If you were an engineer of an actual roller coaster, what information would you need to know to ensure that your coaster would be safe?

To ensure the roller coaster is 100% safe you would have to make sure that the acceleration is a a good force so it can be safe and you have to know how to uses the forces correctly like for example a big change in speed or direction it will make a bigger acceleration and a slower speed or a small change in direction would be a smaller acceleration.