This module focuses on Capacity concepts and the Level of Service for transportation facilities. LOS analysis will be discussed for the multilane highway facility.

1. Capacity Analysis &
Level of Service
A- Capcity Concept
B- Level of Service
C- Multilane Highway
LOS

2. Background:
 The first edition of the HCM was published by the then Bureau of Public Roads in
1950.
 The second edition was published in 1965. It introduced significant new material
on limited access facilities, as well as the level-of-service concept(LOS).
 The third edition was published in 1985, providing refinements to the level-of-
service (LOS) concept and adding material on pedestrian and transit facilities.
 The fourth edition referred to as HCM 2000, which the current material is based
on:
HCM primary objectives were:
I. To provide uniform guidelines for the nation’s rapidly growing highway
construction program.
II. To assure Efficiency and Equity in among transportation infrastructure users in
the states.
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3. The Capacity Concept:
The Highway Capcity Manual (HCM 2000) defines
Capacity as following:
“The capacity of a facility is the maximum hourly
rate at which persons or vehicles reasonably can be
expected to traverse a point or a uniform section of
a lane or roadway during a given time period under
prevailing roadway, traffic, and control conditions.”
HCM2000 , pp. 2-2
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4. Concept #1 in HCM Capacity Definition
Capacity is defined as a maximum hourly rate.
For most cases, the rate used is for the peak 15
minutes of the peak hour, although HCM 2000 allows
for some discretion in selecting the length of the
analysis period. In any analysis, care must be taken to
express both the demand and the capacity in terms
of the same analysis period.
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5. Capacity may be expressed in terms of
persons or vehicles:
 This is critical when transit and pedestrian issues are
considered, as well as in the consideration of high-
occupancy vehicle (HOV) lanes and facilities, where the
person-capacity is clearly more important than the vehicle-
capacity.
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Concept #2 in HCM Capacity Definition

6. Capacity is defined for prevailing roadway, traffic, and control
conditions.
 Roadway conditions refer to the geometric characteristics of the
facility, such as the number of lanes, lane widths, shoulder widths,
and free-flow speeds.
 Traffic conditions refer primarily to the composition of the traffic
stream, particularly the presence of trucks and other heavy
vehicles.
 Control conditions refer primarily to interrupted flow facilities, where
such controls as STOP and YIELD signs and traffic signals have a
significant impact on capacity.
 The important concept is that a change in any of the prevailing
conditions causes a change in the capacity of the facility.
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Concept #3 in HCM Capacity Definition

7. Capacity is defined for a point or uniform section of a
facility:
This correlates to the “prevailing conditions” discussed
above. A “uniform section” must have consistent
prevailing conditions. At any point where these
conditions change, the capacity also changes.
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Concept #4 in HCM Capacity Definition

8. Capacity refers to maximum flows that can “reasonably” be
expected to traverse a section:
 This recognizes that capacity is subject to variation in both time
and space. Thus, capacity is not defined as the single highest
flow level ever expected to occur on a facility. Rather it is a value
that represents a flow level that can be reasonably achieved
repeatedly at a given location and at similar locations
throughout the United States. Thus, isolated observations of
actual flows in excess of stated capacities is not a contradiction
and is, in fact, an expected condition.
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Concept #5 in HCM Capacity Definition

9. Level of Service (LOS) Concept:
 The level-of-service concept was introduced in the 1965 HCM as a
convenient way to describe the general quality of operations on a
facility with defined traffic, roadway, and control conditions.
 Using a letter scale from A to F, a terminology for operational quality
was created that has become an important tool in communicating
complex issues to decision-makers and the general public.
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10. Level of Service (LOS) Concept:
 The Highway Capcity Manual (HCM 2000) defines Level Of Service
(LOS) as following:
“Level of service (LOS) is a quality measure describing operational
conditions within a traffic stream, generally in terms of such service
measures as speed and travel time, freedom to maneuver, traffic
interruptions, and comfort and convenience.”
(HCM 2000, pg. 2-2).
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11. Critical Issues with LOS Concept:
 When originally defined, models did not exist for the prediction of
precise quality measures for many types of facilities. This is no longer
true. Every facility type now has levels of service defined in terms of
a specific measure of effectiveness.
 Levels of service are basically step-functions, each representing a
range of operating conditions. Levels of service B and C, for
example, may represent very similar conditions if they are both
close to the defined boundary between the two levels.
 Example:
 Site S1 LOS=B
 Site S2 LOS=B
 Site S3 LOS=C
 But S2 &S3 almost
the same
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A C
B D E F
S1 S2 S3

