RAMPS & RAMP JUNCTIONS - Universiti Putra Malaysia：坡道&amp；匝道路口-马来西亚博特拉大学

RAMPS & RAMP JUNCTIONS - Universiti Putra Malaysia：坡道&；匝道路口-马来西亚博特拉大学 1 Department of Civil Engineering Faculty of Engineering University Putra Malaysia _____________________________________________________________________________ KAW4613 – Highway Capacity Analysis RAMPS & RAMP JUNCTIONS RAMP COMPONENTS 1. Ramp-Freeway Junction , permit high speed merge/diverge with minimum disruption to adjacent freeway traffic stream , operation depends on: - length & type of acceleration/deceleration lanes - Free flow speed of ramp in immediate vicinity of junction - sight distance 2. Ramp-Roadway , vary location to location , operation depends on: - nos. of lanes, length, design speed, grades, horizontal curvature , rarely a source of operational difficulties 3. Ramp-Street Junction , type permits uncontrolled merging/diverging movements to take place, or take the form of at-grade intersection OPERATIONAL CHARACTERISTICS HCM defines merge/diverge influence areas to include: , acceleration/deceleration lanes , lane 1 & 2 of freeway for distance 1,500 ft (458 metres) downstream of merge or upstream of diverge. Ramp junctions : Influence Areas & Critical Values V 1500-ft(458 m) R VV 12 R12V D , S V FRRFO Merge area (On-ramp) 1500-ft (458 m) V R V 12 D , S V RRFOV F Diverge area (Off-ramp) 2 METHODOLOGY Basic Structure of Methodology 3 MAJOR STEPS: 1. Determine V : 12(Must be known ~ major determinant of operating characteristics within ramp influence area) ~ flow entering Lanes 1 & 2 immediately upstream of merge influence area OR ~ flow at beginning of deceleration lane at an off-ramp 2. Determine Critical Capacity Values (CCV) Demand Flows Versus CCV Evaluated at 2 points: a) max. total flow departing from merge or diverge area. (V ~ on-ramps), (V ~ off-ramps) FOF b) max. total flow that can reasonably enter merge or diverge influence area. (V ~ on-ramps), (V ~ off-ramps) R1212 If Demand > either (a) or (b) ? Breakdown (LOS F) is likely. 3. Density (D) & LOS R For some situations, Average Speed (S) of vehicles may be predicted. RBefore any of these procedures are applied, all relevant freeway & ramp flows must be converted to equivalent pcph under ideal conditions for the peak 15-min. of hour. V veh/hr V = pcph PHF f f HVpwhere: V = max. 15-min flow rate in pcph under ideal conditions pcphV = hourly volume under prevailing conditions veh/hrPHF = peak hour factor f = adjustment factor for heavy vehicles HVf = adjustment factor for driver population p PREDICTION OF FLOW ENTERING LANES 1 & 2 (V) 12 Principal influences on lane distribution of freeway vehicles immediately upstream of merge or diverge: , V ~ total freeway flow approaching Fmerge/diverge area (pcph) , V ~ total ramp flow (pcph) R, L or L ~ total length of acceleration/deceleration lane (ft) AD , S ~ free-flow speed of ramp at point of merge/diverge (mph) FR Lane distribution may also be influenced by flows on adjacent upstream/downstream ramps: V ~ total flow on upstream adjacent ramp (pcph) VV ~ total flow on downstream adjacent ramp (pcph) DD ~ distance to adjacent upstream ramp (ft) VD ~ distance to adjacent downstream ramp (ft) D Significance influence on lane distribution depends on size of freeway, specific combination of upstream/downstream ramp (or both), and distances & flows involved. 