It's a trap. Obviously what makes this level harder than pretty much any of the other levels is because of the driving/uv ray portion. The trick to this part of level is to stop at the kryll parts and allow your gunner to kill them while the kryll are in front. There are not an infinite amount of kryll, if you kill all the one in area they dont come back as far as i know. If you can get to the non freeway section with over 75% life left, its actually very achievable you can kind of ease up on the latter half. Just run and uv gun the latter half with your gunner just hitting the biggest waves of kyrll ignoring the one or two nuisances and you should just make it to the end.
Also, there is a semi glitch where by you can still pass this part with dying, if you make it to end. Ie after the jump, the guy says something, you can luck out and still get the clear, btw this also happens in other parts of the game (dying but passing to the next part due to a cut scene).
Lastly, in general tell your gunner, not to shot the ray needlessly. There are times when a kryll or two fly around, but unless you see your bar going down leave them be. Your gunner can waste time, as when he shots you don't drive.
One final general note, on areas where you spilt up the key it to work as a team. Although you spilt up the paths either directly or indirectly connect. And often tough enemies on your path can be taken out by your partner with minimal effort and vice versa. If you are really a terrible player and just riding someone's coat tails, then just hang back, and in most areas your partner can clear out your and his area.