Page 215 - Planning and Design of Airports

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from both runways are not allowed in VFR conditions for closely spaced
parallel runways. In IFR conditions, closely spaced parallel runways can-
not be used simultaneously but may be operated as dual-lane runways.
Intermediate parallel runways may be operated with simultane-
ous arrivals in VFR conditions. Intermediate parallel runways may
be operated in IFR conditions with simultaneous departures in a non-
radar environment if the centerline spacing is at least 3500 ft and in a
radar environment if the centerline spacing is at least 2500 ft [5].
Simultaneous arrivals and departures are also permitted if the center-
line spacing is at least 2500 ft if the thresholds of the runways are not
staggered [5]. There are times when it may be desirable to stagger the
thresholds of parallel runways. The staggering may be necessary
because of the shape of the acreage available for runway construc-
tion, or it may be desirable for reducing the taxiing distance of takeoff
and landing aircraft. The reduction in taxiing distance, however, is
based on the premise that one runway is to be used exclusively for
takeoff and the other for landing. In this case the terminal buildings
are located between the runways so that the taxiing distance for
each type of operation (takeoff or landing) is minimized. If the runway
thresholds are staggered, adjustments to the centerline spacing require-
ment are allowed for simultaneous arrivals and departures [5]. If the
arrivals are on the near threshold then the centerline spacing may be
reduced by 100 ft for each 500 ft of threshold stagger down to a mini-
mum centerline separation of 1000 ft for aircraft with wingspans up
to 171 ft and a minimum of 1200 ft for larger wingspan aircraft. If the
arrivals are on the far threshold the centerline spacing must be
increased by 100 ft for each 500 ft of threshold stagger. Simultaneous
arrivals in IFR conditions are not permitted on intermediate parallel
runways but are permitted on far parallel runways with centerline
spacings of at least 4300 ft [5].
The hourly capacity of a pair of parallel runways in VFR condi-
tions varies greatly from 60 to 200 operations per hour depending on
the aircraft mix and the manner in which arrivals and departures are
processed on these runways [4]. Similarly, in IFR conditions the hourly
capacity of a pair of closely spaced parallel runways ranges from
50 to 60 operations per hour, of a pair of intermediate parallel run-
ways from 60 to 75 operations per hour, and for a pair of far parallel
runways from 100 to 125 operations per hour [4].
A dual-lane parallel runway consists of two closely spaced paral-
lel runways with appropriate exit taxiways. Although both runways
can be used for mixed operations subject to the conditions noted
above, the desirable mode of operation is to dedicate the runway far-
thest from the terminal building (outer) for arrivals and the runway
closest to the terminal building (inner) for departures. It is estimated
that a dual-lane runway can handle at least 70 percent more traffic
than a single runway in VFR conditions and about 60 percent more