Capacity Level of Service-transport

8/10/2019 Capacity Level of Service-transport

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Freeway & Highway Level of Service

CETB 414NI-UNITEN


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Chapter

Capacity And Levelof Service


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Outline

1. Definitions2. Level of Service (LOS)3. Freeway Segment LOS Determination

a. Free-flow speedb. Flow Rate


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Freeway Definition

A divided highway with full control ofaccess and two or more lanes for the

exclusive use of traffic in each direction. Assumptions

No interaction with adjacent facilities (streets,other freeways)

Free-flow conditions exist on either side of thefacility being analyzed

Outside the influence or ramps and weaving areas


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Basic Freeway Segment

From Highway Capacity Manual , 2000


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Base / Ideal Condition for Freeway 3.6 m (12 ft) minimum lane widths. 1.8 m (6 ft) minimum clearance between the

edge of travel lanes and the nearest roadsideobstructions.

0.6 m (2 ft) minimum median lateral clearance Traffic stream consists of passenger cars only 10 or more lanes (both direction -in urban area

only)

Interchanges spaced every 3.3 km Level terrain with grades no greater than 2

percent Driver population dominated by regular and

familiar users of the facility (commuter) C E T B

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Free-Flow Speed

Free-Flow Speed (FFS) The mean speed of passenger cars that can be

accommodated under low to moderate flow rateson a uniform freeway segment under prevailingroadway and traffic conditions.

Factors affecting free-flow speed Lane width - Driver population Lateral clearance - Geometric design Number of lanes - Interchange density Vehicle equivalents


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Freeway capacity

The maximum sustained 15-min flow rate,expressed in passenger cars per hour per lane(pc/hr/ln), that can be accommodated by a uniform

freeway segment under prevailing traffic androadway conditions in one direction of flow.

Number of lanesLanes width

Lateral obstructionInterchange spacing

Grade

Traffic compositionDriver population

speed


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Free-Flow Speed

Free-Flow Speed (FFS) The mean speed of passenger cars that can be

accommodated under low to moderate flow rateson a uniform freeway segment under prevailingroadway and traffic conditions.

Factors affecting free-flow speed Lane width - Driver population Lateral clearance - Geometric design Number of lanes - Interchange density Vehicle equivalents ( Trucks and RVs behave differently)


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Definitions Level of Service (LOS) Qualitatively measures both the operating

conditions within a traffic system and howthese conditions are perceived by drivers

and passengers Related to the physical characteristics of the highway

and the different operating characteristic that canoccur when the highway carries different traffic

volumes (Different measures for different facilities)Lane width , lateral obstruction , grade, traffic composition , speed, driverpopulation

Six measures (A through F )


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Levels of Service

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LOS A Free-flow operation with

low volume Density not greater than 7

pc/km/ln High speed

LOS B Reasonably free flow Ability to maneuver is only

slightly restricted Effects of minor incidents

still easily absorbed


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Levels of Service

LOS C Speeds at or near FFS Freedom to maneuver is

noticeably restricted Queues may form behind any

significant blockage.

LOS D

Speeds decline slightly withincreasing flows Density increases more quickly Freedom to maneuver is more

noticeably limited Minor incidents create queuing

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Levels of Service

LOS E Operation near or at capacity No usable gaps in the traffic

stream Operations extremely volatile Any disruption causes queuing

LOS F

Breakdown in flow Queues form behind

breakdown points Demand > capacity

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Freeway LOS


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Freeway LOS

Level of Service


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Freeway LOS


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LOS Calculation

Does not consider Special lanes reserved for a particular type of vehicle

(HOV, truck, climbing, etc.)

Extended bridge and tunnel segments Segments near a toll plaza Facilities with FFS < 90 km/h or > 120 km/h Demand conditions in excess of capacity Influence of downstream blockages or queuing Posted speed limit Extent of police enforcement Intelligent transportation system features Capacity-enhancing effects of ramp metering

Freeway LOS


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InputGeometric Data

Measured FFS or BFFSVolume

BFFS AdjustmentLane width

Number of lanesInterchange density

Lateral clearance

Volume AdjustmentPHF

Number of lanesDriver populationHeavy vehicles

Compute FFS Compute flow rate

Define speed-flow curve

Determine speed using speed-flow curve

Compute density using flow rate and speed

Determine LOS

BFFS Input

MeasuredFFS Input

Freeway LOS

F LOS


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Determining FFS

Measure FFS in the field Low to moderate traffic conditions

Use a baseline and adjust it (BFFS)

ID N LC LW f f f f BFFS FFS FFS = free-flow speed (km/h)

BFFS = base free-flow speed, 110 km/h (urban), 120 km/h (rural)

f LW = adjustment for lane width (km/h)

f LC = adjustment for right-shoulder lateral clearance (km/h)

f N = adjustment for number of lanes (km/h)

f ID = adjustment for interchange density (km/h)

Freeway LOS

F LOS


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Lane Width Adjustment (f LW )

Base condition (f LW = 0) Average width of 3.6 m or wider across all lanes


Freeway LOS

F LOS


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Lateral Clearance Adjustment (f LC )

Base condition (f LC = 0) 1.8 m or greater on left side

0.6 m or greater on the median or right side


Freeway LOS

USA

F LOS


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Number of Lanes Adjustment (f N) Base condition (f N = 0)

