Headway Calculation and Signalling braking Distance for Railway Signal Placement

Headway Calculation and Signalling braking Distance for Railway Signal Placement

Headway Calculation and Signalling braking Distance for Railway Signal Placement Network Rail

Headway Calculation and Signalling braking Distance for Railway Signal Placement

HEADWAY FOR NON-STOPPING TRAINS

* HEADWAY CALCULATION IS THE NECESSARY FIRST STEP IN SIGNALLING A LAYOUT

It provide best engineering solution , which meet the conflicting requirements of Operational capacity, Safety & cost.

* HEADWAY IS A MEASURE OF HOW FREQUENTLY TRAINS CAN RUN.

IT IS RECKONED (established by calculation) IN THE FORM OF

(i) HEADWAY TIME OR (ii) HEADWAY DISTANCE

* ‘HEADWAY TIME’ (HT) IS THE TIME TAKEN BY THE FOLLOWING TRAIN TO PASS PAST A GIVEN POINT ON TRACK AT FULL SPEED AFTER THE PREVIOUS TRAIN HAS PASSED IT, SUBJECT TO THE MINIMUM SEPARATION PERMITTED BY THE SIGNALLING SYSTEM.

* ‘HEADWAY DISTANCE’ (HD) IS THE DISTANCE BETWEEN TWO SUCCESSIVE TRAINS PASSING THE SAME POINT WITH THE FOLLOWING TRAIN AT FULL SPEED, SUBJECT TO THE MAXIMUM FREQUENCY PERMITTED BY THE SIGNALLING SYSTEM.

CALCULATION OF HEADWAY DISTANCE

uTHE PURPOSE OF HEADWAY CALCULATION IS TO DETERMINE WHAT TYPE OF SIGNALLING, WITH WHAT SIGNAL SEPARATION, IS REQUIRED TO MEET THE CUSTOMER’S SPECIFICATION IN THE MOST COST-EFFECTIVE MANNER.

HEADWAY CALCULATION

SUMMARY OF THE CALCULATION PROCESS IS :

1.DECIDE THE MOST INTENSIVE TRAIN SERVICE WHICH DICTATES THE ‘HEADWAY CALCULATION’ FOR EACH LINE.

2.CALCULATE THE ‘SERVICE SPEED’ IN m/sec

3.CALCULATE THE HEADWAY DISTANCE’(HD) FOR THE LINE (HT x V)

4.CALCULATE ‘DISTANCE FROM GREEN TO RED’ (DGR = HD-R-O-L WHERE ‘R’ IS THE SIGNAL READING DISTANCE’, ‘O’ IS SIGNAL OVERLAP & ‘L’ IS THE MAXIMUM TRAIN LENGTH)

5.CALCULATE THE RATIO OF ‘DISTANCE FROM GREEN TO RED’ TO THE SIGNAL BRAKING DISTANCE (N = DGR / SBD)

BASED ON THIS CALCULATION OF ‘N’ AND A POSSIBLE ‘SIGNAL SEPARATION RANGE’, SELECT THE TYPE OF SIGNALLING SYSTEM TO BE PROVIDED.

SPACE BETWEEN SUCCESSIVE STOP SIGNALS

* REQUIRED SPACE BETWEEN SUCCESSIVE STOP SIGNALS ‘D’ IS GIVEN –

AS ‘D2’ IN 2 ASPECT SIGNAL TERRITORIES,

                    AS ‘D3’ IN 3 ASPECT SIGNAL TERRITORIES &

                    AS ‘D4’ IN 4 ASPECT SIGNAL TERRITORIES.

* THE PARAMETERS CONSIDERED FOR CALCULATING THE SIGNAL SPACING ARE:

(1) HEADWAY TIME IN SECONDS (HT), (2) HEADWAY DISTANCE IN METERS

(3) TRAIN SERVICE SPEED (V) IN METERS PER SECOND (m/s) TO BE CONVERTED FROM MILES PER HOUR (M/H) AS GIVEN.

* REQUIRED SPACE BETWEEN SIGNALS IS CALCULATED BY FORMULA: D = V * HT (SPEED x TIME) MAXIMUM SPEED AND HEADWAY TIME, BOTH ARE SPECIFIED BY THE CLIENT AS REQUIRED.

SIGNALLING BRAKING DISTANCE

* ALSO CALLED ‘SERVICE BRAKING DISTANCE’(SBD), THIS IS THE MINIMUM PERMITTED

DISTANCE ON THE APPROACH TO A ‘RED’ ASPECT FROM THE FIRST RELEVANT ‘CAUTION’

ASPECT (‘YELLOW’ OR ‘DOUBLE YELLOW’ IF USED).

* ‘SBD’ IS DEPENDENT ON:

(1)THE MIX OF TRAIN TYPES USING THE LINE (AS SPECIFIED BY THE CUSTOMER)

Different train have different train braking capability ( worse to be consider )

(1)THE MAXIMUM PERMITTED SPEED (ALSO SPECIFIED BY THE CUSTOMER)

(2)THE RULING GRADIENT OF SECTION TRAVERSED (AS MEASURED OR CUSTOMER SPECIFIED)

‘SBD’ IS GIVEN IN A LOOK UP TABLE WITHIN RAILWAY GROUP STANDARDS FOR REFERANCE

 

SIGNALLING BRAKING DISTANCE (Manual calculation)

SIGNALLING BRAKING DISTANCE

CALCULATED SIGNAL BRAKING DISTANCE

* THIS DEPENDS ON THE TRAIN BRAKING CAPACITY, ‘a’ IN UNITS OF:   ‘m per Sec per Sec’(m/s2).

