Something like this:
"Oncoming riders, welcome to Steel Venom. Please step into your car, pull down your harness and wait for an attendant. Leave any loose articles behind. Riders on the platform, take a step away from the gates in front of you. The gates are now closing. Keep your hands and arms in the car at all times and enjoy the ride."
This next part started as:
"All right, we're ready to rock. Steel Venom's gonna strike in 3, 2, 1!"
And eventually morphed into:
"Launching in 3, 2, 1!"