Minecraft Tutorial SE01 - Safety Bridge

A Bridge of safety is one that prevents you from falling and has its cost reduced to the lowest.
The way it works is that the player is 2 blocks tall, and it will block the player's head so that there is no way to fall down from your current position.

It can also be used with lava, or other dangers.
It is really useful and the cost isn't much.

Hope that this helped you!