on foot (not 20km, usually its something like 3-5km AFAIK, 20km is the width of both sides strongpoints + no-mans-land between), or on some fast and agile one-way craft: motorcycles, buggies, e-bikes

the key idea is that you need something which can get you onto the enemy position either before hunter drones take off, or that a drone won't take out the whole complement, hence the uselessness of trucks

going on foot is not really due to the human wave nature of the attacks, but rather its like WW1 stosstruppen - they use whatever cover they can find and a squad of 4 on foot is much easier to go through bushes used as cover or when weather is not suitable for flying

of note here is that trucks were not really used for transport on the tactical level on the frontline, however lately (with drones from destinus) logistics runs in the rear have also become a problem even 100km+ deep - thats where the 90% killrate figure comes from