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Pages 115-133

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From page 115...
... 115 S e c t i o n 1 0 This section describes the research relating to the effects of trucks on the capacity of freeways, arterial street segments, roundabouts, and signalized intersections. Recommended updates to the current HCM passenger car equivalents (PCEs)
From page 116...
... 116 incorporating truck Analysis into the Highway capacity Manual that flow rate, an all-automobile density of 21 veh/mile/lane is identified and based on that, assign a density-based LOS. The densities observed in the field are likely to always be higher than those anticipated by the all-automobile model.
From page 117...
... Predicting the effect of trucks on capacity 117 pa = proportion of automobiles in traffic stream (decimal) ; pt = proportion of trucks in traffic stream (decimal)
From page 118...
... 118 incorporating truck Analysis into the Highway capacity Manual The t-critical value is 1.97. The t-statistic values for the coefficients are all greater than this value; therefore all of the independent variables are relevant in predicting the PCE value.
From page 119...
... Predicting the Effect of Trucks on Capacity 119 However, since 1∑ ∗ =P PT T T i i , then Equation 72 can be simplified to: 1 1 1 Equation 73 ∑ ∑ ∑ ∑ ∑ = = − +       = − +      E P E P P E P P P P E P T T T T T T T T T T T T T T T T T i i i i i i i i i i i i i Hence, E˜T is given by the percentage weighted average of the ETi values. Application of this technique is illustrated in Exhibit 78 for a freeway.
From page 120...
... 120 incorporating truck Analysis into the Highway capacity Manual for the WIM station located on U.S. 421 just south of the interchange with U.S.
From page 121...
... Predicting the effect of trucks on capacity 121 Oakland, California, and Miami, Florida, were used to develop and calibrate the VISSIM microsimulation program. The calibrated simulation was then applied in several scenarios to develop the truck PCE sensitive to the truck proportion and the grade at signalized intersections.
From page 122...
... 122 incorporating truck Analysis into the Highway capacity Manual Selection of Test Sites Two test sites were selected, both at major maritime ports, so as to obtain high semitrailer truck volumes. The Maritime Street site is located on a major access road to the Port of Oakland, California.
From page 123...
... Predicting the effect of trucks on capacity 123 Sample Test 1 -- Variation of Truck Proportion under a Fixed Truck Mix. In this test the impact of the truck proportion was investigated for 0 grade.
From page 124...
... 124 incorporating truck Analysis into the Highway capacity Manual simulation run was replicated 10 times to account for the stochastic variability of the microsimulation program. The following scenarios were tested: • Weight-to-horsepower ratio: 150 lbs/hp; • Truck mix: 50% single-unit trucks, 50% semitrailer trucks; • Truck proportion: 10%, 20%, 30%, 40%, 50%; and • Grade: –4%, –2%, 0, 2%, 4%, 6%, 8%, 10%.
From page 125...
... Predicting the effect of trucks on capacity 125 Exhibit 82. Saturation flow rate by grade and truck% for 50:50 mix Class 5 and Class 9 trucks.
From page 126...
... 126 incorporating truck Analysis into the Highway capacity Manual This model is valid for the range of trucks between 0% and 50% of the traffic stream, for grades between and including –4% and +10%. Exhibit 84 shows the predicted PCE values for the same mixture of grades and truck proportions.
From page 127...
... Predicting the effect of trucks on capacity 127 Exhibit 85. Signalized approach PCE values -- 75% Class 5 and 25% Class 9 trucks.
From page 128...
... 128 incorporating truck Analysis into the Highway capacity Manual 10.4.5 Comparison with HCM Signalized Intersection Truck PCEs The findings from the analysis of the simulation results indicate that the PCE values at signalized intersections depend on the truck characteristics, proportions, and approach grade. The impacts of trucks on saturation flows (and capacities)
From page 129...
... Predicting the effect of trucks on capacity 129 HV% = the percentage of heavy vehicles in traffic stream (%) ; and G% = the percent grade (%)
From page 130...
... 130 incorporating truck Analysis into the Highway capacity Manual (shown in HCM Exhibit 21-10, which is not repeated here) makes PCE-based adjustments for heavy vehicles.
From page 131...
... Predicting the effect of trucks on capacity 131 For the move-up time analysis, the events representing arrival into first position in the righthand lane were studied. Headways were computed between successive vehicles.
From page 132...
... 132 incorporating truck Analysis into the Highway capacity Manual these headways are not sustainable, as the diagram suggests. If they were, the CDFs would be vertical at those values.
From page 133...
... Predicting the effect of trucks on capacity 133 and the values for ln(c0) and b can be found via log-linear regression based on the following equation: ln ln Equation 810c c ventry conflicting( )

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