25-05-2008, 03:31 AM
KrishJ Wrote:While calculating the headway for a particular layout, we need the following inputs such as Line Speed, Dwell time (However N/A for Non-stopping trains), Platform Length, Train Length, Overlap distance for calculating CP, Acceleration, Service Brake, Emergency Brake, Drivers reaction time for placing the Sighting Points and with some assumptions. From this we can calculate the Headway in seconds.
Also if we know the Headway timing we can achieve by adjusting the signal positioning or introducing intermediate signals we can meet.
Indeed- this is why it is important to declare practices and state assumptions. In the UK it is generally true that the overlap provided for "Mainline" is not directly based on emergency braking, whereas on "Metro" it is.
Another significant difference is that "Metro" signal positioning is primarily dictated by headway considerations and trains stopping in platforms, whereas signal spacing to ensure adequate service braking from first warning to stop signal is particularly important for "Mainline"- the signal spacing arranged due to braking gives implications for headway. Must go now- using free internet at departure gate in Singapore airport and approaching flight time!
PJW