Civil Engineering Reference
In-Depth Information
Table 10.5 Trip mobility and trip time trends
—
1980 to 2000
Commuter
trips
1980
1900
% change
(from 1980)
2000
% change
(from 1990)
Trip length
a
8.54 miles
10.65 miles +24.0
12.41
+13.7
Trip time
b
21.7 min
22.4 min
+3.2
25.5 min
+13.8
Average speed
23.6 mph
28.5 mph
+20.7
28.5 mph
0
All trips
Trip length
8.68 miles
9.47 miles +9.1
10.03 miles +5.9
Trip time
21.7 min
23.4 min
+7.8
25.5 min
+9.0
Average speed
24.0 mph
24.3 mph
+1.3
23.6 min
−
2.9
a
Source [
13
p 51]
b
Source [
13
p 101]
10.5.1 All Trips
1980
-
1990: Trip mobility increased more (+9.1 %) than trip time (+7.8 %).
Re
fl
ecting higher trip speed and an small increase travel time budge.
1990
+5.9 %)
however, trip time increased more (+9.0 %)
—
indicating that the travel time
budget increased more than trip mobility.
2000: Trip mobility continued to increase (but at a slower rate
—
-
10.5.2 Commuter Trips
For commuter trips the
findings are even more dramatic:
1980
1990: Trip mobility increased eight times more than trip time (24 % vs.
3.2 %)
-
—
ecting a relatively stable trip time budget, and big gains in mobility
due to higher travel speed (+20.7 %).
re
fl
1990
-
2000: Trip mobility and trip time kept increasing but at a slower pace
(+13.75 % and +13.8 %, respectively).
Possible explanations for the discrepancy between network speed trends and trip
speed trends are as follows:
(1) Network speed is not synonymous to door-to-door trip speed. Network speed
re
ects the performance of the system under observation. It does not measure
the performance of all trip components that affect door-to-door trip speed.
(2) Freeways and other principal arterials are the most congested roads in large
metropolitan areas. However, because they serve only a fraction of the metro
area
fl
c con-
gestion of the entire roadway network that includes collectors and local streets.
(3) Typically, traf
'
s traf
c, their speed performance cannot be the sole indicator traf
c speed on suburban
roads. Greater population and job growth in suburban areas has increased the
growth of vehicle trips in low density areas where traf
c speed on city streets is lower than traf
c speeds are higher,
