Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual (2016) / Chapter Skim
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From page 39... ...
P A R T 2 Medium-Level Analysis Methods The sections in Part 2 of the Guide describe medium-level analysis methods that work best when evaluating a single freeway, highway, or urban street facility and its component interchanges, segments, and intersections. The sections are organized according to the system elements (e.g., freeways, signalized intersections)
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43 H Freeway Analyses 1.
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44 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual 3. Analysis Methods Overview Freeway performance can be directly measured in the field or estimated in great detail using microsimulation.
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H. Freeway Analyses 45 can also be used to quickly compare improvement alternatives according to the capacity they provide.
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46 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Estimating Freeway Service Volumes The approximate maximum AADT (two-way) that can be accommodated by a freeway at a given LOS can be estimated from Exhibit 19.
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H. Freeway Analyses 47 5.
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48 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual on-ramp and an off-ramp may be composed of three HCM segments: a merge segment, a basic or weave segment, and a diverge segment. Defining Sections for the Simplified Method Input variables are characterized as global or section inputs.
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H. Freeway Analyses 49 Estimating Inputs This subsection describes procedures for estimating the free-flow speed, the section type, and the section capacities.
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50 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual where Ci = capacity of section i (veh/h/ln) , SFFS = free-flow speed (mph)
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H. Freeway Analyses 51 where qi,t = in- or outflow for section i during analysis period t (veh/h)
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52 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual onto the freeway, affecting mainline operations. The complexity of such a situation goes beyond typical planning analysis and may require microsimulation to adequately assess the severity of the problem and its impacts on freeway mainline operations.
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H. Freeway Analyses 53 rate is approximated assuming uniform arrivals and departures at a freeway bottleneck.
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54 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual basic section speed. In the absence of local data, a value of 0.95 is recommended for CAFmerge regardless of the merge configuration.
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H. Freeway Analyses 55 where D = mixed vehicle density (veh/mi/ln)
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56 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual ( ) = −max , 0 Equation 31, , , QL d c D i t i t i i i where QLi,t = queue length in segment i at time t (veh)
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H. Freeway Analyses 57 HCM Method Using Defaults The HCM method for estimating travel time reliability is described in HCM Chapter 11.
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58 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Values of X greater than 1.00 should be capped at 1.00, and values of N greater than 4 should be capped at 4, for use in Equation 34. Also note that Equation 34 does not explicitly account for differences in significant weather events between facilities and regions.
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H. Freeway Analyses 59 Speed Harmonization Variable speed limit and speed harmonization installations are intended to give drivers advance notice of downstream slowing and to provide recommended speeds for upstream drivers to reduce the shockwaves on freeways.
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60 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual 11. References Cambridge Systematics, Inc.
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61 I Multilane Highways 1.
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62 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual 4. Scoping and Screening Method Generalized Service Volume Table Whether or not a more detailed multilane highway analysis is needed can be determined by comparing the counted or forecasted peak hour or daily traffic volumes for the sections of the highway between each major intersection to the values given in Exhibit 30.
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I. Multilane Highways 63 casted volumes for a section fall below the agency's target LOS standard, then the section can be excluded from a more detailed analysis.
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64 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual where fHV = heavy vehicle adjustment factor (decimal) , PHV = percentage heavy vehicles (decimal)
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I. Multilane Highways 65 The most-accurate method for estimating free-flow speed is to measure it in the field under low-flow (less than 1,000 vehicles per hour per lane)
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66 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual resources and the accuracy is likely to be sufficient for most planning and preliminary engineering applications. Level of Service The HCM does not define LOS at a facility level for multilane highways.
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I. Multilane Highways 67 ( )
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68 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual = × 3,600 Equation 43target,section section target,section TT L S ( ) = + − × ≥ 3,600 0 Equation 44section section target,section section,thru VHD TT d TT Vthru ∑= Equation 45facilityVHD VHDii where TTtarget, section = target travel time for a section (s)
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I. Multilane Highways 69 8.
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70 J Two-Lane Highways 1.
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J. Two-Lane Highways 71 way facilities, combining the operations of sections with signalized intersections, stop-controlled intersections, or roundabouts.
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72 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual is required to ascertain the performance of the highway. At present, the HCM does not provide such an analysis procedure, so the analyst would have to resort to microsimulation or some other system analysis approach.
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J. Two-Lane Highways 73 fHV, fHV,0 = desired and initial adjustment factors, respectively, for presence of heavy vehicles in the traffic stream, PHF, PHF0 = desired and initial peak hour factors, respectively, K, K0 = desired and initial proportions, respectively, of daily traffic occurring during the peak hour, and D, D0 = desired and initial proportions, respectively, of traffic in the peak direction during the peak hour.
