Civil Engineering Reference
In-Depth Information
Table 8.5
Minimum desirable travel standards suggested by the national committee on urban
transportation
a
Peak hour
Off-peak
Type of roadway
Average
speed
(miles/h)
Travel time
rate (min/mile)
Average
speed
(miles/h)
Travel time
rate
(min/mile)
Freeway or expressway
35
1.71
35
50
1.20
1.71
-
-
Major arterial
25
2.40
25
35
1.71
2.40
-
-
Collector
20
3.00
20
-
25
2.40
-
3.00
Local streets
10
6.00
10
20
3.00
6.00
-
-
a
No longer existent
8.3.2 Suggested Congestion Delay Standards from NCHRP
Research Report 398 [
6
]
Delay standards in Table
8.5
further streamlined in this report recognizing that
traveler expectations of traf
c conditions depend on the size of urban areas. The
resulting guidelines are shown in Table
8.6
.
8.3.3 The 2010 Highway Capacity Manual Criteria
The 2010 Highway Capacity Manual [
17
] establishes the
“
Level of Service
”
(LOS)
standards for various types of roadways. The standards range from
“
A
”
(free-
fl
ow)
to
flow). Factors included in establishing levels of service are: (1)
speed and travel time, (2) traf
“
F
”
(congested
fl
c interruptions (delays), (3) freedom to maneuver, (4)
safety, and (5) driving comfort and convenience.
How density affects freeway operating speeds is illustrated in Fig.
8.6
. As shown,
when density exceeds 45 passenger cars per lane per mile, speeds drop rapidly, and
the
flow rate drops as well. At their critical density (corresponding to the value
producing maximum throughput volume), travel times are about 1.15
fl
1.20 times
-
greater than the free-
fl
flow travel times. However, at its critical density, traf
c
fl
ow
Table 8.6
Suggested congestion delay standards for various sizes of urbanized areas
Functional classification
Small urban
communities
Mid sized urban
areas
Large urban
areas
Expressways-freeways
1.0
1.2 min/mile
1.3
1.5 min/mile
1.7
2.0 min/mile
-
-
-
(50
-
60 mph)
(40
-
45 mph)
(30
-
35 mph)
Class I Arterials
a
1.7
2.0 min/mile
2.4
3.0 min/mile
3.0
4.0 min/mile
-
-
-
(30
35 mph)
(20
25 mph)
15
20 mph)
-
-
-
Class II/III Arterials
b
2.4
3.0 min/mile
3.0
4.0 min/mile
4.0
6.0 min/mile
-
-
-
(20
25 mph)
(15
20 mph)
(10
15 mph)
-
-
-
a
High type arterials with free-flow speeds of 30
-
35 mph
b
Other arterials with free-flow speeds of 20
-
25 mph
