cee 320 spring 2008 level of service and design traffic volumes cee 320 kelly pitera

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8Level of Service and Design Traffic Volumes

CEE 320Kelly Pitera

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Outline

1. Freeway Segment LOS Determinationa. Free-flow speed

b. Flow Rate

2. Multilane Highway LOS

3. Design Traffic Volume

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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 < 55 mi/h or > 75 mi/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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Geometric DataMeasured FFS or BFFS

Volume (highest)

BFFS AdjustmentLane width

Number of lanesInterchange densityLateral clearance

Volume AdjustmentPHF

Number of lanesDriver populationHeavy vehicles

Compute FFS Compute flow rate

Determine S from speed-flow curve

Determine LOS

Compute density using flow rate and speed

Check on speed-flow curve

BFFS Input

Measured FFS Input

Freeway LOS

If FFS notknown

Adjust for temporal variation

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Determining FFS

• Measure FFS in the field– Low to moderate traffic conditions

• Use a baseline and adjust it (BFFS)

IDNLCLW ffffBFFSFFS FFS = free-flow speed (mph)

BFFS = base free-flow speed, 70 mph (urban), 75 mph (rural)

fLW = adjustment for lane width (mph)

fLC = adjustment for right-shoulder lateral clearance (mph)

fN = adjustment for number of lanes (mph)

fID = adjustment for interchange density (mph)

Freeway LOS

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Base conditions for basic freeway segment

• 12-ft lane widths• 6-ft right shoulder• 2-ft median lateral clearance• Only passenger cars• 5 or more lanes in each travel direction• 2-mi or greater interchange spacing• Level terrain• Mostly familiar roadway users

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Lane Width Adjustment (fLW)

• Base condition (fLW = 0)– Average width of 12 ft. or wider across all lanes

– Table 6.3 in text

From Highway Capacity Manual, 2000

Freeway LOS

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Lateral Clearance Adjustment (fLC)

• Base condition (fLC = 0)– 6 ft. or greater on right side– 2 ft. or greater on the median or left side



Freeway LOS

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Number of Lanes Adjustment (fN)

• Base condition (fN = 0)– 5 or more lanes in one direction

– Do not include HOV lanes

– fN = 0 for all rural freeway segments



Freeway LOS

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Interchange Density Adjustment (fID)

• Base condition (fID = 0)– 0.5 interchanges per mile (2-mile spacing)– Interchange defined as having at least one on-ramp– Determined over 6-mile segment



Freeway LOS

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Determining FFS


IDNLCLW ffffBFFSFFS FFS = free-flow speed (mph)

BFFS = base free-flow speed, 70 mph (urban), 75 mph (rural)


fLC = adjustment for right-shoulder lateral clearance (mph)

fN = adjustment for number of lanes (mph)

fID = adjustment for interchange density (mph)

Freeway LOS

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Volume (highest)







Determine LOS



BFFS Input

Measured FFS Input

Freeway LOS

If FFS notknown


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Determining Analysis Flow Rate

• Adjust hourly volumes to get pc/ln/hr

pHVp ffNPHF

Vv

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

V = hourly volume (veh/hr) highest, total one direction

PHF = peak hour factor

N = number of lanes in one direction

fHV = heavy-vehicle adjustment factor

fP = driver population adjustment factor

Freeway LOS

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Peak Hour Factor (PHF)

• Typical values– 0.80 to 0.95– Lower PHF characteristic of rural or off-peak– Higher PHF typical of urban peak-hour

415 V

VPHF

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

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

4 = Number of 15-min. periods per hour

Freeway LOS

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Heavy Vehicle Adjustment (fHV)

• Base condition (fHV = 1.0)– No heavy vehicles– Heavy vehicle = trucks, buses, RVs

• Two-step process– Determine passenger-car equivalents (ET, ER) for

this traffic stream

– Determine fHV

Freeway LOS

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Passenger-Car Equivalents (ET,ER)

• Extended segments method– Determine the type of terrain and select ET,ER

• Level, rolling, mountainous

– No one grade of 3% or more is longer than 0.25 miles OR

– No one grade of less than 3% is longer than 0.5 miles



Freeway LOS

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Passenger-Car Equivalents (ET)

• Specific grades method– Any grade of 3% or more that is longer than 0.25 miles

OR– Any grade of less than 3% that is longer than 0.5 miles


Freeway LOS

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Freeway LOS

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Passenger-Car Equivalents (ER)

Freeway LOS

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Passenger-Car Equivalents (ET,ER)

• Composite grades method– Determines the effect of a series of steep

grades in succession– Distance weighted average– Method OK if…

• All subsection grades are less than 4%OR

• Total length of composite grade is less than 4000 ft.

