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Ramps & Weaving

Ramps & Weaving. Hmwk. Go thru Example Problems 15-1, 15-2, 15-3 and understand Ch 15 # 1, 2, 4 can use HCS+. Merging & Diverging movements Cause turbulence in the traffic stream More lane changing, changes in speed, lower average speeds F 15-1 Paths of Ramps and weaves. Merging

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Ramps & Weaving

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  1. Ramps & Weaving

  2. Hmwk • Go thru Example Problems 15-1, 15-2, 15-3 and understand • Ch 15 # 1, 2, 4 can use HCS+

  3. Merging & Diverging movements • Cause turbulence in the traffic stream • More lane changing, changes in speed, lower average speeds • F 15-1 Paths of Ramps and weaves

  4. Merging • Occurs when 2 separate traffic streams form a single stream (not lane) • Can occur at on ramp, 2 facilities joining • Merging vehicles change lane to enter traffic stream • Non merging traffic changes lanes to avoid merging traffic

  5. Diverging • One stream separates into 2 • Off ramps and major highway splits • Diverging vehicles must align themselves in proper lane • Non diverging vehicles must change lanes to avoid diverging vehicles

  6. Weaving • Occurs when merge and diverge are spaced closely to each other • 2500’ is max spacing for weave • But must have a continuous auxiliary lane connecting the two ramps

  7. LOS Criteria • Measure of effectiveness = density • T15.1 • For weaving • Density is an average of all vehicles across all lanes between exit & entry point • Merge & diverge influence areas F15.2 • Density is 2 right hand lanes + auxiliary lane • Can have overlap • Use worst case for LOS

  8. Converting Demand Volumes • Must convert all component volumes to a demand volume • vi = Vi/(PHF*fHV*fp) • vi = demand volume under base conditions • Vi= volume under prevailing conditions (vol found with count)

  9. Analysis of Weaving Areas • Flows in a weaving area • F15.3 do on board • vo1 = larger outer flow – non weaving • vo2 = smaller outer flow – non weaving • vw1 = larger weaving flow • vw2 = smaller weaving flow • All in pc/h base conditions • By convention traffic flow is L->R

  10. Analysis of Weaving Areas • vw = total weaving flow = vw1 + vw2 • vnw = total non weaving flow = vo1 + vo2 • v= total flow = vw + vnw • VR volume ratio = vw /v • R = weaving ratio vw2 / vw

  11. Geometric Variables • Lane configuration • How entry and exit lanes connect • 4 configurations • F15.4 • Ramp weave F15.4(a) • 1 lane on ramp followed by 1 lane off ramp connected with auxiliary lane • Every weaving vehicle must make a lane change • Ramps have lower speed than highway • All weaving vehicles make 1 lane change

  12. Geometric Variables • All weaves must take place within weave area • Major weave – F 15.4(b) • Lane changing pattern similar • 3 of 4 entry lanes have 2 lanes • Vehicles accel or decel thru weave area • Ramps and weaves on 1 side of road

  13. Geometric Variables • 2 sided ramp weave F 15-4(c) • Single lane on ramp followed by 1 lane off ramp on opposite side of road • Vehicles must traverse all lanes • Vehicles occupy all lanes for a period of time

  14. Major Weave – F 15-4(d) • 3 of 4 entry/exit lanes have 2 lanes • Ramps on opposite sides of freeway • Vehicles must traverse all lanes • Vehicles occupy all lanes for a period of time

  15. One sided weaves • Fig 15-5 shows critical parameters • LCRF =minimum # of lane changes ramp ->facility vehicle must make • Usually 0, 1 • LCFR =minimum # of lane changes facility -> ramp vehicle must make • Usually 0, 1 • Nwv =# of lanes from which a maneuver may be completed with 1 or no lane changes • Nwv =either 2 or 3 • What are values for Fig 15-5?

  16. One sided weaves • Nwv =# of lanes from which a maneuver may be completed with 1 or no lane changes • Nwv =either 2 or 3 • What are values for Fig 15-5?

  17. Two sided weaves • LCRF , LCFR =>not weaving flows • LCRR = minimum # of lane changes ramp ->ramp vehicle must make • Nwv =0 by definition • What are values for Fig 15-5?