5 or more lanes in one direction Do not include HOV lanes

f N = 0 for all rural freeway segments


Freeway LOS

F LOS


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Interchange Density Adjustment (f IC)

Base condition (f IC = 0) 0.3 interchanges per km (3.3 km spacing) Interchange defined as having at least one on-ramp Determined over 10 km segment


Freeway LOS

F LOS


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Determining Flow Rate

Adjust hourly volumes to get pc/ln/hr

p HV p f f N PHF

V v

vp = 15-minute passenger-car equivalent flow rate (pcphpl)

V = hourly volume (veh/hr)PHF = peak hour factor

N = number of lanes in one direction

f HV = heavy-vehicle adjustment factor

f P = driver population adjustment factor

Freeway LOS

Freeway LOS


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Peak Hour Factor (PHF)

Typical values 0.80 to 0.95

Lower PHF characteristic or rural or off-peak Higher PHF typical of urban peak-hour

415V

V PHF

V = hourly volume (veh/hr) for hour of analysis

V15 = maxiumum 15-min. flow rate within hour of analysis

4 = Number of 15-min. periods per hour

Freeway LOS

Freeway LOS


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Heavy Vehicle Adjustment (f HV)

Base condition (f HV = 1.0) No heavy vehicles

Heavy vehicle = trucks, buses, RVs

Two-step process Determine passenger-car equivalents (E T) Determine f HV

Freeway LOS

Freeway LOS


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Determine f HV

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1

R RT T HV E P E P

f

f HV = Heavy vehicle adjustment factor

ET, E R = Passenger-car equivalents for trucks/buses and RVs

P T, P R = Proportion of trucks/buses and RVs in traffic stream

Freeway LOS

Freeway LOS


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Passenger-Car Equivalents (E T)

Extended segments method Determine the type of terrain and select E T No one grade of 3% or more is longer than 0.4 km

OR No one grade of less than 3% is longer than 0.8 km


Freeway LOS

Freeway LOS


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Passenger-Car Equivalents (E T) Specific grades method

Any grade of 3% or more that is longer than 0.4 kmOR

Any grade of less than 3% that is longer than 0.8 km


Freeway LOS

Freeway LOS


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Freeway LOS


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Freeway LOS

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Freeway LOS


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Composite grades method Determines the effect of a series of steep

grades in succession

Method OK if All subsection grades are less than 4%

OR Total length of composite grade is less than 1200 m

Otherwise, use a detailed technique in theHighw ay Capaci ty Manual (HCM)


Freeway LOS

Freeway LOS


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Driver Population Adjustment (f P)

Base condition (f P = 1.0) Most drivers are familiar with the route

Commuter drivers Typical values between 0.85 and 1.00

Freeway LOS

Freeway LOS


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Determining level of Service(LOS)

Directly determine from Speed-Flow curve

Determine the density of flow

Freeway LOS

Freeway LOS


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Define Speed-Flow Curve

Select a Speed-Flow curve based on FFS


Freeway LOS

Freeway LOS


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Determine Average PC Speed (S)

For 90 FFS 120 km/h AND (3100 15FFS) < vp (1800 + 5FFS)

For 90 FFS 120 km/h AND vp < (3100 15FFS)

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310015180023

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FFS

FFS v FFS FFS S p

FFS S

Freeway LOS

Use v p and FFS curve to find average passenger car speed (S)

Freeway LOS


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Determine Density

Calculate density using:

S

v D

p

D = density (pc/km/ln)

vp = flow rate (pc/km/ln)

S = average passenger-car speed (km/h)

Freeway LOS

Freeway LOS


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y

Determine LOS

Freeway LOS


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y

Determine LOS

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Freeway LOS


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Example 1

y

Existing 4-lane freeway, urban area with very restricted geometry.

3.3 m lane width 0.6 m lateral clearance on left and right sides rolling terrain interchange spaced 2 km apart 2000 vph peak hour volume (one direction) PHF = 0.92 Traffic consists of 5% truck Mostly commuter traffic.

Determine the LOS during peak hour.

Freeway LOS


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Example 2

y

Existing rural freeway

v ideal free flow speed of 120 km/hrv has two 3.6m lanes in each directionv 1.2m shoulder lateral clearance v Interchanges spaced approximately 5 km apart.v Traffic consists of 10% trucks and buses and 8%

recreational vehicles.v The adjustment for driver population factor is estimated to

be 0.80.v Peak 15 min flow rate is 1760 vph

Determine the LOS on a 1.7 km long 3.1% upgrade?

Freeway LOS


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Example 3

y

Existing rural freeway

v Ideal free flow speed of 120 km/hrv Rolling terrainv 1.2m shoulder lateral clearance v Interchanges spaced approximately 5 km apart.v Traffic consists of 10% trucks and buses and 8%

recreational vehicles.v The adjustment for driver population factor is

estimated to be 0.80.v Peak 15 min flow rate is 1760 vph

How many lanes to provide LOS B?How many vehicles can be added before the roadwayreaches capacity?


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Primary References

Nicholas J. Garber, Lester A. Hoel (2005). Traffic & HighwayEngineering , Third Edition. Chapter 9

Transportation Research Board. (2000). Highway Capacity Manual2000 . National Research Council, Washington, D.C.

Documents

Capacity Level of Service-transport