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Class_35_Two-Lane_LOS_and_Capacity

# Class_35_Two-Lane_LOS_and_Capacity - The Pennsylvania State...

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The Pennsylvania State University Department of Civil and Environmental Engineering CE 321: Highway Engineering Class 35 -- Two Lane Highway Capacity Analysis Spring 2008

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Introduction Two-lane highways are roads with one available lane in each direction. Consider traffic in both directions. Geometric features may restrict passing sight distance. Terrain is a critical factor in analysis. Two analysis types: Directional Two-way (focus of CE 321)
Scope of HCM Methodology Two-way segments Homogeneous cross-section Relatively constant demand volumes Level or rolling terrain Directional segments Specific upgrades or downgrades Consider vertical curves in analysis Consideration of passing lanes

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Base Conditions 12-ft lane widths 6-ft shoulder widths 0% no passing zones Passenger cars only No direct access points No traffic control or turning vehicle impediments Level terrain (grades < 2%) Directional split = 50/50
Capacity and LOS of Two-lane Highways Capacity is 1,700 pc/hr for each direction Capacity is 3,200 pc/hr for both directions LOS Class I (mobility) » Percent-time-spent-following » Average travel speed Class II (serve shorter trips) » Percent-time-spent-following

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LOS for Class I Highways LOS Percent-time- Spent-following Avg. Travel Speed (mph) A < 35 > 55 B > 35 to 50 > 50 to 55 C > 50 to 65 > 45 to 50 D > 65 to 80 > 40 to 45 E > 80 < 40 Table 6.21 in Principles of Highway Engineering and Traffic Analysis, 3 rd Edition
LOS for Class II Highways LOS Percent-time- Spent-following A < 40 B > 40 to 55 C > 55 to 70 D > 70 to 85 E > 85 Table 6.22 in Principles of Highway Engineering and Traffic Analysis, 3 rd Edition

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HCM Methodology for Two-lane Segments
Determination of Free-flow Speed Measure of traffic under low-flow conditions Less than 200 pc/h total for both directions Free-flow speeds of 45 to 65 mph Can be measured or estimated Field measurement: Sample all or systematic sample Less than 200 vph » Adjust if at site with > 200 vph

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Class_35_Two-Lane_LOS_and_Capacity - The Pennsylvania State...

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