How to make the model moving with CFrames in the best way?

seat = script.Parent
tram = script.Parent.Parent.Parent
local plr = game.Players.LocalPlayer

while wait() do
    if seat.Occupant == nil then
        --print("sitting")
        seat.Occupant.Parent.isDriving.Value = true
        --print (tram.Body.forward.Value)
        while tram.Body.forward.Value == true do
            --Here is script which moves the train but this one doesnt work
            -- Ah, and "we have scripted things like pressing w etc"
            script.Parent.Parent.CFrame = CFrame.new(script.Parent.Parent.CFrame + Vector3.new(0,0,1))
            wait()
        end

        while tram.backward.Value == true do
            wait()
        end
    end
    wait()
end

How to fix that CFrame moving script, is there any good way (it need to be moved with players of course)?