The force of a 60 mph crash is twice as great as a 30 mph crash?

No, it is 4 times as great. Looking at the equation for kinetic energy: E=0.5 x m x v x v

Where E=kinetic energy

m = mass of vehicle

v = velocity of vehicle

If the vehicle weighs 1000 kg and is traveling at 10 m/s the kinetic energy possessed will be 1000 x 10 x 10 = 100,000 joules

Whereas if the same vehicle is traveling at 20 m/s it would be 1000 x 20 x 20 = 400,000 joules. In other Words, the vehicle possesses four times as much energy.