Freeways and multilane highways
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Freeways and Multilane Highways. CTC-340. HMWK. Ch 13 Read Section 13.7 Ch 13 # 2, 3 Ch 14# 1, 4, 5, 6, 8. Capacity. HCM2000 definition

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Freeways and Multilane Highways

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Freeways and multilane highways

Freeways and Multilane Highways

CTC-340


Freeways and multilane highways

HMWK

  • Ch 13 Read Section 13.7

  • Ch 13 # 2, 3

  • Ch 14# 1, 4, 5, 6, 8


Capacity

Capacity

  • HCM2000 definition

    • The capacity of a facility is the maximum hourly rate at which persons or vehicles can reasonably be expected to traverse a point on a uniform section of a lane or roadway during a given period of time under prevailing roadway, traffic and control conditions


Freeways and multilane highways

LOS

  • LOS

    • Table 13-1 MOEs

  • Service Flow

    • Max flow for a given LOS

  • v/c ratio – ratio of flow to capacity of facility

    • Should be <1

    • If v/c > 1 => congestion


Freeways

Freeways

  • Pure uninterrupted flow

    • Cars enter and exit via ramps

    • No at grade intersections, driveways etc

  • Based on number of lanes


Multilane highways

Multilane Highways

  • Only uninterrupted flow if signals at least 2 miles apart

  • Classified by lanes and median type

  • F 14.1


Freeways and multilane highways

LOS

  • MOE is density – pc/ln/mi

  • Capacity = 45pc/ln/mi

    • Freeways

    • multilane hwys => 40 - 45pc/ln/mi

    • F 14.2, 14.3, T 14.1

  • LOS pg 286 - 290


Freeway analysis

Freeway Analysis

  • F14.2 & 14.3

  • Operational Analysis

    • How is the existing facility operating

    • vp = V/(PHF*N* fHV * fp ) = pc/hr/ln

    • vp is the demand flow rate under ideal conditions

    • With vp can find FFS from curves F 14.2

    • fp= user population

    • If V = 4600vph, PHF = 0.90, N =3, fHV =0.87, fp = 1

    • What is LOS

    • v= 1958pc/h/ln => LOS =? F 14.2 &3


Freeways and multilane highways

  • Service Flow Rate & Service Vol Analysis

  • SFi = MSFi*N*fHV*fp

    • Can find service flow for each LOS i

      • Use Tables 14.3 or 14.4 to get MSF


Freeways and multilane highways

  • Design Analysis

    • Used to determine # of lanes needed for freeway

    • To determine the number of lanes

    • N = DDHV/(PHF*MSF*fHV*fp)

    • Iterative process

    • Number of lanes depends on design speed

    • Design speed depends on # of lanes


Free flow speed freeways

Free Flow Speed - Freeways

  • Free Flow Speed

    • Found when volume < 1000vph/l

    • FFS = BFFS-fLW - fLC – 3.22TRD^0.84

    • fLW – lane width adjustment T14.5

    • fLC – lateral clearance T14.6

      • 6’ on right side 2’ on left

      • Factor only takes right side into account

    • TRD–total ramp density T14.8

      • Total ramps within 3 miles of midpoint of study area/6miles


Multilane highways1

Multilane Highways

  • FFS = BFFS-fLW - fLC - fM – fA

  • fLW – lane width adjustment T14.5

  • fLC – lateral clearance T14.7

  • Greatest LC = 6 feet on both sides

    • Undivided Hwys – no median side clearance – taken into account with fM – assume 6’ clearance

    • TWLTL – assume 6’ clearance

    • Divided hwy – based on median, dist to opposing traffic, periodic objects(light poles) never more than 6’

  • fM –median type T 14.8

    • Undivided, TWLTL, divided

  • fID –access points T14.9

    • Driveways or roadways per mile on the right hand side - only include active intersections


