Naylor Road Metro Station Area Access and Capacity - WMATA.com.

Time to Reach a Point of Safety
Calculating the time to reach a point of safety (defined as the street level completely outside of
all station structures) employs the same principle. After clearing the platform, the capacity of
faregates (assumed to be open in an emergency) and the width of the mezzanine exit may be
limiting factors in how quickly the station occupant load reaches a point of safety. In addition
to the time spent walking along the exit path, the analysis accounts for the wait time at each
potential choke point along the way. The analysis found that wait times at faregates and
mezzanine exit would be non-existent, as the person-per-minute throughput capacity at each
potential chokepoint increases as the passengers get closer toward the exit. In other words, the
platform-to-mezzanine stairways and escalator are the only bottleneck in the station. Passenger
queues would form on the platform in an emergency situation because of the limited throughput
capacity of the stairways and escalator. These vertical circulation facilities would act as a funnel,
allowing only some of the passengers through. The comparatively larger throughput capacity
of the faregates and the mezzanine exit ensures that the limited number of passengers that have
already descended to the mezzanine can proceed without waiting in additional queues.
Table A-15 details the analysis inputs used to calculate times to clear the station platform and to
reach a point of safety.
Table A-16 summarizes the vertical, faregate, and mezzanine exit capacity, as well as the walking
time for the longest practical route to reach a point of safety under 2012 and 2040 ridership.
Tables A-17 and A-24 provide a detailed breakdown of the NFPA 130 morning and afternoon
peak analyses.
Table A-15: NFPA 130 Analysis Input Data
Category Value Units Source
Metrorail crush capacity 220 Passengers/car Metro Manual of Design Criteria for Maintaining and Continued Operation
of Facilities
Escalator width 48 Inches Metro Manual of Design Criteria for Maintaining and Continued Operation
of Facilities
Stair width 60 Inches Metro Manual of Design Criteria for Maintaining and Continued Operation
of Facilities
Surge factor 1.3 Metro Ballston-MU Station Exiting
Walking speed 124 Feet/minute NFPA 130: Standard for Fixed Guideway Transit and Passenger Rail Systems
Vertical walking speed (down) 48 Feet/minute NFPA 130: Standard for Fixed Guideway Transit and Passenger Rail Systems
Capacity for stairs and stopped 1.41 Persons/inch/minute NFPA 130: Standard for Fixed Guideway Transit and Passenger Rail Systems
escalators (down)
Capacity for faregates 50 Persons/minute NFPA 130: Standard for Fixed Guideway Transit and Passenger Rail Systems
Capacity for ADA or emergency
faregates
75 Persons/minute NFPA 130: Standard for Fixed Guideway Transit and Passenger Rail Systems
87 | Appendices