Highway Capacity Manual 2010

Transcription

1 RR = minimum number of lane change that mut be made by one ramp-toramp ehicle to execute the deired maneuer uccefully. MIN for two-ided weaing egment i gien by Equation 12-3: MIN RR For two-ided weaing egment, the alue of N L i alway 0 by definition. Step 4: Determine Maximum eaing Length The concept of maximum length of a weaing egment i critical to the methodology. Strictly defined, maximum length i the length at which weaing turbulence no longer ha an impact on operation within the egment, or alternatiely, on the capacity of the weaing egment. Unfortunately, depending on the elected definition, thee meaure can be quite different. eaing turbulence will hae an impact on operation (i.e., weaing and nonweaing ehicle peed) for ditance far in exce of thoe defined by when the capacity of the egment i no longer affected by weaing. Thi methodology ue the econd definition (baed on the equialence of capacity). If the operational definition were ued, the methodology would produce capacity etimate in exce of thoe for a imilar baic freeway egment, which i illogical. The maximum length of a weaing egment (in feet) i computed from Equation 12-4: RR 1.6 5,7281 VR 1, L 566 MAX N L where L MAX i the maximum weaing egment length (uing the hort length definition) and other ariable are a preiouly defined. A VR increae, it i expected that the influence of weaing turbulence would extend for longer ditance. All alue of N L are either 0 (two-ided weaing egment) or 2 or 3 (one-ided weaing egment). Haing more lane from which eay weaing lane change can be made reduce turbulence, which in turn reduce the ditance oer which uch turbulence affect egment capacity. Exhibit 12-9 illutrate the enitiity of maximum length to both VR and N L. A expected, VR ha a ignificant impact on maximum length, a doe the configuration, a indicated by N L. hile the maximum length hown can compute to ery high number, the highet reult are well outide the calibration range of the equation (limited to about 2,800 ft), and many of the ituation are improbable. Value of VR on egment with N L = 2.0 lane rarely rie aboe the range of 0.40 to hile alue of VR aboe 0.70 are technically feaible on egment with N L = 3.0 lane, they are rare. hile the extreme alue in Exhibit 12-9 are not practical, it i clear that the maximum length of weaing egment can rie to 6,000 ft or more. Furthermore, the maximum length can ary oer time, a VR i not a contant throughout eery demand period of the day. Equation 12-3 The maximum length of a weaing egment, L MAX, i baed on the ditance beyond which additional length doe not add to capacity. Equation 12-4 Chapter 12/Freeway eaing Segment Page Methodology

2 Exhibit 12-9 Variation of eaing Length Veru Volume Ratio and Number of eaing Lane (ft) Maximum eaing Length (ft) VR N L = 2 N L = ,540 1, ,536 2, ,584 4, ,681 5, ,826 6, ,019 7, ,256 8, ,538 9,972 If the length of the egment i greater than L MAX, it hould be analyzed a eparate merge and dierge ramp junction by uing the methodology in Chapter 13. Any portion falling outide the influence of the merge and dierge egment i treated a a baic freeway egment. A weaing egment capacity i controlled by either (a) the aerage ehicle denity reaching 43 pc/mi/ln or (b) the weaing demand flow rate exceeding a alue that depend on the number of weaing lane. The alue of L MAX i ued to determine whether continued analyi of the configuration a a weaing egment i jutified: If L S < L MAX, continue to Step 5; or If L S L MAX, analyze the merge and dierge junction a eparate egment by uing the methodology in Chapter 13. If the egment i too long to be conidered a weaing egment, then the merge and dierge area are treated eparately. Any ditance between the two falling outide the influence area of the merge and dierge egment would be conidered to be a baic freeway egment and would be analyzed accordingly. Step 5: Determine eaing Segment Capacity The capacity of a weaing egment i controlled by one of two condition: Breakdown of a weaing egment i expected to occur when the aerage denity of all ehicle in the egment reache 43 pc/mi/ln; or Breakdown of a weaing egment i expected to occur when the total weaing demand flow rate exceed o o 2,400 pc/h for cae in which N L = 2 lane, or 3,500 pc/h for cae in which N L = 3 lane. The firt criterion i baed on the criteria lited in Chapter 11, Baic Freeway Segment, which tate that freeway breakdown occur at a denity of 45 pc/mi/ln. Gien the additional turbulence in a weaing egment, breakdown i expected to occur at lightly lower denitie. The econd criterion recognize that there i a practical limit to how many ehicle can actually cro each other path without cauing eriou operational failure. The exitence of a third lane from which weaing maneuer can be made with two or fewer lane change in effect pread the impact of turbulence acro egment lane and allow for higher weaing flow. For two-ided weaing egment (N L = 0 lane), no limiting alue on weaing flow rate i propoed. The analyi of two-ided weaing egment i approximate with thi methodology, and a denity ufficient to caue a breakdown i generally reached at relatiely low weaing flow rate. eaing Segment Capacity Determined by Denity The capacity of a weaing egment, baed on reaching a denity of 43 pc/mi/ln, i etimated by uing Equation 12-5: Methodology Page Chapter 12/Freeway eaing Segment

