Recently Alex C stated "The EMU times are constrained by the delayed clearing of signals at level crossings which leads to preceding yellows and associated 40kph limit and the TSRs for sighting at level and ped crossings."
Since them I have done some calculations to see what speeds trains could pass a yellow signal and still pull up at a red; I have done this for varying proportions of full service braking.
|v^2 = 2.a.s|
|4000 class service braking =||1.1||m/S/S|
|Distance||% braking||v m/S||V kph|
As should be apparent from the table above restricting the speed to 40 kph past a yellow is totally unnecessary in all but a few circumstances where signals are very closely spaced, ARS and the down side of Showground come to mind. In most cases the distance between sticks is 400-500 metres which for moderate braking 50% of full service allows passing speeds over 75 kph.
This is the reason why I advocate each signal having its own "passing at yellow" speed as indicated by a circular yellow plate with the speed marked on it.
The calculations are based on the usual formula for speed, acceleration and distance.