Civil Engineering Reference
In-Depth Information
Comment
:
For large metropolitan areas this de
nition usually exaggerates the amount of
congestion delay calculated for the peak hours of traf
c
fl
flow, because it assumes
that it would be possible to travel at free
flow-speeds during the peak hours.
The delay rate also can be used for city streets by comparing the actual off peak
and peak travel times. A pioneer study of congestion in the Chicago central busi-
ness district (conducted during the 1950s) illustrates this approach. The study
compared auto and transit travel times in the north
fl
south direction, across the one
square mile loop, on a Sunday morning with those during the working day. The
results are shown in Table
8.2
.
Average auto travel times during weekdays were 50 % higher compared to Sunday
morning travel times (6 vs. 4 min). For bus transit they were 44 % higher. The
corresponding delay rates were 2.0 min/mile for auto, and 2.5 min/mile for bus transit.
-
8.2.1.2 Vehicle-Hours of Delay
The average peak hour, daily and annual vehicle hours of delay can be obtained by
aggregating the delay incurred in various roadway sections in each direction.
Annual delays can be obtained by aggregating the daily delays incurred.
The national reporting of congestion trends by the annual Urban Mobility Report
[
9
] publishes the amounts of hours lost annually by commuters from various cities.
This delay is calculated by the following equation:
Daily Vehicle
Hours of Delay
ð
DVHD
Þ
¼½
daily vehicle
minutes at actual speed
ð
8
:
2
Þ
½
daily vehicle
minutes at free
flow speed
Table 8.2
North
South auto and transit speeds and travel times (one-mile distance) in Chicago
'
s
-
central business district, 1950
Auto
Speed (mph)
Travel time (min)
Possible (Sunday morning)
12.1
4
Actual working day
7.5
6
Difference
4.6
2
Delay rate
2 min/mile
Transit
Speed (mph)
Travel time (min)
Possible (Sunday morning)
8
5.5
Actual working day
5.4
8
Difference
2.6
2.5
Delay rate
2.5 min/mile
Source
Reference [
12
], multiple pages