3 Step 8: Determine LOS The LOS in a weaing egment, a in all freeway analyi, i related to the denity in the egment. Exhibit proide LOS criteria for weaing egment on freeway, collector ditributor (C-D) roadway, and multilane highway. Thi methodology wa deeloped for freeway weaing egment, although an iolated C-D roadway wa included in it deelopment. The methodology may be applied to weaing egment on uninterrupted egment of multilane urface facilitie, although it ue in uch cae i approximate. Denity (pc/mi/ln) eaing Segment on Multilane LOS Freeway eaing Segment Highway or C-D Roadway A B >10 20 >12 24 C >20 28 >24 32 D >28 35 >32 36 E >35 43 >36 40 F >43, or demand exceed capacity >40, or demand exceed capacity LOS can be determined for weaing egment on freeway, multilane highway, and C-D roadway. Exhibit LOS for eaing Segment The boundary between table and untable flow the boundary between leel of erice E and F occur when the demand flow rate exceed the capacity of the egment, a decribed in Step 5. The threhold denitie for other leel of erice were et relatie to the criteria for baic freeway egment (or multilane highway). In general, denity threhold in weaing egment are omewhat higher than thoe for imilar baic freeway egment (or multilane highway). It i belieed that drier will tolerate higher denitie in an area where lane-changing turbulence i expected than on baic egment. To apply denity criteria, the aerage peed of all ehicle, computed in Step 7, mut be conerted to denity by uing Equation D where D i denity in paenger car per mile per lane and all other ariable are a preiouly defined. N S Equation SPECIAL CASES Multiple eaing Segment hen a erie of cloely paced merge and dierge area create oerlapping weaing moement (between different merge dierge pair) that hare the ame egment of a roadway, a multiple weaing egment i created. In earlier edition of the HCM, a pecific application of the weaing methodology for twoegment multiple weaing egment wa included. hile it wa a logical extenion of the methodology, it did not addre cae in which three or more et of weaing moement oerlapped, nor wa it well-upported by field data. Chapter 12/Freeway eaing Segment Page Methodology

4 Multiple weaing egment hould be analyzed a eparate merge, dierge, and imple weaing egment, a appropriate. The methodology applie approximately to C-D roadway, but it ue may produce an oerly negatie iew of operation. Multilane highway weaing egment may be analyzed with thi methodology, except in the icinity of ignalized interection. No generally accepted analyi methodologie currently exit for arterial weaing moement. Multiple weaing egment hould be egregated into eparate merge, dierge, and imple weaing egment, with each egment appropriately analyzed by uing thi chapter methodology or that of Chapter 13, Freeway Merge and Dierge Segment. Chapter 11, Baic Freeway Segment, contain information relatie to the proce of identifying appropriate egment for analyi. C-D Roadway A common deign practice often reult in weaing moement that occur on C-D roadway that are part of a freeway interchange. The methodology of thi chapter may be approximately applied to uch egment. The FFS ued mut be appropriate to the C-D roadway. It would hae to be meaured on an exiting or imilar C-D roadway, a the predictie methodology of FFS gien in Chapter 11 doe not apply to uch roadway. It i le clear that the LOS criteria of Exhibit are appropriate. Many C-D roadway operate at lower peed and higher denitie than on baic egment, and the criteria of Exhibit may produce an inappropriately negatie iew of operation on a C-D roadway. If the meaured FFS of a C-D roadway i high (greater than or equal to 50 mi/h), the reult of analyi can be expected to be reaonably accurate. At lower FFS alue, reult would be more approximate. Multilane Highway eaing egment may occur on urface multilane highway. A long a uch egment are a ufficient ditance away from ignalized interection o that platoon moement are not an iue the methodology of thi chapter may be approximately applied. Arterial eaing The methodology of thi chapter doe not apply to weaing egment on arterial. Arterial weaing i trongly affected by the proximity and timing of ignal along the arterial. At the preent time, there are no generally accepted analytic methodologie for analyzing weaing moement on arterial. Methodology Page Chapter 12/Freeway eaing Segment

5 Step 5: Determine eaing Segment Capacity The capacity of a two-ided weaing egment can only be etimated when a denity of 43 pc/h/ln i reached. Thi etimation i made by uing Equation 12-5 and Equation 12-6: c c c IL IL c c 8 IL IFL 2,300 N f HV VR L 119. L f p c IL 1,867 pc/h/ln 1, ,573 eh/h 4,415 eh/h Becaue the capacity of the egment exceed the demand olume (in ehicle per hour), LOS F i not expected, and the analyi may be continued. Step 6: Determine Lane-Changing Rate Equation through Equation are ued to etimate the lanechanging rate of weaing and nonweaing ehicle in the weaing egment. In turn, thee will be ued to etimate weaing and nonweaing ehicle peed. eaing Vehicle Lane-Changing Rate MIN L 300 N 1 ID lc/h Nonweaing Vehicle Lane-Changing Rate LS ID ,017 I 753 1,300 10,000 10, L N , lc/h Total Lane-Changing Rate ALL ,823 lc/h Step 7: Determine Aerage Speed of eaing and Nonweaing Vehicle The aerage peed of weaing and nonweaing ehicle are computed from Equation through Equation 12-20: Then L S ALL S , FFS mi/h Chapter 12/Freeway eaing Segment Page Example Problem

