How do I respawn a model without removing the original?

I am trying to make the script that Down Hill Smash uses to make cars spawn, and I got it working but the original cars disappear when the new cars spawn, making the cars just disappear.

Any idea's to fix this? (below is code)

model = game.Workspace.Cars.RedCar1 
backup = model:clone() -- backs up the model so it can respawn
while true do 
wait(7) -- regenerates the model after 7 seconds 
model:destroy() 
model = backup:clone() -- loads the backup of the model 
backup = model:clone() -- backs up the model so it can respawn
model.Parent = game.Workspace.Cars 
model:MakeJoints()
end