guard rail 
noun
1A rail at the edge of something such as a cliff or the deck of a boat that prevents people from falling off: the top bunk has a solid guard rail...
- With the boat beached and the bow tilted up, a guard rail prevented him from taking aim at the enemy.
- It was amazing to see men, women, and children alike chasing the moving bus, hopping on to the steps, then pulling themselves into the vehicle by using the guard rail or the door as a level of sorts.
- If not, consider putting up a guard rail or steel posts to reduce this risk.
1.1 North American term for crash barrier.The vehicle skidded and collided with the interstate guard rail....
- Above us, the guard rail of the elevated east-bound lane was shredded, making it look like the Lincoln had torn through it and nose-dived into the bus.
- The driver lost control under icy road conditions, the van hit the guard rail and flipped over.