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Capacity and LOS
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Definitions
• Capacity: Maximum flow through a facility
• Level of service: Quality of service offered by afacility
under prevailing demand-supply
conditions – Different measures for different facility
types – Measure of effectiveness include
• Density
• Delays
• Speed etc.
• Capacity is fixed quantitative value; LOS is aqualitative
variable
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Types of Facilities
• Freeway / Highway segments
– Freeway segments• Basic, weaving, ramps
– Multi-lane highways – Two-lane highway…
• Intersections
– Signalized and Unsignalized• Arterial streets
• Pedestrian walkway
MoE for LOS
Density
Speed / percent time spent followingfor 2-lane highways
Control delay
Speed
Pedestrian density
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Level of Service
• LOS A: Free-flow condition
• LOS B: Mostly free-flow
• LOS C: Near free-flow; local deterioration in
service observed
• LOS D: Speeds drop, effect of even minor
incidents felt upstream
• LOS E: Facility operating at capacity; even minordisruption
has significant longer term effect
• LOS F: Breakdown of flow
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Level of Service
AB C
D
E
F
S p e e d
Volume / Capacity
1.0
FFS
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Level of Service
• Process for determining:
– Find free flow speed
• To be adjusted for several factors
– Find flow rate for analysis
• Again adjusted for several factors
– Determine LOS from Table / Graph
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Basic Freeway Segment
All HCM graphs have been extracted from Khisty and Lall
(2004)
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LOS Criteria
Density is primary
criteria
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Basic Freeway Segment
• Determine FFS
– Speed upto 1300 pcu/h/lane
– Base free flow speed is adjusted for
• Lane width
• Lateral clearance
• Number of lanes
• Interchange density• Analysis flow rate
– Peak 15-min flow rate; adjusted for heavy
vehicles and unfamiliar drivers
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Multi-lane Highway
Procedure very similar
to basic freewaysegments
Access points will
include intersections,
interchanges, and
driveways
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Two lane highway
• Level of service measured by average
travel speed or percent time spent
following
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