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74 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual recreational areas. On such sections, local traffic often mixes with through traffic, and the density of unsignalized roadside access points is noticeably higher than in a purely rural area.
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J. Two-Lane Highways 75 6.
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76 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual All of these approaches for estimating free-flow speed assume all vehicles have the same posted speed limit. Should the posted speed limit for trucks or other vehicle classes be lower than that for other vehicle types, the analyst will have to apply some judgment based on local experience when employing the above methods to estimate free-flow speed.
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J. Two-Lane Highways 77 Equation 50 is used to estimate average speed without the effects of passing lanes.
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78 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Lnpl = total length of the section not influenced by passing lanes (mi) , and Lsection = total section length (mi)
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J. Two-Lane Highways 79 VHDsection = vehicle-hours of delay to through vehicles in a section (veh-h)
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80 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual 8. Multimodal LOS Bicycle LOS The HCM provides a bicycle LOS measure for two-lane highways.
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81 K Urban Streets 1.
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82 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual 3. Analysis Methods Overview Urban street performance can be directly measured in the field or it can be estimated in great detail using microsimulation.
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K. Urban Streets 83 Because all of these methods still require a fair amount of data and computations, this chapter also provides a high-level service volume and volume-to-capacity ratio screening method for quickly identifying which portions of the street will require more detailed analysis (to properly account for the spillover effects of congestion)
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84 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual scoping purposes to identify those intersections requiring more detailed analysis. They may also be used to quickly screen capacity-related improvement alternatives.
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Exhibit 46. Daily and peak hour service volume and capacity table for four-lane urban streets.
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86 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Sensitivity of Predicted Urban Street Speeds Analysts should be aware of the following sensitivities of the HCM urban street estimation method: • The HCM-predicted average speeds under low-flow conditions may be higher or lower than the posted speed limit, depending on the posted speed limit and the signal spacing. • For through movement v/c ratios below 1.00, average speeds are much more sensitive to changes in v/c ratios than are freeways and highways.
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K. Urban Streets 87 Exhibit 48.
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88 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Input Requirements The method requires data for four input parameters: 1. The through movement volume along the segment vm (veh/h)
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K. Urban Streets 89 NTH = number of through lanes, and s = saturation flow rate for the through movement (veh/h/ln)
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90 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Step 5: Calculate the Average Travel Speed and Determine Level of Service The average travel time on the segment TT is calculated using Equation 64. Equation 64T t dT R= + where TT = average though movement travel time (s)
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K. Urban Streets 91 Exhibit 51.
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92 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual line during the green interval is equal to the saturation flow rate. The slope of the capacity line is the product of the saturation flow rate and the green ratio.
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K. Urban Streets 93 through traffic on the segment.
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94 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual conditions described in HCM Chapter 30. The method includes nine steps, shown in Exhibit 56 and described below.
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K. Urban Streets 95 The available queue storage Qa is compared to the estimated maximum queue (computed later)
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96 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Step 7: Calculate Queue Clearance Rate The rate of queue clearance rqc during analysis period 2 is calculated as follows: Equation 722r c vqc TH= − where rqc = rate of queue clearance (veh/h) during analysis period 2, cTH = through movement capacity at the downstream signal (veh/h)
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K. Urban Streets 97 Computational Tools A spreadsheet has been developed for use in calculating each of the data elements.
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98 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual 10. References Elefteriadou, L., Z
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99 L Signalized Intersections 1.
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100 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Employing the HCM method with defaults identified in HCM Chapter 19 reduces the data requirements, but still requires specialized software to implement the complex computations. As indicated by the unshaded boxes in Exhibit 59, this section presents a medium-level method for evaluating signalized intersections, portions of which can be used to perform a high-level screening and scoping analysis to focus the planning and preliminary engineering analysis on only those intersections and time periods requiring investigation.
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L. Signalized Intersections 101 Parking activity at the intersection is characterized as either allowed or prohibited (default)
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102 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual • Split phasing means that all movements on an approach, including the left turns, proceed at the same time with no opposing movements. The analyst can select one of these four phasing types if the phasing is known.
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L. Signalized Intersections 103 Step 3a: Heavy Vehicle Adjustment The adjustment for heavy vehicles EHVadj is calculated using Equation 75.
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104 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual E E g E g g g LT LT prot LT prot LT perm LT perm LT prot LT perm ( )
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L. Signalized Intersections 105 guidance on the magnitude of these other effects on saturation flow rates.
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106 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual assessed independently. The combination of movements that make up the critical movements are different for protected and permitted left-turn phasing, and for split phasing.
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L. Signalized Intersections 107 of all lane groups for that approach.
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108 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual where Xc = critical volume-to-capacity ratio (unitless) , Vc = critical intersection volume (tpc/h/ln)
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L. Signalized Intersections 109 Step 6b: Calculate the Total Effective Green Time The total effective green time gTOT available during the cycle is calculated using Equation 90.