12. Critical Issues with LOS Concept (Cont.):
 Another critical concept is that level of service is to be defined in
terms of parameters that can be perceived by drivers and
passengers and that the definitions should reflect that perception.
 Thus, volume or flow is never used as a measure of
effectiveness, as it is a point measure that cannot be perceived
by drivers or passengers from within the traffic stream.
 On the other hand, it is very difficult to measure driver or
passenger perceptions regarding specific threshold values.
 Thus, most level-of-service criteria are based on the collective
judgment of professionals, exercised through the Highway
Capacity and Quality of Service Committee and its
subcommittees.
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13. Measures for Level of Service (LOS):
Common Service Measures used in LOS:
1. Speed,
2. Travel Time /delay
3. Freedom to maneuver / traffic density
4. Traffic interruptions
5. Comfort & Convince
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14. Measures of Effectiveness for (LOS):
 LOS is usually defined in terms of parameters that can be
perceived by drivers and passengers:
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15. LOS & Service Flow Rate Concept:
Service Flow Rate:
 A service flow rate is similar to capacity, except that it represents
the maximum flow rate that can be accommodated while
maintaining a designated level of service.
 Service flow rates may be defined for levels of service A-E, but are
never defined for level of service F, which represents unstable flow
or unacceptably poor service quality.
 Due to the complexity of some capacity and level-of-service
models, service flow rates are difficult to determine for some types
of facilities.
 Like capacity, service flow rates are defined for prevailing
conditions on uniform sections of a facility, and they relate to flow
levels that can be reasonably expected to occur at the various
levels of service.
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16. Problems of Level of Service(LOS)
The MOST significant problem with LOS, is the ability to misinterpret
changes in level of service due to the step-function nature of the
concept, has already been noted.
Other Key Problems:
 A single set of LOS criteria different levels of perception
What might be acceptable delay at an intersection in Dammam City,
for example, might not be acceptable at a similar intersection in a small
community.
 Some state and local governments have incorporated level-of-service
criteria into development legislation. Thus, when revisions to the HCM
are made, legal standards are being altered. This is clearly not the intent
of the HCQSC, and it is not generally recognized by the legislators
enacting these laws.
 In 1985, the adoption of delay as a level-of-service measure for
signalized intersections introduced new complexity to the interpretation
of level of service F. For some types of facilities, this designation
indicates a situation in which demand exceeds capacity. For other
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17. Other Performance Measures:
The v/c Ratio &its Use in Capacity
Analysis
The v/c ratio:
Is defined as the ratio between current or
projected traffic demand flow to the
capacity of the facility.
This ratio is used as a measure of capacity
sufficiency for existing or proposed facilities.
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18. Level of Service
for Multilane Highway
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19. Highway Capacity
Levels of Service (LOS)
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Source: Maryland DOT http://www.mdta.maryland.gov/

20. Highway Capacity
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Source:
Source: Maryland DOT http://www.mdta.maryland.gov/

21. Cross Sectional Elements (Ch. 4)
 AASHTO Defines two main Elements:
 Roadway: The portion of a highway, including shoulders, for vehicular use.
A divided highway has two or more roadways .
 Traveled Way: The portion of the roadway for the movement of vehicles,
exclusive of shoulders.
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22. ElDessouki
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23. ElDessouki
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24. ElDessouki
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25. Highway Capacity
HCM Standard Conditions (Multilane Rural Highway):
 3.6-m minimum lane widths;
 Only passenger cars in the traffic stream;
 No direct access points along the roadway;
 A divided highway; and
 Free-flow speed (FFS) higher than 100 km/h.
 3.6-m minimum total lateral clearance in the
direction of travel -- ( this represents the total
lateral clearances from the edge of the traveled
lanes to obstructions along the edge of the road
and in the median (in computations, lateral
clearances greater than 1.8 m are considered in
computations to be equal to 1.8 m);
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26. Highway Capacity Analysis
HCM Methodology:

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27. Highway Capacity Analysis
HCM Methodology (cont.):
 Volume Adjustment :
( converting traffic volume into passenger cars
equivalent)
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28. Highway Capacity Analysis
HCM Methodology (cont.):
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29. Highway Capacity Analysis Cases
Operational Case: Existing Facility
Design Input:
Number of Lanes
Lane Width
Median
Shoulders
Traffic Volume
Topography (i.e. Terrain: Level /Rolling/ Mountainous)
HV%, PHF ,
Design Objective:
Current Level Of Service (LOS)
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30. Highway Capacity Analysis Cases
Design Case 1: New Construction
Design Input:
Design Volume
Target LOS
Topography (i.e. Terrain: Level /Rolling/ Mountainous)
Right of Way (ROW)
Design Objective:
Number of Lanes (N)
Lane Width
Median
Shoulders
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31. Highway Capacity Analysis Cases
Design Case 2: New Construction
Design Input:
Number of Lanes
Lane Width
Median
Shoulders
Design LOS
Topography (i.e. Terrain: Level /Rolling/ Mountainous)
Projected HV%, PHF ,
Design Objective:
Maximum Service Volume for the given design LOS (Vp)
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32. End of Module 1
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