– Otherwise, use a detailed technique in the Highway Capacity Manual (HCM)


Freeway LOS

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Determine fHV

111

1

RRTTHV EPEPf

fHV = Heavy vehicle adjustment factor

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

PT, PR = Proportion of trucks/buses and RVs in traffic stream

Freeway LOS

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Driver Population Adjustment (fP)

• Base condition (fP = 1.0)– Most drivers are familiar with the route

• Commuter drivers

• Typical values between 0.85 and 1.00– Analyst selects the value using judgement– Dependent on local conditions (scenic views, etc.)

Freeway LOS

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Determining Analysis Flow Rate


pHVp ffNPHF

Vv


V = hourly volume (veh/hr) highest, total one direction





Freeway LOS

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Volume (highest)







Determine LOS



BFFS Input

Measured FFS Input

Freeway LOS

If FFS notknown


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Define Speed-Flow Curve

Select a Speed-Flow curve based on FFS


Freeway LOS

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Determine Average PC Speed (S)

For 70 < FFS ≤ 75 mph AND (3400 – 30FFS) < vp ≤ 2400

For 55 < FFS ≤ 70 mph AND (3400 – 30FFS) < vp ≤ (1700 + 10FFS)

For 55 < FFS ≤ 75 mph AND vp < (3400 – 30FFS)

6.2

100030

340030

3

160

FFS

FFSvFFSFFSS p

6.2

170040

3400303407

9

1

FFS

FFSvFFSFFSS p

FFSS

Freeway LOS

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Volume (highest)







Determine LOS



BFFS Input

Measured FFS Input

Freeway LOS

If FFS notknown


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Determine Density

• Calculate density using:

S

vD p

D = density (pc/mi/ln)

vp = flow rate (pc/hr/ln)

S = average passenger-car speed (mph)

Freeway LOS

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DetermineLOS

Freeway LOS

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Define Speed-Flow Curve

Select a Speed-Flow curve based on FFS


Freeway LOS

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Example

Geometry• 11 ft. lane width• 2 lanes• Left lateral clearance = 5 ft.• Right lateral clearance = 4 ft.

Other• SR 520• 7 am PHF = 0.95• 2% trucks• 3% buses

Determine the typical LOS for a 6 mile stretch of roadway with 5 interchanges.

Freeway LOS

Determine free flow speed, analysis flow rate

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Determine FFS (fLW)

• FFS = BFFS – fLW – fLC – fN – fID

• BFFS is 70 mph for urban freeway• Given 11 ft lanes

• fLW = 1.9

Freeway LOS

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Determine FFS (fLC )

Freeway LOS


• Given 2 lanes, 4ft right clr

• fLC = 1.2

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Determine FFS (fN)


• Given: 2 lanes

• fN = 4.5

Freeway LOS

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Determine FFS (fID)

In a 6-mile stretch there are 5 interchanges

Freeway LOS

5/6=.833Linear interpolation: (1-.75)/(1-0.833)=(2.5-1.3)/(2.5-x); x = 2.05


• fID = 2.1

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Determine FFS

• FFS = BFFS – fLW – fLC – fN – fID• FFS = 70 – 1.9 – 1.2 – 4.5 – 2.1 = 60.3 mph

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Example

Geometry• 11 ft. lane width• 2 lanes• Left lateral clearance = 5 ft.• Right lateral clearance = 4 ft.

Other• SR 520• 7 am PHF = 0.95• 2% trucks• 3% buses

Determine the typical LOS the a 6 mile stretch of roadway with 5 interchanges.

Freeway LOS

FFS = 60.3 mph

pHVp ffNPHF

Vv

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8 At 7am the ½ hour volume is about 4000 veh/hrAssume half in each direction, 4000 veh/hr max

Graph from the Puget Sound Regional Council’s Puget Sound Trends, No. T6, July 1997

Determine Flow Rate (V)

Freeway LOS

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Determine Flow Rate (vp)

• ET = 1.5, ER = 1.2• Assume there are no RVs

• fHV = 1/(1+PT(ET-1) + PR(ER-1)• fHV = 1/(1+0.05(1.5-1) + 0(1.2-1) = 0.9756

• Assume commuters, therefore fP = 1.00• Vp = V/ (PHF*N*fHV*fP)• Vp = 4000 vph / (0.95)(2)(0.9756)(1.00) = 2158 pcplph