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110 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual requirements and other considerations such as the minimum green time and the time required for pedestrians to cross the approach. All green time and cycle length calculations should be adjusted to meet minimum requirements for all users.
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L. Signalized Intersections 111 The unsignalized movement delay dunsig is the average delay (if any)
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112 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Q d c = × 3,600 Equation 99 1 where Q = deterministic average queue for the lane group (tpc/ln) , d1 = uniform delay for the lane group (s)
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L. Signalized Intersections 113 Signalized Intersection Planning Method (Part 1)
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114 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Signalized Intersection Planning Method, Protected-Permitted Left-Turn Worksheet NB SB EB WB gLTPT gLTPM ELTPT ELTPM ELTC VLTTOT VLTPT Notes: NB = northbound, SB = southbound, EB = eastbound, WB = westbound. Exhibit 73.
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115 M Stop-controlled Intersections 1.
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116 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual 4. Simplified HCM Method for All-Way Stop-controlled Intersections An AWSC intersection is an intersection in which all movements are Stop-controlled.
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M. Stop-controlled Intersections 117 Delay Estimation The delay on each approach of an AWSC intersection is estimated by entering the Street 1 (subject approach)
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118 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual 5. Simplified HCM Method for Two-Way Stop-controlled Intersections A TWSC intersection is an intersection where the movements on one street (the minor street)
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M. Stop-controlled Intersections 119 • Intersection peak hour factor PHF for the intersection, either supplied by the analyst or assuming a default value of 0.92.
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120 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Step 3: Determine Conflicting Flows Each non–rank 1 movement faces a unique set of conflicting flows through which the movement must maneuver. For example, a minor street through movement conflicts with one higher ranked movement (its opposing major street left-turn movement)
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M. Stop-controlled Intersections 121 where vc,9, vc,12 = conflicting flow rates for movements 9 and 12, respectively (veh/h)
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122 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual The follow-up headway tf,x for each movement x is calculated using Equation 117. Equation 117, ,base ,t t t Pf x f f HV HV= + where tf,x = follow-up headway for movement x (s)
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M. Stop-controlled Intersections 123 where cm,j = movement capacity for Rank 2 movements j ( j = 1, 4, 9, or 12)
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124 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual where cSH = shared lane capacity of a minor street approach (veh/h) , vy = demand flow rate of movement y in the subject shared lane (veh/h)
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M. Stop-controlled Intersections 125 7.
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126 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual All-Way STOP Control (AWSC) Intersec on Planning Method Worksheet Approach NB SB EB WB Turning movement LT TH RT LT TH RT LT TH RT LT TH RT Volume Lanes Delay Delay Notes: NB = northbound, SB = southbound, EB = eastbound, WB = westbound, LT = le turn, TH = through, RT = right turn.
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M. Stop-controlled Intersections 127 9.
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128 N Roundabouts 1.
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N. Roundabouts 129 Data Needs, Assumptions, and Limitations The following assumptions and limitations apply to the simplified HCM planning method for roundabouts: • No pedestrians, • No bypass lanes, and • No more than two lanes within the roundabout and on any entry.
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130 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Step 2: Heavy Vehicle Adjustment Demand flow rates in vehicles per hour are adjusted for the presence of heavy vehicles using Equation 134 and Equation 135, producing adjusted flow rates in passenger cars per hour (pc/h)
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N. Roundabouts 131 where vc,xx,pce = circulating flow rate opposing approach direction xx (pc/h)
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132 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual c c fj j pce HV= Equation 141, where vj = demand flow rate for lane j (veh/h) , vj,pce = adjusted flow rate for lane j (pc/h)
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N. Roundabouts 133 Step 8a: Calculate Average Control Delay per Entry Lane.
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134 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual = 3,600 Equation 146Q d c A where QA = deterministic average queue on approach (veh) , d = average control delay on approach (s/veh)
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N. Roundabouts 135 Percentile Demand (veh/h)
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136 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual 7. Multimodal LOS The HCM does not provide bicycle, pedestrian, transit, or truck LOS measures for roundabouts.
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137 O Pedestrians, Bicyclists, and Public Transit 1.
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138 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Transit Buses operating on freeways in level terrain will generally operate at the same speed as other vehicular traffic, although buses designed to primarily operate on urban streets may not have the power to travel at higher freeway speeds (e.g., over 55 mph)
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O. Pedestrians, Bicyclists, and Public Transit 139 4.
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140 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual As noted above, the pedestrian LOS methodology requires a number of input values, but most of these can be defaulted, particularly when local default values have been established for different combinations of roadway functional class and area type. The calculations can be performed by hand or (preferably when large numbers of segments will be evaluated)
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O. Pedestrians, Bicyclists, and Public Transit 141 along a street segment, including intersection and street crossing effects.
