This will help if your annoyed by always having to go back because the yellow dude locks the door. First find a warthhog and get some people inside. Go where the place where there are lots of guys and where kortana says the covenant are putting up a real fight. Go down completely with your warthhog and go at full speed directly where the yellow dude is. If you did it right then your warthhog will be half way through. Press forward and get out. Then pass the level like you usually do and come back where the warthog is stuck. You may think it is impossible to get out but just press back and then get out. You will be in back of it and now you're done the hard part!