Hey, im making a Train currently and wanted to know how to make a Sound louder.

Lets say this is the Speed:

0 Kmh --------40 Kmh-------- 80 Kmh

0 Volume ----------5 Volume----------10 Volume

And this over me is the Volume: /\

How could i archieve that if the Speed is 40 Kmh that the Volume is 5 and if the Speed is at 60 Kmh the Volume is at 7.5.
I could do that with many if statements but can i do another way? I dont know what Magnitute Vecolity is (I thing how fast the Vehicle is going) could it work with that?
Thanks!

Thanks to u both i will try it out now and i use VectorForce to move the Train how can i know how fast is 100 Z or X Force, i mean how could i know how much kmh is 1000 Z or X Force?
Thanks!