TTE4004%20HW3%20Solution - Traffic composition - The effect...

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Traffic composition - The effect of large or heavy vehicles in the traffic stream reduces the maximum flow on the highway because of their operating characteristics; a heavy vehicle occupies more space in the traffic stream than does a passenger car. Grade - The effect of a grade depends on the length and slope of the grade. Traffic operations are significantly affected when grades of3% or greater are 0.25 mile or greater in length and when grades of 3% or less are greater than 0.5 mile in length. The effect of grades on heavy vehicles is much greater than on passenger cars. Driver population - A driver population consisting primarily of weekday commuters will have significantly different behavior than a driver population consisting of drivers unfamiliar with the roadway. For example, recreational traffic capacities can be as much as 20% lower than commuter traffic capacities. Interchange spacing - As interchanges are more closely spaced, the lengths of basic freeway segments unaffected by interchanges decreases as the weaving movements at interchanges have an increasing impact on traffic flow resulting in a reduction of speeds. 9-12 Given: Freeway; design volume of 5000 veh/h; PHF: 0.9; trucks: 10%; design LOS: C; free flow speed: 70 mi/h; no lateral obstructions; rolling terrain; interchange spacing: 3 mi. Determine: Number of 12 ft lanes required in each direction. Step 1: Compute passenger car equivalent flow rate for peak 15-minute period using Equation 9.21. Determine fp(driver population factor); assume mainly commuter traffic, fp= 1.0 Determine ET(PCE for trucks), using Table 9.25; ET= 2.5 Determine ER(PCE for RVs), using Table 9.25; ER = 2.0 Determine fHV(heavy vehicle adjustment factor), using Equation 9.4 1 1 J: v = = = 0.87 H I+Pr(Er -1)+PR(ER -1) 1+0.10(2.5-1)+0.00(2.0-1) Step 2: Assume six lanes (three in each direction) V vp = - (5000)/(0.90)(3)(0.87)(1.0) = 2128 pc/h/ln (PHF)(N)(IHV )(Ip) Step 3: Compute free flow speed using Equation 9.23 FFS = BFFS - fiw - fie -IN - lID Determine fLwusing Table 9.34, fLw= 0.0 Determine fLcusing Table 9.35, fLc= 0.0 Determine fNusing Table 9.36, fN = 3.0 Determine fIDusing Table 9.37, fID= 0.0 FFS = 70- 0.0- 0.0- 3.0- 0.0 = 67.0 mi/h 91 Traffic and Highway Engineering, Third Edition: Instructor's Manual Garber and Hoel
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p Step 4: Compute average passenger car speed and density to determine LOS. For FFS = 67 mi/h and vp= 2128 pc/h/1n,using Figure 9.9, the average passenger car speed, S = 60.0 mi/h Density = (2128 pc/h/ln) /60.0 mi/h = 35.4 pc/mi/ln Using Table 9.33, this density corresponds to LOS E, therefore, a three lane section is inadequate. Repeat steps 2 and 3. Step 2: Assume eight lanes (four in each direction) vp = V - (5000)/(0.90)(4)(0.87)(1.0) = 1597 pc/h/ln (PHF)(N)(IHV )(Ip) .1i1 Step 3: Compute free flow speed using Equation 9.23 FFS = BFFS - fLw - fLc -IN - lID Determine fLwusing Table 9.34, fLw = 0.0 Determine fLcusing Table 9.35, fLc= 0.0 Determine fNusing Table 9.36, fN = 1.5 Determine fIDusing Table 9.37, fID
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TTE4004%20HW3%20Solution - Traffic composition - The effect...

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