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Ramps Weaving

Hmwk. Go thru Example Problems 15-1, 15-2, 15-3 and understandCh 15

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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

    51. Reasonableness of Lane Distribution 2. Ave Flow rate in the outer lanes cannot be more than 1.5 times the ave flow rate in lanes 1&2 For NO = 1 V12 = VF/1.75 For NO = 2 V12 = VF/2.50 For NO > 2 V12 = VF/(1.5*NO + 2) If both criterion violated, use values that satisfy both criteria

    52. Capacity Must check capacity of basic facility upstream and downstream of merge/diverge Use T 15.5 to compare values For merge areas – max flow occurs downstream of ramp vFO = vF+vR For diverge areas – max flow occurs upstream of ramp vF upstream of ramp

    53. Capacity For areas where lanes are added or dropped compare both vF and vFO to facility capacity For merge areas vR12 = v12 + vR are compared to max desirable flow For diverge areas v12 is compared All ramp flows must be compared to ramp capacities

    54. Density and LOS Merge areas DR = 5.475 + 0.0073vR + 0.0078v12 – 0.00627La Diverge areas DR = 4.252 + 0.0086v12 – 0.009La

    55. Speed 3 areas are checked Ramp Influence Area – 1500’ area encompassing ramp Outer Lanes - speed of outer lanes within ramp influence area All Lanes – speed of all lanes within the ramp influence area

    56. Speed T 15.6, 15.7 SR = space mean speed of vehicles in ramp influence area SO = space mean speed of vehicles in outer lanes within 1500’ length range of ramp influence area S = space mean speed of vehicles in all lanes within 1500’ length range of ramp influence area

    57. Speed MS = speed proportion factor for merge areas DS = speed proportion factor for diverge areas vOA = average demand flow in outer lanes = (vF-v12)/N0 pc/h/l NO = # of outer lanes

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