  • Multilane highways2

    Multilane Highways

    • BFFS – use 60mph if no data available for rural and suburban multilane sites

      • Can estimate speed limit with BFFS

      • 7mph higher than spd limits 40 – 45mph

      • 5mph higher than spd limits 50 – 55mph


    Example

    Example

    • Old 6 lane freeway – 11’ lanes, barriers on right side 2’ from pavement edge, TRD = 3ramps/mile

      • FFS = 75.4- fLW - fLC – 3.22TRD^0.84

      • fLW – lane width adjustment T14.5

      • fLC – lateral clearance T14.6

        • 2’ on right side 6’ on left

        • Factor only takes right side into account


    Example1

    Example

    • Old 6 lane freeway – 11’ lanes, barriers on right side 2’ from pavement edge, TRD = 3 ramps/mile

      • FFS = 75.4- fLW - fLC – 3.22TRD^0.84

      • fLW – 1.9 mph T14.5

      • fLC – 1.6 mph T14.6

      • TRD = 3

    • FFS = 75.4 – 1.9 – 1.6 – 3.22*3^.84= 64.1


    Example2

    Example

    • 4 lane suburban multilane highway – 12’ lanes, barriers on right side 2’ from pavement edge, TWLTL, 30 access points/mile posted spd lmt = 50 mph

      • FFS = BFFS-fLW - fLC - fM – fA

      • fLW – 0.0 mph T14.5

      • fLC – 0.9 mph T14.7 total LC = 6+2 = 8’

      • fM –0.0 mph T 14.8

      • fID –7.5 mph T14.9

    • FFS = 55 – 0 – 0.9 – 0 – 7.5 = 46.6

    • 55 mph 50 + 5 mph for BFFS


    Heavy vehicle factor

    Heavy Vehicle Factor

    • Heavy Vehicle = any vehicle with more than 4 tires

      • Trucks and buses

        • Have similar characteristics

        • Based on a typical mix of trucks

        • 150#/hp

      • RVs

        • Privately owned, self contained or pulled

        • 75 -100 #/hp


    Passenger car equivalents

    Passenger Car Equivalents

    • # of cars displaced by the heavy vehicle

    • ET = PCE for trucks and buses

    • ER = PCE for RVs

    • Increases volume to account for HVs

    • EX: 1000 vehicles 10% trucks, 2% RV

      • ET = 2.5 ER = 2.0


    Freeways and multilane highways

    • 1000 * 0.1*2.5 = 250pce/hr

    • 1000*0.02*2 = 40 pce/hr

    • 1000*0.88 = 880 pce/hr

    • Total pce = 1170 pce/hr

      • Traffic stream acts like it has 1170 vph on it

      • fHV = vph/(pce/hr) always <= 1.0

      • fHV = 1000/1170 = 0.85


    Freeways and multilane highways

    • fHV = 1/(1+PT(ET – 1) +PR(ER – 1))

    • Extended Freeway & Multilane Sections

      • Long section = single section where no grade of 3% or greater is longer than 0.25 miles and if no grade of less than 3% is longer than 0.5 miles


    Terrain

    Terrain

    • Level terrain – short grades less than 2%

      • HVs can maintain same speed as cars

    • Rolling terrain - HV speed substantially below pc speeds but do not get to crawl speed for extended periods

    • Mountainous terrain – HV operate at crawl speed for extended periods or frequently

      • Rare

      • T14.11


    Specific grades

    Specific Grades

    • Any grade <3% longer than 0.5 miles or >3% and longer than 0.25 mile is a specific grade

    • T14.12, T14.13

    • Trucks on Downgrades T14.14

      • RVs same as level sections


    Composite grades

    Composite Grades

    • Series of grades

      • Want to get the equivalent uniform grade for pce

      • Average grade technique

        • Find total rise divide by total run

        • Good when all grades <4% and < 4000ft length

      • Composite grade technique

        • Use truck performance curves to determine equivalent length of grade


    Driver population factor

    Driver Population factor

    • Based on the number of drivers not familiar with the road.

      • Range from 1 – 0.85

      • Usually use 1 unless a field study has been done or it is a highly recreational area


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