Can't create car movement?

So I was trying to make a car movement script for all devices and this happened: when the player moved left/right while moving forward/backwards it stopped the car completely, the reason why was because the script did not know whether i was moving forwards/backwards or right/left because the direction was in the middle of both of them, now i want to get the horizontal and vertical movement (in numbers). Here's the failed script:

while true do
    wait()
    if script.Parent.Occupant then
        local camera = game.Workspace.CurrentCamera
local humanoid = script.Parent.Occupant -- fill this in with your valid humanoid

if (humanoid.MoveDirection:Dot(script.Parent.CFrame.LookVector) > 0.75) then
    -- we're going right
    print("movefor")
    script.Parent.Velocity = script.Parent.Velocity + script.Parent.CFrame.LookVector * 5
    elseif (humanoid.MoveDirection:Dot(script.Parent.CFrame.LookVector) < -0.75) then
    -- we're going right
    print("movebac")
    script.Parent.Velocity = script.Parent.Velocity + script.Parent.CFrame.LookVector * -5
end
if (humanoid.MoveDirection:Dot(script.Parent.CFrame.RightVector) > 0.75) then
    -- we're going right
    print("turningright")
    script.Parent.Velocity = Vector3.new(0,0,0)
    if script.Parent.RotVelocity ~= script.Parent.CFrame.UpVector * -10 then
    script.Parent.RotVelocity = script.Parent.CFrame.UpVector * -10
    end
    script.Parent.Velocity = script.Parent.Velocity + script.Parent.CFrame.LookVector * 5

elseif (humanoid.MoveDirection:Dot(script.Parent.CFrame.RightVector) < -0.75) then
    -- we're going left
    print("turningleft")
    script.Parent.Velocity = Vector3.new(0,0,0)
    if script.Parent.RotVelocity ~= script.Parent.CFrame.UpVector * 10 then
    script.Parent.RotVelocity = script.Parent.CFrame.UpVector * 10
    end
    script.Parent.Velocity = script.Parent.Velocity + script.Parent.CFrame.LookVector * 5
        else
        script.Parent.RotVelocity = Vector3.new(0,0,0)
end
        script.Parent:SetNetworkOwner(game.Players:GetPlayerFromCharacter(script.Parent.Occupant))
    end
end