Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual (2016) / Chapter Skim
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From page 188... ...
P A R T 4 Case Studies This part presents three case studies illustrating the application of the HCM to typical planning and preliminary engineering studies. Case Study 1: Freeway Master Plan • Overview • Example 1: focusing the study -- screening for service volume problems • Example 2: forecasting v/c hot spots • Example 3: estimating speed and travel time • Example 4: predicting unacceptable motorized vehicle LOS hot spots • Example 5: estimating queues • Example 6: predicting reliability problems • Example 7: comparison of overcongested alternatives Case Study 2: Arterial BRT Analysis • Overview • Example 1: preliminary screening with service volume tables • Example 2: computing critical intersection v/c ratios • Example 3: calculation of intersection v/c ratio for permitted left turns • Example 4: estimating auto and BRT speeds • Example 5: predicting queue hot spots • Example 6: pedestrian, bicycle, and transit LOS Case Study 3: Long-Range Transportation Plan Analysis • Overview • Example 1: estimating free-flow speeds and capacities for model input • Example 2: HCM-based volume–delay functions for model input • Example 3: Predicting density, queues, and delay • Example 4: Predicting reliability
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195 T Case Study 1: Freeway Master Plan 1.
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196 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual U.S. 101 carries between 20,000 and 74,000 AADT, depending on location.
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T. Case Study 1: Freeway Master Plan 197 In this case, it will turn out that the traffic flow and geometric characteristics of the supersections generally correspond well with the defaults assumed in the construction of the HCM's generalized daily service volume tables in HCM Chapter 12, Basic Freeway and Multilane Highway Segments (HCM Exhibits 12-39 through 12-42)
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198 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual This process results in the 70-mile facility being split into nine supersections (A–I) , as illustrated in Exhibit 135.
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T. Case Study 1: Freeway Master Plan 199 Exhibit 32 (multilane highway required data)
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200 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Step 3: Compute Peak Hour, Peak Direction Demands Each supersection's bi-directional AADT is multiplied by the supersection's K- and D-factors. The result is the supersection's peak hour demand in the peak direction, shown in row 14 of Exhibit 136.
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T. Case Study 1: Freeway Master Plan 201 service volume for each supersection (Rows 29–32)
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Exhibit 137. Case study 1: map of supersection C
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T. Case Study 1: Freeway Master Plan 203 Section-specific inputs consist of segment type, segment length, number of directional lanes, and directional demand AADT.
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204 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Equation 17 also assumes that the first and third 15-minute intervals within the peak hour will have average flow rates for the peak hour, while the last 15-minute interval will have a lowerthan-average flow rate such that the sum of the demands of the four intervals will equal the total hourly demand. The demands for other intervals within the peak hour need to be calculated when performance measures such as duration of congestion or queue length are to be computed, as demand that cannot be served in one 15-minute interval must be carried over to the next interval.
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T. Case Study 1: Freeway Master Plan 205 Exhibit 141 presents the calculations for all sections.
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206 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual in subsequent examples. Steps 4–6 are repeated for each 15-minute interval within the peak hour, with any unserved demand in a section carried over into the next interval.
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T. Case Study 1: Freeway Master Plan 207 4.
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208 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual section will be added to the section's travel time at free-flow speed to reflect congestion effects. Delay rates are computed separately for undersaturated (d/c ≤ 1.00)
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T. Case Study 1: Freeway Master Plan 209 3,600 3,600 0.24 65 0.24 6.9 0 14.9 s-3,1 -3 -3 3 -3,1 -3,1T L FFS LC C C C RU ROC C( )
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210 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Step 2: Interpreting Speed Results The computed average speeds can be used to generate a contour diagram similar to the one shown in Exhibit 149 for spotting a speed range that indicates section congestion. By the visual method, the analyst will be able to determine which sections experience low speeds, and for how long.
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T. Case Study 1: Freeway Master Plan 211 section C-4 in time period 1, the demand served is 4,212 veh/h (Exhibit 143)
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212 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Section C-1 C-2 C-3 C-4 C-5 C-6 C-7 Section type Basic Ramps Basic Ramps Basic Ramps Basic Number of lanes 2 2 2 2 2 2 2 Time Period 1 Served demand (veh/h) 3,336 4,024 3,984 4,212 3,865 3,977 3,865 Speed (mph)
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T. Case Study 1: Freeway Master Plan 213 spots during the weekday p.m.
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214 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Step 2: Interpreting the Results The planning-level freeway facility method does not contain a queue propagation algorithm, which explains why freeway sections C-2 and C-4 have queue lengths exceeding the section length. As such, the measure of "percent segment queued" is only meaningful up to 100%.
