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Multilane Highway Capacity Analysis

Multilane Highway Capacity Analysis. CE331 Transportation Engineering. Objectives. Determine LOS for multilane highways Determine number of lanes to ensure given LOS. Multilane Highways.

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Multilane Highway Capacity Analysis

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  1. Multilane Highway Capacity Analysis CE331 Transportation Engineering

  2. Objectives • Determine LOS for multilane highways • Determine number of lanes to ensure given LOS

  3. Multilane Highways Roadway facilities with some access control, usually in urban or suburban settings, with some flow interruptions, traffic signals at least 2.0 miles apart, with or without median, and lower design aspects than freeways

  4. Multilane Highways (cont’d) • Factors affecting the flow on multilane highways • Uncontrolled access from roadside • Left turns (not explicitly considered in analysis) • Types of multilane highways • Rural or suburban • Divided or undivided

  5. Multilane Highways

  6. “Ideal” Conditions • 12-foot lanes • 12-foot total right and left shoulders • Divided highway • Only passenger cars • Level terrain • No intersections • Everyday commuters • FFS >= 60mph

  7. Procedure for Determining LOS • Estimate free flow speed (FFS) • Calculate equivalent flow rate (vp) • Compute density (D=vp/S) and compare D to values in Exhibit 21-3 to determine LOS

  8. Free Flow Speed FFS = BFFS - fLW - fLC - fM - fA • Adjustment factors fLW – lane width adj. factor, Exhibit 21-4 fLC – lateral clearance adj. factor, Exhibit 21-5 fM – median type adj. factor, Exhibit 21-6 fA – access point adj. factor, Exhibit 21-7 • Base Free Flow Speed (BFFS) • No speed limit: 60 mph • Speed limit: +7 mph for SL 40 & 45 mph or +5 mph for SL>=50 mph • 85th Percentile speed: -1 for 40 mph to -3 for 60 mph

  9. L R C L R Lateral Clearance Adjustment Divided LC=Left+Right Shoulder fM =0; fLC Exhibit 21-5 Undivided LC=6+Right Shoulder fM = 1.6; fLC Exhibit 21-5

  10. Adjust for vehicle mix and users Equivalent Flow Rate (vp) V: directional hourly volume (vph) PHF: peak hour factor N: number of lanes in one direction fHV: heavy vehicle adj. factor fp: driver population adj. factor, mostly =1

  11. Heavy Vehicle Adj. Factor (fHV) PT – truck and bus percentage PR – recreational vehicle percentage ET – passenger car equivalent for trucks and buses, Exhibits 23-8, 23-9, 23-11 ER – passenger car equivalent for recreational vehicles, Exhibit 23-8, 23-10

  12. 1.9 0.0 0.0 2.0 50+5=55 Example 1 4-Lane suburban divided highway; V=1,750 vph; 5% trucks; 11-foot lanes; adequate clearance both sides; 2% grade; 1.5 miles; 12 intersections; PHF 0.9; speed limit 50 mph; everyday commuters. LOS? FFS = BFFS - fLW - fLC - fM - fA = 51.1 mph

  13. 1750 2.5 0.0 V vp = PHF N fHV fp 1.00 0.90 2 0.05 Example 1 (cont’d) = 1045 pcphpl fHV = 1/[1+PT(ET-1)+PR(ER-1)] = 0.93

  14. Example 1 (cont’d) D = vp/S = 1045/51.1 = 20.45 vpm

  15. Example 2 4-Lane rural undivided highway; V=1,500 vph; 6% trucks; 12-foot lanes; 2-foot right shoulder; 1.5% grade; 1.5 miles; 10 intersections; PHF 0.88; speed limit 50; everyday commuters. LOS?

  16. Example 2 (cont’d) D = vp/S = 877/50.8 = 17.3 vpm

  17. Example 3 A 1.5 mile section of rural divided highway is to be designed to carry a directional volume of 2,500 vph and to operate at Level of Service C. The design speed and speed limit on the roadway will be 50 mph and it will be designed with no grade and only 3 cross intersections along the entire length. Data from similar roadways indicate that 6% trucks will be present and the PHF is expected to be 0.90. If the available right-of-way is 90 feet, determine the cross section of the road to meet the design characteristics.

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