ITS TYPICAL VALUE = 0.5 m/s2

SBD, S = U2/2a, WHERE ‘U’ IS THE MAXIMUM TRAIN SPEED & ‘a’, THE TRAIN BRAKING CAPACITY.

(Signal Braking Distance (S) is directly proportional to the required maximum train speed and inversely  proportional to the available train braking capacity both given by the client).

* TO CALCULATE ‘SBD’ FOR 100 MPH TRAIN SPEED:

(a) first, convert speed units from MPH to ‘m/s’.  100MPH = 100 x (1609/3600) = 44.7 m/s.

(b) then, S = (44.7)2 /2a = (44.7)2 / 2 x 0.5 = 1998m.

 

CALCULATED SIGNAL BRAKING DISTANCE

BRAKING DISTANCE using LOOK UP TABLE    Average Gradient

Average Gradient

 

 

Average Gradient2

 

Average Gradient1

SBD (MIN) AS REFERRED IN LOOK UP TABLE

SBD

* ‘SBD’ IS ALSO CALCULATED FROM THE AVAILABLE DATA INCLUDING THE ‘TRAIN BRAKING CAPABILITY’ TO DECIDE THE MAXIMUM SPACE THAT CAN BE CONSIDERED TO BE KEPT BETWEEN THE ‘FIRST CAUTION’ AND ‘RED’ ASPECT SIGNALS TO BE FACED IN SUCCESSION.

 

SIGHTING DISTANCE AND READING DISTANCE

*  ‘SIGHTING DISTANCE’ IS SOMETIMES REFERRED AS THE DISTANCE BETWEEN THE EARLIEST POINT ON APPROACH AT WHICH THE SIGNAL IS SIGHTED FIRST AND THE SIGNAL.

* BUT AT MOST OF THE TIMES, IT IS TAKEN AS ‘THE LAST PERIOD OF UNINTERRUPTED VISION’ ON FINAL APPROACH TO THE SIGNAL, WHICH SEEMS MORE ACCURATE.

* ‘READING DISTANCE’ IS RECOGNIZED WITHOUT THIS AMBIGUITY AS THE LATTER DEFINED SIGHTING DISTANCE WHICH IS CONTINUOUS FOR A STIPULATED PERIOD.

* GROUP STANDARD GE/RT8037 REQUIRES THAT ‘EVERY SIGNAL APPOACHED AT SPEED IS VISIBLE UNINTERRUPTED FOR AN ABSOLUTE MINIMUM OF 8 SECONDS ON THE FINAL APPROACH TO THE SIGNAL, FOR A TRAIN AT MAXIMUM PERMITTED SPEED’

* THIS FINAL CONTINUOUS MINIMUM VISIBILITY ENSURES THAT THE DRIVER IS ABLE TO REACT TO A LESS PERMISSIVE / MORE RESTRICTIVE ASPECT OBSERVED BY APPLYING BRAKES WITHOUT LOSING MUCH TIME (REACTION DISTANCE INCLUDED).

* A SIGNAL MAY BE VISIBLE FROM A LONG DISTANCE ON THE APPROACH. BRAKING (EVEN FOR A WORST CASE TRAIN) ONLY NEEDS TO START AT THE POST OF FIRST ‘CAUTION’ SIGNAL.

 

READING DISTANCE CONSIDERED IN PRACTICE

* IF A TRAIN IS RUNNING TO THE LINE CAPACITY LIMIT, AN INITIAL CAUTION SIGNAL ASPECT MAY BE OBSERVED TO ‘STEP UP’ TO GREEN DUE TO THE EARLIR TRAIN CLEARING ITS SECTION AND MOVING AHEAD BEFORE THE MINIMUM 8 SECONDS HAVE LAPSED.

* A MORE PRACTICAL DEFINITION OF READING DISTANCE, A MINIMUM OF 10 SECONDS READING TIME IS CONSIDERED JUSTIFIABLE IN PRACTICE FOR HEADWAY CALCULATION.

* AS SIGNALS ARE PROVIDED WITH ‘AWS’, THE READING DISTANCE MAY ALSO BE SUCH AS TO FACILITATE THE STEP UP OF SIGNAL ASPECT TO GREEN BEFORE THE TRAIN COMING OVER THE AWS TRACK MAGNET, FOR THE DRIVER TO HEAR ‘SIGNAL GREEN’ WARNING BELL.

* A READING DISTANCE OF 300m IS PRACTICALLY CONSIDERED FOR HEADWAY CALCULATIONS AS IT IS CONSIDERED REALISTIC FOR A SPEED RANGE OF ABOUT 70 MPH (113 kmph).

 

2 thoughts on “Headway Calculation and Signalling braking Distance for Railway Signal Placement

  1. Excelllent article. Keep writing such kind of info on your site.
    Im really impressed by your blog.
    Hi there, You have dopne an excellent job.I will definitely digg
    it and individually recommend to myy friends. I’m sure they’ll be benefited frtom this website.

  2. I am not sure where you’re getting your information, however good topic.
    I must spend a while studying more or figuring out more. Thanks for excellent info I was looking
    for this info for my mission.
    +905443535397

Leave a Reply

Your email address will not be published. Required fields are marked *