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T. Case Study 1: Freeway Master Plan 215 Step 5: Compute the Recurring Delay Rate The recurring delay rate for the facility is computed using Equation 33, found in Section H7 of the Guide.
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216 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual section within the facility exceeds capacity. The number of lanes is limited to 2, 3, or 4.
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T. Case Study 1: Freeway Master Plan 217 Step 9: Compute Percent Trips Under 45 mph The percent of peak hour trips over the year that travel at average speeds below 45 mph for the facility is computed using Equation 36.
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218 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Section C-1 C-2 C-3 C-4 C-5 C-6 C-7 Section type Basic Ramps Basic Ramps Basic Ramps Basic Section capacity (veh/h) 4,434 4,212 4,434 4,212 4,434 4,212 4,434 Time Period 1 Mainline demand (veh/h)
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T. Case Study 1: Freeway Master Plan 219 Section C-1 C-2 C-3 C-4 C-5 C-6 C-7 Section type Basic Ramps Basic Weave Basic Ramps Basic Section capacity (veh/h)
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220 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual CAF V Lr s= − + ≤0.884 0.0752 0.0000243 1.00weave CAF ( )
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T. Case Study 1: Freeway Master Plan 221 Again, the results are ambivalent until one compares the worst case d/c ratio under each alternative.
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222 U Case Study 2: Arterial BRT Analysis 1.
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U. Case Study 2: Arterial BRT Analysis 223 • Example 4: Estimating Auto and BRT Speeds • Example 5: Predicting Queue Hot Spots • Example 6: Pedestrian, Bicycle, and Transit LOS The HCM does not currently address the analysis of truck LOS for urban streets, so truck LOS analysis is excluded from this case study.
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224 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Step 2: Obtain AADT Estimates for Supersections In this example, AADT volumes are not available for each supersection, but peak hour counts are available, as are data from a few permanent traffic recorders located on other arterial streets. These traffic recorders indicate that typical peak hour traffic in the area is approximately 10% of the daily traffic and that 55% of peak hour traffic travels in the peak direction.
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U. Case Study 2: Arterial BRT Analysis 225 LOS for the screening.
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226 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Step 0: Assemble Data The turning-movement volumes and lane configurations for the six major intersections in supersection C were shown in Exhibit 165. According to Exhibit 60 in Section L3 of the Guide, the following additional data are required to evaluate capacity: • Peak hour factor, • Percent heavy vehicles, • Parking activity, and • Pedestrian activity.
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U. Case Study 2: Arterial BRT Analysis 227 • Left-turn volume exceeds 240 veh/h; • The product of the left-turn volume and the opposing through volume exceeds a given threshold (50,000 if there is one opposing through lane, 90,000 if there are two opposing through lanes, and 110,000 if there are three or more opposing through lanes)
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228 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Step 3: Convert Turning Movements to Through Passenger Car Equivalents This step converts turning movements to through passenger car equivalents, considering the effect of heavy vehicles, variations in traffic flow during the hour, the impact of opposing through vehicles on permitted left-turning vehicles, the impact of pedestrians on right-turning vehicles, lane utilization, and the impact of parking maneuvers on through and right-turning vehicles. Step 3a: Heavy Vehicle Adjustment The adjustment for heavy vehicles EHVadj is calculated using Equation 75.
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U. Case Study 2: Arterial BRT Analysis 229 ELU = 1.00.
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230 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Similarly for the north–south approaches, the critical volume Vc,NS is calculated using Equation 81.
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U. Case Study 2: Arterial BRT Analysis 231 Step 0: Assemble Data The turning-movement volumes and lane configurations for this intersection were shown in Exhibit 165 in Example 2.
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232 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual right-turn and left-turn volumes on the approach are small relative to the through volume, so no de facto turn lanes exist and the original assignment of a mixed lane group is retained. Step 3: Convert Turning Movements to Passenger Car Equivalents This step converts turning movements to through passenger car equivalents, considering the effect of heavy vehicles, variations in traffic flow during the hour, the impact of opposing through vehicles on permitted left-turning vehicles, the impact of pedestrians on right-turning vehicles, lane utilization, and the impact of parking maneuvers on through and right-turning vehicles.
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U. Case Study 2: Arterial BRT Analysis 233 Step 3c: Turn Impedance Adjustment The turn impedance adjustment factors ELT and ERT adjust for impedances experienced by left- and right-turning vehicles, respectively.
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234 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual east–west approaches, the critical volume Vc,EW is calculated using Equation 82, while the critical volume for the north–south approaches Vc,NS is calculated using Equation 83.