3 General Model Structure , Model form for prediction of V immediately upstream of single-lane, left-hand on-ramps: 12V = V x P 12FFMP = proportion of freeway vehicles remaining in Lanes 1 & 2 immediately upstream of on-ramp. FM(behavioural choices of drivers selecting lanes) , Model for prediction of V immediately upstream of beginning of deceleration lane; single-lane, 12left-hand off-ramps: V = V + ( V - V ) P 12RFRFDP= proportion of through vehicles remaining in Lanes 1 & 2. FD (choice to be made by approaching freeway drivers not exiting at ramp) Specific Models Equations for P & P calibrated for different possible configurations (including width of freeway, upstream FMFD& downstream configurations): FIGURE 5-3 (Single-lane, left-hand ON-RAMPS) FIGURE 5-4 (Single-lane, left-hand OFF-RAMPS) Merge Equation : (ON-RAMPS) Eq. 1 : 4-lane freeways (trivial) Eq. 2 : 6-lane freeways (simple)*** Eq. 3 : 6-lane freeways (with effect of adjacent upstream off-ramp) Eq. 4 : 6-lane freeways (with effect of adjacent downstream off-ramp) Eq. 5 : 8-lane freeways *** Eq. 2 also used for 6-lane freeways (with effect of adjacent upstream on-ramp or downstream on-ramp) *** Eq. 2 used if variables of Eq. 3 or Eq. 4 is outside the limits. Diverge Equation : (OFF-RAMPS) Eq. 6 : 4-lane freeways (trivial) Eq. 7 : 6-lane freeways (simple)*** Eq. 8 : 6-lane freeways (with effect of adjacent upstream on-ramp) Eq. 9 : 6-lane freeways (with effect of adjacent downstream off-ramp) Eq. 10 : 8-lane freeways *** Eq. 7 also used for 6-lane freeways (with effect of adjacent upstream off-ramp or downstream on-ramp) *** Eq. 7 used if variables of Eq. 8 or Eq. 9 is outside the limits. CAPACITY VALUES Merge areas (TABLE 5-1) Controlled by : EITHER a) total flow leaving merge area on downstream freeway, (V ) OR FOb) max. flow entering merge influence area (V), where : V = V + V R12R12R12 If Demand at either points > Capacity values? LOS F , Analysis ENDS. Otherwise? Estimate Density , LOS Diverge areas (TABLE 5-1) Check 3 Capacity values : a) total flow that may leave diverge area (V), OR Fb) max. flow that may enter Lanes 1 & 2 immediately before deceleration lane (V), OR 12c) capacity of each of the exiting legs of the freeway, (TABLE 5-6) LEVEL OF SERVICE , Prediction of Density, D ( TABLE 5-3 ) ~ establish LOS R , Prediction of Speed, S ( TABLE 5-4 ) ~ never use to establish LOS R 4 PROCEDURES FOR APPLICATION Single-lane on- & off-ramps STEP 1 : Specify geometry & demand volumes (vph) STEP 2 : Convert all demand vol. (vph) into 15-min peak flow rates (pcph) under ideal conditions. STEP 3 : Estimate V ~ FIG.5-3 (merge area), FIG.5-4 (diverge area) 12 STEP 4 : Find checkpoint flow rates: Merge areas : V = V + V FOFR : V = V + V R12R12 Diverge areas : V = V + V FFOR : V 12 : V ~ (TABLE 5-6) R Compare with Capacity values in TABLE 5-1 STEP 5 : If Step 4 = LOS F, then ignore Step 5. Otherwise? Determine D (TABLE 5-3) , LOS (TABLE 5-2). May estimate S (TABLE 5-4) RR SPECIAL APPLICATIONS Two-Lane On-Ramp ( FIG. 5-6 ) Computing V for 2-lane on-ramps: V = V (P) 1212FFM Replace formula for P in FIG.5-3 by: FM, 4-lane freeways, P = 1.0000 FM , 6-lane freeways, P = 0.5550 FM, 8-lane freeways, P = 0.2093 FM Computing Density: Use Equation in TABLE 5-3, but L replaced by L. Where : L = 2L + L AAeffAeffA1 A2 Computing Capacity Values : TABLE 5-1 ~ No Change Two-Lane Off-Ramp ( FIG. 5-7a , FIG. 5-7b ) 2 general types of geometry: Type 1 : (FIG. 5-7a) ~ 2 deceleration lanes successively introduced, Type 2 : (FIG. 5-7b) ~ Single deceleration lane used. Computing V for 2-lane off-ramps: V = V + (V – V)P) 1212RFRFD Replace formula for P in FIG. 5-4 by: FD, 4-lane freeways, P = 1.000 FD , 6-lane freeways, P = 0.450 FD, 8-lane freeways, P = 0.260 FD Computing Density: Type 1 ? Use Equation in TABLE 5-3, but L replaced by L. Where, L = 2L + L DDeffDeffD1 D2Type 2? Use Equation in TABLE 5-3 without modification Computing Capacity Values : TABLE 5-1 ~ No modification 5 Right-Hand Ramps No direct method available. Apply rational modifications to Left-Hand Ramps method ~ reasonable result Compute V using standard procedures, then : 12 , RHR ~ 4-lane freeways, V = V 1212 , RHR (On) ~ 6-lane freeways, V = 1.12 V 2312 , RHR (Off) ~ 6-lane freeways, V = 1.05 V 2312 , RHR (On) ~ 8-lane freeways, V = 1.20 V 3412 , RHR (Off) ~ 8-lane freeways, V = 1.15 V 3412 Compute for Density : the same except Replace V with V or V as appropriate 122334