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Pages 99-114

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From page 99...
... 99 This section presents the recommended methodology for estimating truck speeds on arterial segments in between signalized intersections. 9.1 Existing Truck Treatment on Arterials in the HCM Arterial analyses in the HCM (including signalized intersections, stop-controlled intersections, and roundabouts)
From page 100...
... 100 incorporating truck Analysis into the Highway capacity Manual For each segment, the base free-flow speed is computed using HCM Equation 17-2: Equation 480 0S S f ff CS A= + + where Sfo = the base free-flow speed, S0 = a constant, fCS = an adjustment for cross section, and fA = an adjustment for the access points. It would be possible to add an adjustment here for the truck mix, but this is not presently our first choice.
From page 101...
... Prediction of Arterial Truck Speeds 101 Nap = the number of influential access point approaches along the segment, and dother = delay due to other sources along the segment. For an overall arterial, the base free-flow speed is computed via Equation 52, 1 , 1 S L L S fo F ii m i fo i i m ∑ ∑ = = = where Sfo,F = the base free-flow speed for the facility, Li = the length of segment i, m = the number of segments on the facility, and Sfo,i = the base free-flow speed for segment i.
From page 102...
... 102 incorporating truck Analysis into the Highway capacity Manual 9.2 Approach The new methodology captures the effects of trucks on arterial speeds in two places. The first is at the intersection where the through-delay and through-stop rate are determined for point facilities like signalized intersections.
From page 103...
... Prediction of Arterial truck Speeds 103 9.4.1 Test Site Selection The investigation of the arterial segment midblock speed flow effects of trucks on extended grades was performed on a hypothetical arterial with no signals, consisting of 8 miles of level 6-lane street followed by 5 miles of 6-lane street with a grade. The grade on the 5-mile section varied from –6% to +6% in 1% increments (13 grades total)
From page 104...
... 104 incorporating truck Analysis into the Highway capacity Manual 0 500 1000 1500 2000 2500 3000 0 10 20 30 40 50 60 70 Fl ow R at e pe r L an e (v eh /h r) Density per Lane (veh/mi)
From page 105...
... Prediction of Arterial truck Speeds 105 The data points marked "Scenario" are the average mixed speeds for the 30% truck condition. At low flow, they are scattered between 40–50 mph, but they quickly drop to around 20 mph (the truck crawl speed)
From page 106...
... 106 incorporating truck Analysis into the Highway capacity Manual sto = the truck-only speed that would arise at flow rate v (again taking into account the PCE values for the mixed flow case and the all-truck case) , vm = the flow rate at which the automobile speed has accomplished half of its transition from sao to sto, DV = the range of flow rates over which the transition occurs, and b = a calibration coefficient that ensures the following holds true: 2 5 2 5 Equation 56 v V V and v V V m m −β − ∆ ∆ = − β + ∆ ∆ = − This ensures that the logit term within the large parentheses is approximately equal to 1 when v = vm – DV/2 and equal to 0 when v = vm + DV/2.
From page 107...
... Prediction of Arterial truck Speeds 107 If (%Grade>=1%) , then vm = 920 – 0.3475 *
From page 108...
... 108 Incorporating Truck Analysis into the Highway Capacity Manual Hoosick Street has two through-lanes in each direction plus left-turn bays. The side streets have one through-lane on each approach plus left-turn bays.
From page 109...
... Prediction of Arterial truck Speeds 109 p.m. peaks have been studied as well as hypothetical situations involving near-capacity flows in both directions and 15% and 30% trucks.
From page 110...
... 110 incorporating truck Analysis into the Highway capacity Manual 8th-10th 10th-TP TP-15th 15th-BD BD-25th 25th-Lake Number of Lanes 3 3 2 2 2 2 Length (ft) 531 797 521 1312 1430 1725 Grade (%)
From page 111...
... Prediction of Arterial truck Speeds 111 A set of monitoring points was superimposed on the omni-directional videotape images (Exhibit 73)
From page 112...
... 112 incorporating truck Analysis into the Highway capacity Manual In FHWA's roundabout design guide, Roundabouts: An Informational Guide, this relationship is employed to develop guidelines for roundabout diameters and vehicle speeds. Exhibit 74 shows the numerical guidance presented in Exhibit 6-14 of the guide (FHWA, 2000)
From page 113...
... Prediction of Arterial truck Speeds 113 The differences in speeds on the circulating roadway are not quite so dramatic. Here the 80th percentile for large trucks is 15 mph, while for automobiles it is 20 mph.
From page 114...
... 114 incorporating truck Analysis into the Highway capacity Manual Resources did not permit the development of a model for predicting truck travel time reliability. However, the SHRP2-L08 methodology (Kittelson and Vandehey, 2012)

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