Standing vehicle on slip road to M18

A driver of a vehicle was stationary on the slip exit to the M18 from the m180, thinking the traffic lights (on red) intended for the M18/m180 and moto Doncaster services junction. I waved frantically at the driver, as I waited correctly at the traffic lights, to indicate they needed to keep moving on. They were lucky no big HGV was coming up behind them. This is not the first time I have witnessed someone sat on the slip exit thinking the red light was for them!!...this is an accident waiting 😕, my suggestion, it needs a shield to obscure the light on the left.