Home |
Background | Public Forum 1 (Jan-05)
| Public Forum 2 (May-05) | Submit Comment
WHAT IS “LEVEL OF SERVICE?”
The Level of Service (LOS) of an intersection is a qualitative measure of capacity and operating conditions and is directly related to vehicle delay. LOS is given a letter designation from A to F, with LOS A representing very short delays and LOS F representing very long delays. As a practical consideration, LOS D is considered the limit of acceptable operation in an urban environment. LOS C is the desirable condition. LOS conditions for signalized intersections are shown in Table 1. For unsignalized intersections, the levels of service are shown in Table 2.
Table 1. Level of Service Criteria for Signalized Intersections
|
Level-of-Service (LOS) |
Average Control Delay (seconds/vehicle) |
Description |
|
A |
≤ 10.0 |
Very low vehicle delays, free flow, signal progression extremely favorable, most vehicles arrive during given signal phase.
|
|
B |
10.1 to 20.0 |
Good signal progression, more vehicles stop and experience higher delays than for LOS A.
|
|
C |
20.1 to 35.0 |
Stable flow, fair signal progression, significant number of vehicles stop at signals.
|
|
D |
35.1 to 55.0 |
Congestion noticeable, longer delays and unfavorable signal progression, many vehicles stop at signals.
|
|
E |
55.1 to 80.0 |
Limit of acceptable delay, unstable flow, poor signal progression, traffic near roadway capacity, frequent cycle failures.
|
|
F |
> 80.0 |
Unacceptable delays, extremely unstable flow and congestion, traffic exceeds roadway capacity, stop-and-go conditions.
|
SOURCE:
Highway Capacity Manual, HCM2000, Transportation Research Board, 2000.
Table 2. Level of Service Criteria for Unsignalized Intersections
|
Level-of-Service (LOS) |
Average Control Delay (seconds/vehicle) |
Description |
|
A |
≤ 10.0 |
No delays at intersections with continuous flow of traffic. Uncongested operations: high frequency of long gaps available for all left and right turning traffic. No observable queues.
|
|
B |
10.1 to 15.0 |
Same as LOS A |
|
C |
15.1 to 25.0 |
Moderate delays at intersections with satisfactory to good traffic flow. Light congestion; infrequent backups on critical approaches.
|
|
D |
25.1 to 35.0 |
Increased probability of delays along every approach. Significant congestion on critical approaches, but intersection functional. No standing long lines formed.
|
|
E |
35.1 to 50.0 |
Heavy traffic flow condition. Heavy delays probable. No available gaps for cross-street traffic or main street turning traffic. Limit of stable flow.
|
|
F |
> 50.0 |
Unstable traffic flow. Heavy congestion. Traffic moves in forced flow condition. Average delays greater than one minute highly probable. Total breakdown.
|
SOURCE:
Highway Capacity Manual, HCM2000, Transportation Research Board, 2000.
|
Business20TrafficStudy.com