American Audio VELOCITY - REV 4-05 Operations Instructions download pdf (Page 61)

METRO RAIL DESIGN CRITERIA SECTION 9 / SYSTEMS

DE304.09 9-56 Revision 4 : 05/09/12

Metro Baseline Re-Baseline: 04/29/10

combination of Cab Signal Speed (CSS), Cab Signal Tolerance (CST), Cab Signal

Overspeed Allowance (CSO), and the Acceleration Allowance (AA) as follows:

CSS = 55, 45, 35, 25, 20, 10, or 0 mph according to the cab signal code immediately prior

to entry.

CST = Tolerance in speed detection, which shall be as follows:

CSS 55 45 35 25 15 10 0

CST

+0,

-1.5

+0,

-1.5

+0,

-1

+0,

-1

+0,

-1

+0,

-1

+1,

-1

CSO = Allowable exceedance of cab signal speed as detected by the carborne cab signal

system, which shall be as follows:

CSS

CSO

2.5

AA = An allowance to account for instantaneous acceleration of the vehicle for the time

delay between the decoding of the speed code by the carborne equipment, and removal of

propulsion power. The allowance shall also include for jerk-limited removal of power and

application of braking.

For SBD calculations, S = CSS + CST + CSO + AA

For CBD calculations, S = CSS + CST + CSO

9.4.3.2.3 Safe Braking Distance Calculation

SBD = D

+ D

, where:

= Reaction distance in feet = S x R x 1.467

= Braking Distance in feet = 0.733 x S

/ (B  0.2G)

= Overhang distance of two vehicles = 30 feet

S = Initial entry speed (mph) prior to braking.

R = Reaction time in seconds (includes operator, cab signal delays and brake build-up) =

9.8 seconds for a change in speed code and 7.2 seconds for code-to-no code.

B = Safe Braking rate = 2.0 mphps

G = Alignment grade as a decimal fraction

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American Audio VELOCITY - REV 4-05 Operations Instructions Page 61

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