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142 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual %OSP = percent of segment with occupied on-street parking (percent) , fB = buffer area coefficient (unitless)
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O. Pedestrians, Bicyclists, and Public Transit 143 should use caution if applying the pedestrian LOS methodology to facilities that are not ADA compliant.
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144 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Bicycles The HCM provides two bicycle performance measures for urban street segments and facilities: average travel speed (reflecting intersection delays) and a bicycle LOS score (reflecting bicyclist comfort with the bicycling environment)
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O. Pedestrians, Bicyclists, and Public Transit 145 As noted, the bicycle LOS methodology requires a number of input values, but most of these can be defaulted, particularly when local default values have been established for different combinations of roadway functional class and area type.
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146 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual WT = width of the outside through lane, bicycle lane if present, and paved shoulder if present (ft) ; a parking lane can only be counted as shoulder if 0% occupied (see Exhibit 102)
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O. Pedestrians, Bicyclists, and Public Transit 147 • Bicycle link LOS is used to characterize the segment (intersection plus link)
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148 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual but a lower-passenger-volume stop with short green times for buses or that experiences high right-turning traffic volumes can also be the critical stop. Bus capacity is calculated using Equation 150 and Equation 151, adapted from the TCQSM: 3,600 Equation 150B N f g C t t g C Zc t el tb c d v d ( )
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O. Pedestrians, Bicyclists, and Public Transit 149 g/C = ratio of effective green time to total traffic signal cycle length (decimal)
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150 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual bus speed is calibrated to maximum capacity and therefore uses a 25% (maximum practical) failure rate in its calculation.
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O. Pedestrians, Bicyclists, and Public Transit 151 bus travel time rate, in minutes per mile, is calculated for the condition in which a bus moves along a street without traffic or traffic signal delays, with the only source of delay being stops to serve passengers.
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152 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual t N a a d acc dc s = + 5,280 0.5 Equation 158, 2 v a t max acc dc = × 1.47 Equation 159 , where tacc,dc = distance-constrained acceleration time (s) , Ns = average stop spacing (stops/mi)
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O. Pedestrians, Bicyclists, and Public Transit 153 estimated from Exhibit 110.
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154 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Total bus stop delay in the segment is calculated as follows: d N t t t tbs s dt acc dec re( ) = + + + Equation 164 where dbs = total bus stop delay in the segment (s)
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O. Pedestrians, Bicyclists, and Public Transit 155 can be performed by hand or (preferably when large numbers of segments will be evaluated)
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156 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual = × − Equation 168s f fw r h ptt where sw-r = transit wait–ride score (unitless) , fh = headway factor (unitless)
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O. Pedestrians, Bicyclists, and Public Transit 157 ATR = amenity time rate (min/mi)
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158 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Simplifications from the HCM The HCM method for estimating transit level of service for urban streets is documented in HCM Chapters 16 (Urban Street Facilities) , 18 (Urban Street Segments)
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O. Pedestrians, Bicyclists, and Public Transit 159 sures and provides suggested default values.
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160 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Bicycle Delay When bicyclists share the lane with automobile traffic, bicyclist delay is the same as automobile delay and can be calculated using Equation 97 (see Section L5)
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O. Pedestrians, Bicyclists, and Public Transit 161 When a pedestrian refuge area is available in the street median, pedestrians can cross the street in two stages.
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162 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual All-Way Stops The HCM 2016 provides a qualitative discussion of contributors to pedestrian delay at all-way stop-controlled intersections. However, the research base does not exist to provide a calculation method.
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O. Pedestrians, Bicyclists, and Public Transit 163 Pedestrians on an Exclusive Off-Street Facility Pedestrian LOS on an exclusive facility is based on the average space available to pedestrians.
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164 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Ap = average pedestrian space (ft 2/p) , and Sp = average pedestrian speed (ft/min)
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O. Pedestrians, Bicyclists, and Public Transit 165 The calculation process requires a large number of computations, and the use of a computational engine is recommended.
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166 P Truck Level of Service 1.
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P. Truck Level of Service 167 where U(x)
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168 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual time of writing, guidelines on establishing freight facility classes had not yet been developed. Until these guidelines are set, Exhibit 118 provides a tentative three-class system that employs some of the general criteria outlined in MAP-21 for classifying highway facilities by their relative importance to the regional and national economy.
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P. Truck Level of Service 169 The average peak hour truck TTI is estimated from the peak hour auto speed by applying a local adjustment factor fLA to reflect local driving characteristics.
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170 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual estimated probability of on-time arrival (POTA) , the estimated utility for trucks, and the %TLOS index.
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