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PHILADELPHIA UNIVERSITY Faculty of Engineering. Department of Civil Engineering.

PHILADELPHIA UNIVERSITY Faculty of Engineering. Department of Civil Engineering. Transportation and Traffic Engineering Ch 3 Capacity & LOS of: Multilane Highways & Freeways 9/8/2017. 1. Multi lane Highway. Multi lane Highways. Multilane Highway.

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PHILADELPHIA UNIVERSITY Faculty of Engineering. Department of Civil Engineering.

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  1. PHILADELPHIA UNIVERSITY Faculty of Engineering. Department of Civil Engineering. Transportation and Traffic Engineering Ch 3 Capacity & LOS of: Multilane Highways & Freeways 9/8/2017 1

  2. Multi lane Highway Multi lane Highways

  3. Multilane Highway • This section is intended for analysis of uninterrupted flow rural and suburban multilane highway segments.

  4. Multilane Highway Multilane highways may exhibit some of the following characteristics: • have posted speed limits of 40 - 55 mi/h(65- 90 km/h). • They usually have a total of four or six lanes. • They may be undivided or include medians. • Multilane highways are located in suburban communities, leading into central cities, or along high-volume rural corridors connecting two cities or two activities that generate a number of daily trips.

  5. Multilane Highway • Traffic signals at major crossing points are possible. • Traffic volumes range from 15,000 to 40,000/day In some cases. • Volumes as high as 100,000 v/day have been observed. • There is partialcontrol of access. • They may include a two-way, left-turn median lane (TWLTL)

  6. Ideal conditions • For rural and suburban multilane highways Assumptions (Ideal Conditions, all other conditions reduce capacity): • Only passenger cars. • No direct access points. • A divided highway. • Speed > 60 mph ( 100 km/h ).

  7. Ideal conditions • Signal spacing > 2.0 miles. • No on-street parking. • No significant bus stops. • No significant pedestrian activities. • 12 ft (3.6m) minimum lane width and with adequate shoulders. • No lateral obstructions within 6 ft (1.8m) of the edge of the pavement.

  8. Free-Flow Speed •Free-flow speed ( FFS ) is the term used to describe the average speed that a motorist would travel if there were no congestion or other adverse conditions (such as bad weather).

  9. Measuring FFS •FFS is measured using the meanspeed of passenger cars operating in low-tomoderate flow conditions (up to 1,400 pc/h/ln). •The speed study should measure the speeds of all passenger cars or of a systematicsampling of passenger cars (e.g., of every 10th passenger car). •A sample should obtain at least 100 passenger-car speeds.

  10. Prediction of Level of Service The prediction of level of service for a multilane highway involves three steps: 1. Determination of free-flow speed 2. Adjustment of volume 3. Determination of level of service

  11. Capacity varies by FFS. Capacity is 2200, 2100, 2000 and 1900 pc/h/lane. For 100, 90, 80 and 70 km/h. respectively.

  12. Estimating Free-Flow Speed (FFS)

  13. Lane width adjustment:

  14. Lateral clearance adjustment • Fixed obstructions include light poles, signs, trees, abutments, bridge rails, traffic barriers, and retaining walls. • Standard raised curbs are not considered obstructions

  15. Lateral clearance adjustment

  16. Median Type adjustment fM: Accounts for friction between opposing directions of traffic in adjacent lanes for undivided .

  17. Access Point density adjustment The access-point density on a divided roadway is determined by dividing the total number of accesspoints ( i.e., intersections and driveways) on the right side of the roadway in the direction of travel by the segment’s total length in km. • An intersection or driveway should only be included if it influences traffic flow. fA: accounts for interruption due to access points along the facility.

  18. Calculating the Flow Rate for a Multilane Highway The flow rate in pc/h/ln for a multilane highway is computed using Eq.: where vp :15-minute passenger-car equivalent flow rate (pc/h/ln) V : hourly peak vehicle volume (veh/h) in one direction N : number of travel lanes in one direction (2 or 3) fp : driver population factor with a range of 0.85 to 1.00. Use 1.00 for commuter traffic.

