I didn't find this glitch. It was me and my friend. You may already know this but we found this ourself so if this is brand new I take credit for it. If people already know this then

Tutorial:

1. Go to T-Bone Junction (Need Secret Armory DLC)

2. Get a vehicle from catch-a-ride (With scooter man!) Preferably the racer.

3. Go left from the catch a ride (The part of T-Bone Junction where it stops with like a half curved circle sought of shape if you know what I mean.) and there should be a small gap in the fence/raillings

4. Drive your vehicle off the side on that point (Go slow entering it, then go faster)

5. When your vehicle is about to fall off the edge, press (Y) to switch seats. This disable's the death barrier.

6. Once your on the floor, press (Y) to change back into the driver's seat. You can NOT get out once your in the vehicle, only later on.

7. Keep on driving away from T-Bone Junction until the red death screen disappears.

8. When it goes normal, you can now get out of your vehicle and explore the MASSIVE world of under and out of T-Bone Junction.

I would really appreciate rep if I am the finder. I'm not asking for rep, i'm just hinting at it.

Maybe found by - Cameronza

GamerTag - Cameronza

If you want any help doing this glitch, i'm proud to create a lobby for a few hours every day between 7-10pm GMT (UK)