 The holding of the train for one minute after the green aspect was reasonable, but the driver should have been instructed to, "... proceed at caution and be prepared to stop short of any obstruction".The absence of the last instruction meant that the driver would proceed at full speed and be unable to stop short of another train.As a result, the berth circuit (not to be confused with the berth track circuit) was developed whose purpose was to detect contacts that were closed when they shouldn't have been and to rupture the relay supply fuse if such a condition was detected forcing the controlled signals to show an unchanging danger indication.