6 and S S FFS MIN 0048 N , mi/h Equation i now ued to compute the aerage peed of all ehicle in the egment: S S Step 8: Determine LOS S 5, mi/h 5, The aerage denity in thi two-ided weaing egment i etimated by uing Equation 12-22: N D S 5, pc/mi/ln From Exhibit 12-10, thi denity i clearly in LOS E. It i not far from the 43 pc/h/ln that would likely caue a breakdown. Dicuion Thi two-ided weaing egment operate at LOS E, not far from the LOS E/F boundary. The /c ratio i 4,150/4,573 = The major problem i that 300 eh/h croing the freeway from ramp to ramp create a great deal of turbulence in the traffic tream and limit capacity. Two-ided weaing egment do not operate well with uch large number of ramp-to-ramp ehicle. If thi were a baic freeway egment, the per lane flow rate of 5,408/3 = 1,803 pc/h/ln would not be conidered exceie and would be well within a baic freeway egment capacity of 2,300 pc/h/ln. EXAMPLE PROBLEM 4: DESIGN OF A MAJOR EAVING SEGMENT FOR A DESIRED LOS The eaing Segment A weaing egment i to be deigned between two major junction in which two urban freeway join and then eparate a hown in Exhibit Entry and exit leg hae the number of lane hown. The maximum length of the weaing egment i 1,000 ft, baed on the location of the junction. The FFS of all entry and exit leg i 75 mi/h. All demand are hown a flow rate under equialent ideal condition. Example Problem Page Chapter 12/Freeway eaing Segment

7 paing lane or multilane highway), calculate the directional demand flow rate of motorized traffic in the outide lane with Equation 15-24: where OL V PHF N OL = directional demand flow rate in the outide lane (eh/h), V = hourly directional olume (eh/h), PHF = peak hour factor, and N = number of directional lane (=1 for two-lane highway). Step 3: Calculate the Effectie idth The effectie width of the outide through lane depend on both the actual width of the outide through lane and the houlder width, ince cyclit will be able to trael in the houlder where one i proided. Moreoer, triped houlder of 4 ft or greater proide more ecurity to cyclit by giing cyclit a dedicated place to ride outide of the motorized ehicle traelway. Thu, an 11-ft lane and adjacent 5-ft paed houlder reult in a larger effectie width for cyclit than a 16-ft lane with no adjacent houlder. Parking occaionally exit along two-lane highway, particularly in deeloped area (Cla III highway) and near entrance to recreational area (Cla II and Cla III highway) where a fee i charged for off-highway parking or where the off-highway parking i inadequate for the parking demand. Onhighway parking reduce the effectie width, becaue parked ehicle take up houlder pace and bicyclit leae ome hy ditance between themele and the parked car. Equation through Equation are ued to calculate the effectie width, e, on the bai of the paed houlder width,, and the hourly directional olume per lane, V: If i greater than or equal to 8 ft: e (% OHP 10 ft) If i greater than or equal to 4 ft and le than 8 ft: If i le than 4 ft: with, if V i greater than 160 eh/h/ln: Otherwie, where e 2 (% OHP(2 ft )) e (% OHP(2 ft )) OL ( V ) = effectie width a a function of traffic olume (ft), OL Equation Equation Equation Equation Equation Equation Chapter 15/Two-Lane Highway Page Methodology

8 OL = outide lane width (ft), = paed houlder width (ft), V = hourly directional olume per lane (eh/h/ln), e = aerage effectie width of the outide through lane (ft), and %OHP = percentage of egment with occupied on-highway parking (decimal). Equation Step 4: Calculate the Effectie Speed Factor The effect of motor ehicle peed on bicycle quality of erice i primarily related to the differential between motor ehicle and bicycle trael peed. For intance, a typical cyclit may trael in the range of 15 mi/h. An increae in motor ehicle peed from 20 to 25 mi/h i more readily perceied than a peed increae from 60 to 65 mi/h, ince the peed differential increae by 100% in the firt intance compared with only 11% in the latter. Equation how the calculation of the effectie peed factor that account for thi diminihing effect. S ln( S 20) t p where S t = effectie peed factor, and S p = poted peed limit (mi/h). Equation Step 5: Determine the LOS ith the reult of Step 1 4, the bicycle LOS core can be calculated from Equation 15-31: where BLOS ln( 7.066(1/ P) 2 OL BLOS = bicycle leel of erice core; ) S ( HV ) 0.005( ) e 2 t OL = directional demand flow rate in the outide lane (eh/h); HV = percentage of heay ehicle (decimal); if V < 200 eh/h, then HV hould be limited to a maximum of 50%; P = FHA 5-point paement urface condition rating; and e = aerage effectie width of the outide through lane (ft). Finally, the BLOS core alue i ued in Exhibit 15-4 to determine the bicycle LOS for the egment. 2 Methodology Page Chapter 15/Two-Lane Highway