American Audio VELOCITY - REV 4-05 Betriebsanleitung PDF herunterladen (Seite 60)

METRO RAIL DESIGN CRITERIA SECTION 9 / SYSTEMS

DE304.09 9-55 Revision 4 : 05/09/12

Metro Baseline Re-Baseline: 04/29/10

interlocking conditions, civil speed limits, and grade crossings.

The cab signal system shall impose speed restrictions due to civil/track speed limits. In the

normal direction of traffic the following design requirements shall be followed:

 The speed code reduction shall occur at a point no further than 110% of the Civil

Braking Distance from the point of restriction.

 The cab signal and block design shall enable acceleration to the authorized speed

(within safe braking constraints) to commence within 400 feet of the end of the

speed restriction area.

 The maximum block length shall be 5,000 feet.

 All track circuits with a Maximum Authorized speed (MAS) exceeding 35 mph shall

have at least one intermediate speed code before “STOP”.

 Exceptions to the above criteria shall be reviewed on a case-by-case basis.

The cab signal system shall impose speed restrictions on the approach to stations with an

at-grade crossing on the exit side of the station. In the normal direction of traffic the

following design requirements shall be followed:

 Speed code reduction, or removal of cab code shall occur on the approach to, or the

exit from, the station to ensure that a train that fails to make a station stop, or does

not make a full 20-second dwell, cannot enter the crossing unless the entrance

gates are fully down.

 Speed code reduction, or removal of cab code shall, never–the-less, maximize the

train speed into the station.

 Speed code reductions shall be calculated using the Civil Braking Distance formula.

 Speed code reductions shall occur at a point no further than 120% of the Civil

Braking Distance from the near side of the crossing.

 Crossings shall be activated automatically, assuming a 20-second station dwell.

Once the entrance gates are down, full speed cab code shall be available.

 Where the crossing is within 100 feet of the station, a TWC system shall be provided

to enable crossing calls to be called or cancelled.

9.4.3.2 Safe Braking Distance Model

9.4.3.2.1 Introduction

The Safe Braking Distance (SBD) is the calculated distance that a worst-case train will

travel between the time that a speed reduction is commanded until the required speed

reduction is achieved. The train operator is in control of the speed with the cab signal

system providing over-speed protection only. The design shall utilize the SBD formula for all

safety braking requirements.

The Civil Braking Distance (CBD) is the calculated distance that a train will travel between

the time that a civil speed reduction is commanded until the required speed reduction is

achieved. The train operator is in control of the speed with the cab signal system providing

over-speed protection only. The CBD formula shall not be applied to safe train separation.

Initial Entry Speed

For SBD and CBD calculations, an initial entry speed (S) is used, which is derived from a

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American Audio VELOCITY - REV 4-05 Betriebsanleitung Seite 60

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