It's just a T crossing walkway but without a gap in the railing that can be walked through. You can still crouchslide under the railing. It is unlocked automatically when you unlock the vanilla walkways in the AWESOME shop.
The SafeT walkway (center), alongside a vanilla T walkway (left) and a straight walkway (right) for comparison. Yes the vanilla straight walkway and the SafeT walkway are squished lengthwise, thats just how the vanilla asset is.
Model and texture assets 'ethically recycled'™ from the Coffee Stain Studios' dumpsters