Civil Engineering Reference
In-Depth Information
12.3.2 Skycomp Analysis
An example showing what happens to freeway speed when traf
c density increases
beyond critical density (D
c
), was captured through aerial surveys of freeways and
expressways in the New York City area by Skycomp (5). These patterns are shown
in Fig.
12.4
.
From Skycomp
c
density were developed to illustrate (1) the impact of increasing traffic density
beyond its critical value of 45 pcplpm, on traf
'
s observations, correlations between traf
c speed and traf
c
speed on productivity (throughput volume) at speeds lower than the critical value of
53 mph. The results are shown in Fig.
12.5
through Fig.
12.8
.
c speed; and (2) the impact of traf
Figure
12.5
shows how freeway speeds decrease once the critical density of
45 vehicles per lane per mile is exceeded.
Figure
12.6
shows the entire speed-density relationship. In the example the
density of 45 passenger cars per lane per mile separates the regions of uncon-
gested and congested
fl
ow. The speed
—
density data for uncongested
fl
ow was
calculated from Fig.
12.1
.
Fig. 12.4 Correlation of speed to vehicle density obtained through aerial surveys.
Source
References [
4
], p 96, Fig. 27 and [
5
]