  18. Length of Weaving Area • Length is critical in determining intensity of lane changing • Fig 15.6 shows 2 ways to measure length • LS is used in calculations

  19. Width of Weaving Area • Measured as # of lanes available for all flows (N) • Width of weave has impact of total number of lane changes that drivers can choose to make • Proportional use of lanes by weaving and non-weaving vehicles • Normal conditions – vehicles compete for space and operations across all lanes reach equilibrium • All drivers experiencing similar conditions

  20. In weaving areas • Always some segregation of weaving and non-weaving flows • Non-weaving drivers stay to the outside lanes to avoid turbulence • Weaving drivers need to occupy lanes for maneuver • Non-weaving and weaving vehicles do share lanes • Will share in a manner that provides them with similar operating quality

  21. Flow Chart • F 15.7 • Variables for 1 sided weave • F 15.8 • Variables for 1 sided weave • F 15.9

  22. Configuration characteristics • Nwv = • LCMin = minimum rate at which weaving vehicles must change lanes to successfully complete all weaving maneuvers in lane changes per hour • LCMin = (LCFR * vFR) + (LCRF * vRF) – 1 sided • LCMin = LCRR * vRR - 2 sided

  23. Max Weaving Length • 1. length at which weaving turbulence no longer impacts operations in the segment • 2. length at which weaving turbulence no longer impacts capacity of the segment • Use this definition • LMax = [5728*(1+VR)1.6] – (1566*NWV) • Weaving length increases as VR increases

  24. Max Weaving Length • If LMax => LS use weaving methodology • If LMax < LS use merge and diverge methodology

  25. Capacity of Weaving Segment • Must have stable flow • NOT LOS F • 2 situations where breakdown occurs • 1 – demand flow > total capacity of segment • ~43 pc/mi/ln in the weaving segment • 2 – Total weaving flow rate > capacity of segment to handle weaving flows • Maximum values • 2400 pc/hr NWV = 2 lanes • 3500 pc/hr NWV = 3 lanes

  26. Capacity based on Breakdown Density • cIWL = cIFL – [438.2*(1+VR)1.6] + 0.0765LS +119.8NWV • cIFL = capacity per lane of basic freeway segment with same FFS as weaving section • Table 15.2 • cIWL = capacity per lane of weaving section under ideal conditions

  27. Capacity based on Breakdown Density • cW1 = cIWL*N*fHV*fp • cW1 = capacity of weaving section based on breakdown density

  28. Capacity based on Maximum Weaving Flow Rates • # of weaving vehicles hits capacity before the density of the entire segment reaches 43 pc/mi/ln • Weaving turbulence can cause a breakdown causing on-ramp vehicles to queue or off ramp queues on the freeway • cIW = 2400/VR for NWV =2 or • cIW = 3500/VR for NWV =3 • cIW = capacity of weaving section under ideal conditions

  29. Capacity based on Maximum Weaving Flow Rates • cW2 = cIW*fHV*fp • capacity of weaving segment based on maximum weaving flow

  30. Capacity of Weaving Segment • Capacity is smaller value • cW = min(cW1, cW2) • Find v/c • v/c = vfHVfp/ cW • If v/c >= 1 then LOS F -STOP

  31. Total Lane Changing Rate within the Weaving Segment • 3 types of lane changing maneuvers within Weaving Segment • 1. Required lane changes by weaving vehicles • Absolute minimum lane changing rate that can exist in the weaving segment for the defined demands. Must be made within the weaving segment. • Weaving segment length = • LCMin = (LCFR * vFR) + (LCRF * vRF) – 1 sided • LCMin = LCRR * vRR - 2 sided

  32. Total Lane Changing Rate within the Weaving Segment • 2. Optional lane changes made by weaving vehicles that choose to enter segment on a lane that is not closest to their desired destination or leave segment that is not closest to their entry leg. Requires additional lane change within the weaving segment • Increases turbulence • Use reference 15

  33. Total Lane Changing Rate within the Weaving Segment • 3. Optional lane change made by non-weaving vehicles. • Non-weaving vehicles never have to change lanes within a weaving segment • May choose to make lane change to avoid turbulence • Use reference 15

  34. Total Lane Changing Rate for Weaving Vehicles • LCW = LCMin + 0.39*[LS-300)0.5*N2*(1 +ID)0.8 • LCW = Total lane changing rate for weaving vehicles within weaving segment lc/h • ID = interchange density interchanges/mi • Weave segment counts as 1, count # within 3 miles of center of weave • Multilane highways use major access points • LS-300 ->for segments shorter than 300’ weaving vehicles do not make optional lane changes (cannot be negative)

