Is it permissible for a traveler to combine the Asr prayer with the Dhuhr prayer if his prayer begins before his journey, knowing the distance of travel and the arrival times? And if permissible, should Dhuhr be prayed four rak'ahs and Asr two rak'ahs?

If you intend to combine and shorten prayers, you are not permitted to do so until you have embarked on your journey and passed beyond the houses of your town, based on the Almighty’s saying: "And when you travel throughout the land, there is no blame upon you for shortening the prayer." It is preferable for you to do what is easier for you, whether it is offering the combined prayers earlier or delaying them.