer the Maghrib in its last time and Isha in its first time, then it shall also be lawful. It is not lawful to combine them in a way that Salah is performed before its time. If the bus driver does not accept it then you will have to make the qaza of one of them and the bus driver shall be responsible for the same.
Allah knows Best!
Darul Uloom Deoband