  19. Heavy-Vehicle Adjustments fHV • The presence of heavy vehicles in the traffic stream decreases the FFS because base conditions allow a traffic stream of passenger cars only. • Therefore, traffic volumes must be adjusted to reflect an equivalent flow rate expressed in passenger cars per hour per lane (pc/h/ln). • This is accomplished by applying the heavy-vehicle factor (fHV).

  20. Heavy-Vehicle Adjustments fHV • Once values for ET and ER have been determined, the adjustment factor for heavy vehicles may be computed as: Where: ET, ER :passenger-car equivalents for trucks and buses and for recreational vehicles (RVs), respectively. PT, PR :proportion of trucks and buses, and RVs, respectively, in the traffic stream. (expressed as a decimal fraction). fHV :adjustment factor for heavy vehicles.

  21. Passenger-Car Equivalents Passenger-car equivalents (Ei) can be selected for 2 conditions: 1.Extended general highway segments 2.Specific grades.

  22. Extended segments method • A long multilane highway segment can be classified as an extended general highway segment • if no grade exceeding 3 percent is longer than 0.8 km,and • if grades of 3 percent or less do not exceed 1.6 km. • If the above condition is not satisfied, then specific grades should be considered (refer to the HCM2000 for details).

  23. Driver Population Factor (fp) •The adjustment factor fp reflects the effect weekend recreational and perhaps even midday drivers have on the facility. •The values for range from 0.85 to 1.00. •Typically, the analyst should select 1.00, which reflects weekday commuter traffic (i.e., users familiar with the highway), unless there is sufficient evidence that a lesser value, reflecting more recreational or weekend traffic characteristics, should be applied. fp = 1,familiar users. 1 > fp >=0.85, unfamiliar users.

  24. Calculate density Where: D: density (pc/km/In). Vp: flow rate (pc/h/In). S: average passenger-car travel speed (km/h).

  25. Cont. …

  26. Example 1 Estimate free flow speed, for a 4-lane divided highway with object located 1.2 m to the right of the travel lane, 3 m lanes width, If there are 18 access points per km ?

  27. Solution • flw = 10.6 km/h (From the table21-4). • fA =12 km/h (From the table 21-7) . • fm =0 . divided highway, (From the table21-5)

  28. BFFS : free flow under ideal conditions (100 km/h). FFS : free flow adjusted for actual conditions . FFS =100 km/h – 10.6 km/h – 0.6 km/h – 0 – 12 km/h = 76.8 km/h (reduction of 23.2 km/h )

  29. Cont. ..Example 1 • If base volume is 2,500 v/h, PHF = 0.9, N = 2, 10% heavy truck on rolling terrain, Non-familiar users, free flow speed = 76.8 km/h , Determine LOS?

  30. Solution Vp = 2500 / ( 0.9 x 2 x 0.87 x 0.85 ) = 1878 pc/h/lane.

  31. For Vp =1878 pc/hr/ln and S = 76.8 km/hr S=73.5 km/h. D = 1878 / 73.5 = 25.5 pc/h/ln. LOS is E (From the exhibit 21-2 and exhibit 21-3)

  32. Freeway 38

  33. Freeway LOS

  34. Freeway • A divided highway with full control of access and two or more lanes for the exclusive use of traffic in each direction. • A freeway is composed of three elements: basic freeway sections, weaving areas, and ramp junctions.

  35. Freeway LOS Determining FFS • Measure FFS in the field • Low to moderate traffic conditions • Use a baseline and adjust it (BFFS) Conditions of free-flow speed occur when flow rates are low to moderate (less than 1300 pc/h/ln at 70 mi/h). As flow rates increase beyond 1300, the mean speed of passenger cars in the traffic stream decreases.

  36. Base (Ideal) conditions for basic freeway segment • 12-ft lane widths (3.6 m) • 6-ft right shoulder ( 1.8 m ) • 2-ft median lateral clearance ( 0.6 m ) • Only passenger cars. • 5 or more lanes in each travel direction. • 2-mi (3 km) or greater interchange spacing • Level terrain • Mostly familiar roadway users These base conditions represent a high operating level, with a free-flow speed (FFS) of 110 km/h (70 mph) or greater.

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