Page 216 - Planning and Design of Airports

Geometric Design of the Airfield 181

traffic than a single runway in IFR conditions. It is recommended that
the two runways be spaced not less than 1000 ft apart (1200 ft, where
particularly larger wingspan aircraft are involved). This spacing also
provides sufficient distance for an arrival to stop between the two
runways. A parallel taxiway between the runways will provide for a
nominal increase in capacity, but is not essential. The major benefit of
a dual-lane runway is to provide an increase in IFR capacity with
minimal acquisition of land [7, 14].

Intersecting Runways
Many airports have two or more runways in different directions cross-
ing each other. These are referred to as intersecting runways. Intersect-
ing runways are necessary when relatively strong winds occur from
more than one direction, resulting in excessive crosswinds when only
one runway is provided. When the winds are strong, only one runway
of a pair of intersecting runways can be used, reducing the capacity of
the airfield substantially. If the winds are relatively light, both run-
ways can be used simultaneously. The capacity of two intersecting
runways depends on the location of the intersection (i.e., midway or
near the ends), the manner in which the runways are operated for
takeoffs and landings, referred to as the runway use strategy, and the
aircraft mix. The farther the intersection is from the takeoff end of the
runway and the landing threshold, the lower is the capacity. The high-
est capacity is achieved when the intersection is close to the takeoff
and landing threshold. Figure 6-3 provides an example of intersecting
runways with the intersection closer to the runway thresholds.

Open-V Runways
Runways in different directions which do not intersect are referred
to as open-V runways. This configuration is shown in Fig. 6-4. Like
intersecting runways, open-V runways revert to a single runway
when winds are strong from one direction. When the winds are light,
both runways may be used simultaneously.
The strategy which yields the highest capacity is when operations
are away from the V and this is referred to as a diverging pattern. In
VFR the hourly capacity for this strategy ranges from 60 to 180 opera-
tions per hour, and in IFR the corresponding capacity is from 50 to 80
operations per hour [4]. When operations are toward the V it is referred
to as a converging pattern and the capacity is reduced to 50 to 100
operations per hour in VFR and to between 50 and 60 operations per
hour in IFR [4].

Combinations of Runway Configurations
From the standpoint of capacity and air traffic control, a single-direction
runway configuration is most desirable. All other things being equal,