Freeway LOS

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Determine LOS

Freeway LOS

FFS = 60 mph, Vp = 2158 pcplph,S = about 56 mph, Looks like LOS E, Density = 2158/56 = 39 pc/mi/ln

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Freeway LOS

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Multilane Highway LOS

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• Similar to Freeway LOS• A few minor differences


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Free Flow Speed (FFS)

• Measure FFS in the field– Low to moderate traffic conditions


AMLCLW ffffBFFSFFS FFS = free-flow speed (mph)

BFFS = base free-flow speed, 60 mph is typically used


fLC = adjustment for lateral clearance (mph)

fM = adjustment for median type (mph)

fA = adjustment for access points (mph)


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Base Conditions for Multilane Highway

• Level terrain, with grades no greater than 2 percent• Minimum lane width = 12 ft • Objects no closer than 6 ft from the edge of the traveled

pavement (at the roadside or median)• No direct access points along the roadway• Divided highway• Traffic stream composed entirely of passenger cars• Free flow speed of 60 mph or more• Driver population composed principally of regular users


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Lane Width Adjustment (fLW)

• Base condition (fLW = 0)– Average width of 12 ft. or wider across all lanes



Same as Freeway LOS

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Lateral Clearance Adjustment (fLC)

• Base condition (fLC = 0)

– 12 ft or greater TLC

• LCL = 6 ft for undivided highways

– (accounted for in median type adjustment)

• LCL = 6 ft for two-way left-turn lanes

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LR LCLCTLC

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Median Adjustment (fM)

• Base condition (fM = 0)– Divided highway



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Access-Point Density Adjustment (fA)

• For each access point/mi FFS decreases by 0.25 mph

• Base condition (fA = 0)

– 0 access points per mile

• For NAPM ≤ 40: fA = 0.25 × NAPM

• For NAPM > 40: fA = 10



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Determining Flow Rate


pHVp ffNPHF

Vv


V = hourly volume (veh/hr)






Same as Freeway LOS

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• Extended segments method– Determine the type of terrain and select ET

– No one grade of 3% or more is longer than 0.5 miles OR

– No one grade of less than 3% is longer than 1 mile



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• Specific grades method– Any grade of 3% or more that is longer than 0.5 miles

OR– Any grade of less than 3% that is longer than 1 mile



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Determine Average PC Speed (S)

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



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LOS Criteria for Multilane Highways


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Design Traffic Volumes

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Design Traffic Volumes

• Need to select the appropriate hourly traffic volume to get the design LOS

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Definitions

• Annual average daily traffic (AADT)– Annual traffic averaged on a daily basis

• Design hourly volume (DHV)– Traffic volume used for design calculations– Typically between the 10th and 50th highest volume hour

of the year (30th highest is most common)

• K-factor– Relationship between AADT and DHV

AADT

DHVK

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Definitions

• Directional distribution factor (D)– Factor reflecting the proportion of peak-hour traffic

traveling in the peak direction– Often there is much more traffic in one direction than

the other

• Directional design-hour volume (DDHV)

AADTDKDDHV

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Typical Graph

Hou

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AA

DT

Number of hours (annually) withspecified or greater volumes

20 40 10060 8000.10

0.15

0.14

0.13

0.12

0.11

Highest 100 Hourly Volumes Over a One-Year Period for a Typical Roadway

K30=0.12

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Example

• Freeway• PC only facility• AADT = 35,000 veh/day• FFS = 70 mph

Number of lanes required to provide at least LOS C using the 30th highest annual hourly volume?

pHVp ffNPHF

Vv

• Commuters• D = 65% (PH traffic in peak dir.)• PHF=0.85

AADTDKDDHV

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Example

AADTDKDDHV

K = 0.12 (graph)D = 0.65 (given)AADT = 35,000 (given)

000,3565.012.0 DDHV

hrvehDDHV /_2730

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Example

pHVp ffNPHF

Vv

V = 2730 (previous slide)PHF = 0.85 (given)N = 2 (assume 4-lane freeway)fHV = 1.0fP = 1.0

lanehpcvp //_9.1605

From Table 6.1 in text, maximum flow rate for FSS = 70mph and LOS C is 1770 pc/h/lane. 1606 pc/h/lane < 1770 pc/h/lane, therefore 4-lane freeway (2 lanes each direction) is okay.

cee 320 spring 2008 level of service and design traffic volumes cee 320 kelly pitera

Documents

number of lanes mph

input freeway los

mph rural f lw

freeflow speed mph bffs

lane width mph f lc

mph urban

base freeflow speed

hov lanes f n