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Appendix
A
Level of Service Concepts, Analysis Methodologies,
& Standards of Significance
Appendix A: Level of Service Concepts, Analysis Methodologies, & Standards of Significance | A-1
Traffic Impact Study - Bozeman Gateway PUD, Phase 4 Apartments
March 2021
Unsignalized Intersection Level of Service
The method presented in the Highway Capacity Manual, 6th Edition | A Guide for Multimodal Mobility Analysis (HCM)
published by the Transportation Research Board (TRB) for evaluating unsignalized, stop-controlled intersections is
based on the average total delay for each impeded movement. As used here, total delay is defined as the total
elapsed time from when a vehicle stops at the end of a queue until the vehicle departs from the stop line. This time
includes the time required for the vehicle to travel from the last-in-queue to the first-in-queue position. The average
total delay for any minor movement is a function of the service rate or capacity of the approach and the degree of
saturation. The resulting delay is used to determine the level of service as shown in Table A-1 below.
Table A-1: Level of Service Criteria for Stop-Controlled Intersections
Average Control Delay Level of Service (LOS) Characteristics
10 seconds A Little or no delay
10.0 – 15.0 seconds B Short traffic delay
15.0 – 25.0 seconds C Average traffic delay
25.0 – 35.0 seconds D Long traffic delays
35.0 – 50.0 seconds E Very long traffic delays
> 50.0 seconds F
When the demand exceeds the capacity of the lane, extreme
delays will be encountered, and queuing may cause severe
congestion to the intersection.
Source: Highway Capacity Manual, 6th Edition | A Guide for Multimodal Mobility Analysis (Transportation Research Board, 2016)
Figure A-16: Control Delay and Flow Rate
Source: Highway Capacity Manual 2000,
Page 17-24
(Transportation Research Board, 2000)
A-2 | Appendix A: Level of Service Concepts, Analysis Methodologies, & Standards of Significance
Traffic Impact Study - Bozeman Gateway PUD, Phase 4 Apartments
March 2021
Signalized Intersection Level of Service
The operational analysis method for signalized intersections presented in the HCM defines level of service in terms
of delay, or more specifically, control stopped delay per vehicle. Delay is a measure of driver and/or passenger
discomfort, frustration, fuel consumption, and lost travel time. The level of service criteria for signalized
intersections is presented in Table A-2 below:
Table A-2: Level of Service Criteria for Signalized Intersections
Average Control Delay Level of Service (LOS) Characteristics
10 seconds A
Operations with very low delay. This occurs when progression is
extremely favorable, and most vehicles do not stop at all. Short
cycle lengths may also contribute to low delay.
10.0 – 20.0 seconds B
Operations with generally good progression and/or short cycle
lengths. More vehicles stop than for LOS A, causing higher levels
of average delay.
20.0 – 35.0 seconds C
Operations with higher delays, which may result from fair
progression and/or longer cycle lengths. Individual cycle failures
may begin to appear at this level. The number of vehicles
stopping is significant at this level, although many still pass
through the intersection without stopping.
35.0 – 55.0 seconds D
Operations with high delay, resulting from some combination of
unfavorable progression, long cycle lengths, or high volumes. The
influence of congestion becomes more noticeable, and individual
cycle failures are noticeable.
55.0 – 80.0 seconds E Considered being the limit of acceptable delay. Individual cycle
failures are frequent occurrences.
> 80.0 seconds F
A condition of excessively high delay considered unacceptable
to most drivers. This condition often occurs when arrival flow
rates exceed the capacity of the intersection. Poor progression
and long cycle lengths may also be major contributing causes
to such delay.
Source: Highway Capacity Manual, 6th Edition | A Guide for Multimodal Mobility Analysis (Transportation Research Board, 2016)