Opening the left side cab window causes the train brakes to enable and stops you from going any faster or moving at all if stationary.
Hi HopesAnchor131 have you got the Droplight Interlock, cut out? As this will not allow the train to move as this is a real safety feature on the Tube Stock.
The Droplight Interlock is a safety feature from what I understand. If you were to stick your head out the window, you would instantly meet tunnel wall.