  35. Total Lane Changing Rate for Non-Weaving Vehicles • LCNW1 = 0.206vNW + 0.542LS-192.6N • LCNW2 = 2135 + 0.223*(vNW-2000) • LCNW1 = 1st estimate of NW lane changes • LCNW2 = 2nd estimate of NW lane changes • 1st equation covers most situations • As NW flow increases -> NW lane changing increases • As Length increases ->NW lane changing increases • As N increases ->NW lane changing decreases

  36. Total Lane Changing Rate for Non-Weaving Vehicles • 2 equations are very discontinuous so need an index to determine use • INW = (LS*ID*vNW)/10000 • Explains when the second equation is used • Applies to cases with long lengths, high ID’s and/or high NW flows occur

  37. Total Lane Changing Rate for Non-Weaving Vehicles • If INW <= 1300 • LCNW = LCNW1 • If INW => 1950 • LCNW = LCNW2 • If 1300<= INW <= 1950 • LCNW = LCNW1 + (LCNW2 + LCNW1)*((INW-1300)/650)

  38. Total Lane Changing Rate in Weaving Segment • LCALL = LCW + LCNW

  39. Average Speed of Vehicles • Find speed for both weaving and non-weaving vehicles • Affected by different factors • Speed is used to find Density which is used to determine LOS

  40. Average Speed of Weaving Vehicles • SW = SMIN +(SMAX – SMIN)/(1+W) • SW = Average speed of weaving vehicles • SMIN = min ave spd of weaving veh in weaving segment • SMAX = Max ave spd of weaving veh in weaving segment • W = weaving intensity factor • W = 0.226*(LCALL/LS)0.789

  41. Average Speed of Weaving Vehicles • SW = 15 +(FFS – 15)/(1+W) • Where the minimum speed = 15mph • Maximum speed = FFS

  42. Average Speed of Non-Weaving Vehicles • SNW = FFS – 0.0072LCMIN – 0.0048v/N • LCMIN shows measure of weaving turbulence

  43. Average Speed of All Vehicles • S = (vW + vNW)/((vW/SW) + (vNW/SNW)) • Density • D = (v/N)/S • With Density, LOS can be determined

  44. Merge & Diverge • Basic Characteristics • Analysis focuses on right 2 lanes – need to know lane distribution of the freeway upstream of the ramp • Fig 15.10 • Variables pg 334 • La or Ld – acceleration or deceleration ramp length Fig 15.11 • RFFS – ramp FFS

  45. Analysis of Merge/Diverge Areas • F 15.12 – flowchart

  46. Analysis of Merge/Diverge Areas • Merge Areas • Find flow remaining in lanes 1&2 upstream of junction • v12 = vF * PFM • PFM = proportion of approaching vehicles remaining in lanes 1&2 immediately upstream of junction (decimal) • Varies with # of lanes on facility – T 15.3

  47. Ramp Analysis • Is ramp isolated? • Need to know distance apart and where equivalence distance is located • For upstream off ramps • LEQ = 0.214(vF+vR)+0.444La+52.32RFFS – 2403 • If LEQ >=Lup = isolated ramp • For downstream off ramps • LEQ = vd/(0.1096+0.000107La) • Vd= demand flow rate on downstream ramp pc/h • If Ldn >=LEQ = isolated ramp

  48. Diverge • Need to account for all diverging traffic being in lanes 1&2 • v12 = vR + (vF - vR )PFD • PFD = proportion of approaching vehicles remaining in lanes 1&2 immediately upstream of junction (decimal) • Varies with # of lanes on facility – T 13.7

  49. Diverge • Need to determine if ramp is isolated • For adjacent upstream on-ramps • LEQ = vu/(0.071+0.000023vF-0.000023vR) • vu = demand flow rate on upstream on ramp • If Lup >= LEQ = isolated ramp • For adjacent downstream off ramp • LEQ = vd/(1.15-0.000032vF-0.000369vR) • If Ldn >= LEQ = isolated ramp

  50. Reasonableness of Lane Distribution • Does lane distribution make sense? • 1. Ave flow rate in outer lanes may not exceed 2700 pc/ln/hr • If exceeded then • V12 = VF – 2700NO

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