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U. Case Study 2: Arterial BRT Analysis 235 times within each section and for supersection C as a whole.
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236 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual of 23.0 seconds for the parallel through movements. Therefore, the effective green time assigned to the westbound and eastbound movements is increased to 23.0 seconds and the effective green time assigned to the northbound and southbound movements is decreased to 89.0 seconds.
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U. Case Study 2: Arterial BRT Analysis 237 from Step 6b (Exhibit 172)
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238 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual there is no northbound left turn at these intersections, the southbound through movement can also move while the southbound left turn is being served; therefore, the effective green time used for the southbound through is the sum of the southbound left turn and northbound through effective green. Exhibit 173 provides the northbound and southbound delay calculation results for all signalized intersections in supersection C
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U. Case Study 2: Arterial BRT Analysis 239 Step 5: Compute the Average Travel Speed and Determine Level of Service The average travel time on the segment TT is calculated using Equation 64: 12.8 18.6 31.4 sT t dT R= + = + = The average travel speed on the segment ST,seg is calculated using Equation 65: 3,600 5,280 3,600 655 5,280 31.4 14.2 mph,S L T T seg T = × × = × × = From Exhibit 52, this speed corresponds to LOS D
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240 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual supersection C, at 49th Street. Section O4 of the Guide provides two options for estimating bus speeds: (1)
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U. Case Study 2: Arterial BRT Analysis 241 Step 3: Base Bus Speed The two running time rates calculated in Steps 1 and 2 are combined into a base bus running time rate tr using Equation 160 and a base bus speed Sb using Equation 161.
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242 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual For northbound Telegraph Avenue at 55th Street, the average queue computation is as follows: 3,600 27.0 1,034 3,600 7.8 8 tpc ln 1 Q d c = × = × = → The estimated 95th percentile queue would be 2 × 7.8 = 15.6 tpc/ln, which rounds to 16 tpc/ln. Exhibit 176 summarizes the results for both directions of Telegraph Avenue in supersection C
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U. Case Study 2: Arterial BRT Analysis 243 study.
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244 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Summary Pedestrian LOS Results for Supersection C (Northbound) Exhibit 177 presents the summary results for each northbound section in supersection C, following implementation of the BRT project.
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U. Case Study 2: Arterial BRT Analysis 245 section related inputs shown in Exhibit 101 are only required for a section-level analysis, and the segment length is only required for a facility-level analysis.)
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246 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual • The percentage of heavy vehicles HV in the direction of travel is 5%. Because the bicycle LOS score is highly sensitive to HV, the percentage of heavy vehicles in the exclusive bus lane (100%, capped at 50% by the methodology)
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U. Case Study 2: Arterial BRT Analysis 247 to parked cars.
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248 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual 4 local buses per hour)
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U. Case Study 2: Arterial BRT Analysis 249 Headway Factor.
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250 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual In the other sections, served only by local buses at stops without shelters or benches, the fPTT is 0.72. Transit Wait-Ride Score.
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U. Case Study 2: Arterial BRT Analysis 251 • The existing local bus service operates every 10 minutes, has an average peak hour load factor of 125%, and has a scheduled travel speed through supersection C of 6 mph.
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252 V Case Study 3: Long-Range Transportation Plan Analysis 1.
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V. Case Study 3: Long-Range Transportation Plan Analysis 253 2.
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254 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual Step 2: Identify Free-Flow Speeds The analyst then identifies the appropriate default free-flow speed to be assumed for each facility and area type. These speeds are generally rounded to the nearest 5 miles per hour for the purposes of the look-up table and the initial coding of the highway network.
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V. Case Study 3: Long-Range Transportation Plan Analysis 255 3.
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256 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual facility types and subtypes listed in Exhibit 185. In this case, the calibration parameters for the freeway basic sections in Exhibit 185 are selected to represent all freeway links in Exhibit 184.
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V. Case Study 3: Long-Range Transportation Plan Analysis 257 4.
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258 Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual compared to an agency specified minimum speed goal for each link. The speed goal may be the link free-flow speed, or some other value reflecting agency policy.
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V. Case Study 3: Long-Range Transportation Plan Analysis 259 Similarly, applying the data for Link A004 from Example 2, RDR is 0.0005, IDR is 0.0005, and TTIm is 1.07.
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Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing America's Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012)
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TRA N SPO RTATIO N RESEA RCH BO A RD 500 Fifth Street, N W W ashington, D C 20001 A D D RESS SERV ICE REQ U ESTED ISBN 978-0-309-37565-8 9 780309 375658 9 0 0 0 0 N O N -PR O FIT O R G .
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