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 –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

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 Pure uninterrupted flow –Cars enter and exit via ramps –No at grade intersections, driveways etc Based on number of lanes

Multilane Highways Only uninterrupted flow if signals at least 2 miles apart Classified by lanes and median type F 14.1

LOS MOE is density – pc/ln/mi Capacity = 45pc/ln/mi –Freeways –multilane hwys => pc/ln/mi –F 14.2, 14.3, T 14.1 LOS pg

Freeway Analysis F14.2 & 14.3 Operational Analysis How is the existing facility operating v p = V/(PHF*N* f HV * f p ) = pc/hr/ln v p is the demand flow rate under ideal conditions With v p can find FFS from curves F 14.2 f p = user population If V = 4600vph, PHF = 0.90, N =3, f HV =0.87, f p = 1 What is LOS v= 1958pc/h/ln => LOS =? F 14.2 &3

Service Flow Rate & Service Vol Analysis SF i = MSF i *N*f HV *f p –Can find service flow for each LOS i Use Tables 14.3 or 14.4 to get MSF

Design Analysis –Used to determine # of lanes needed for freeway –To determine the number of lanes –N = DDHV/(PHF*MSF*f HV *f p ) –Iterative process –Number of lanes depends on design speed –Design speed depends on # of lanes

Free Flow Speed - Freeways Free Flow Speed –Found when volume < 1000vph/l –FFS = BFFS-f LW - f LC – 3.22TRD^0.84 –f LW – lane width adjustment T14.5 –f LC – 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 Highways –FFS = BFFS-f LW - f LC - f M – f A –f LW – lane width adjustment T14.5 –f LC – lateral clearance T14.7 –Greatest LC = 6 feet on both sides –Undivided Hwys – no median side clearance – taken into account with f M – assume 6’ clearance –TWLTL – assume 6’ clearance –Divided hwy – based on median, dist to opposing traffic, periodic objects(light poles) never more than 6’ –f M –median type T 14.8 Undivided, TWLTL, divided –f ID – access points T14.9 Driveways or roadways per mile on the right hand side - only include active intersections

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 Old 6 lane freeway – 11’ lanes, barriers on right side 2’ from pavement edge, TRD = 3ramps/mile –FFS = f LW - f LC – 3.22TRD^0.84 –f LW – lane width adjustment T14.5 –f LC – lateral clearance T14.6 2’ on right side 6’ on left Factor only takes right side into account

Example Old 6 lane freeway – 11’ lanes, barriers on right side 2’ from pavement edge, TRD = 3 ramps/mile –FFS = f LW - f LC – 3.22TRD^0.84 –f LW – 1.9 mph T14.5 –f LC – 1.6 mph T14.6 –TRD = 3 FFS = 75.4 – 1.9 – 1.6 – 3.22*3^.84= 64.1

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-f LW - f LC - f M – f A –f LW – 0.0 mph T14.5 –f LC – 0.9 mph T14.7 total LC = 6+2 = 8’ –f M –0.0 mph T 14.8 –f ID – 7.5 mph T14.9 FFS = 55 – 0 – 0.9 – 0 – 7.5 = mph mph for BFFS

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 #/hp

Passenger Car Equivalents # of cars displaced by the heavy vehicle E T = PCE for trucks and buses E R = PCE for RVs Increases volume to account for HVs EX: 1000 vehicles 10% trucks, 2% RV –E T = 2.5 E R = 2.0

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 –f HV = vph/(pce/hr) always <= 1.0 –f HV = 1000/1170 = 0.85

f HV = 1/(1+P T (E T – 1) +P R (E R – 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 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 Any grade 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 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 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