Tomb Raider I-III Remastered Starring Lara Croft

I'll leave the glitchless solution up for reference, but it might be way easier to take the easy way out via this skip and then reload save to get the rest of the items/secrets while being able to shoot these annoying blokes:

NEVADA Desert - you only have to deal with dam workers (the guys who look like they belong in some kind of biker gang) twice. The first 2 are easily ignored, while the other bunch requires some prep as you have to drive the quad near them and you only get one shot at getting it onto the roof without one of them throwing himself into the quad killing himself in the progress.
Before jumping over the electrical fence, make a save in case you're too slow.
Once you're inside make a run for the quad and drive it onto the roof with the keycard. Leave it there for now, go into the building underneath you, turn off the fence and open the gate afterwards. Then jump back onto the roof via the block and drive the quad past these guys and onto the next level.