6.4 Lane change states diagonal movement not allowed, I dont see what the difference is by moving forwards then sideways, seems to be overcomplicating the rule, I did wonder about successive sideways movement though and wondered whether alternating with forward movement would be more realistic
I think it is suppose to simulate the difficulty of moving to the left or the right with a team of horses and a chariot. If you want to change lanes it is one space forward and then one space to the left or right. If another chariot is directly in front of you when you start your movement you must use a different kind of move as you are unable to move the one space front before changing lanes. I forget what the movement name is it could be sideslip or something like that but it costs you three movement I believe to move one space to the left or right when you are blocked like that.
It would be pretty unrealistic to move from the 1st lane all the way out to the 8th lane without ever moving forward. Chariots just don't move like that.