Lecture 4: Capacity and Level of Service (LoS) of Freeways Basic Segments. Prof. Responsável: Filipe Moura

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1 Lecture 4: Capacity and Level of Service (LoS) of Freeways Basic Segments Prof. Responsável: Filipe Moura Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 1

2 CAPACITY AND LEVEL OF SERVICE (LOS) CAPACITY The maximum sustainable flow rate at which vehicles or persons reasonably can be expected to traverse a point or uniform segment of a lane or roadway during a specified time period under given roadway, geometric, traffic, environmental, and control conditions; usually expressed as vehicles per hour, passenger cars per hour, or persons per hour. On ideal conditions in one freeway = 2400 veh/h/ln LEVEL OF SERVICE A qualitative measure describing operational conditions within a traffic stream, based on service measures such as speed and travel time, freedom to maneuver, traffic interruptions, comfort, and convenience. Speed restrictions associated with LOS LOS A - Rare LOS B - Sporadic LOS C - Frequent LOS D - Sistematic LOS E - Permanent LOS F Discontinuous flow Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 2

3 D = v p s Level of Service (LOS) from A to F

4 Factors influencing Capacity and LOS The concepts of Level of service and Capacity are in general applicable to all transport modes, including pedestrians For different types of facilities there are different procedures and methodologies for calculating Capacity and indicators of LOS In road traffic, the variables (perceived by drivers) which are the most closely related with level of service are: Density Percentage of time spent following Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 4

Freeway definition Source: A1, North Yorkshire, UK (www.freefoto.

5 Freeway definition Source: A1, North Yorkshire, UK ( A freeway could be defined as: A multilane, divided highway with a minimum of two lanes for the exclusive use of traffic in each direction and full control of access without traffic interruption Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 5

2-Lane Highway definition Source: http://www.caption-this.com/carpassing.

6 2-Lane Highway definition Source: A 2-lane highway could be defined as: A roadway with a two-lane cross section, one lane for each direction of flow, on which passing maneuvers must be made in the opposing lane. Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 6

where the crossing of two or more traffic streams traveling in the same direction occurs (Ramps) (Basic segment) (Ramp Off) (Ramp

7 Freeway segments There are three different types of freeway segments: Basic freeway segments traffic conditions are not affected by vehicles entering or leaving the freeway Ramps freeway segments with exit or entering ramps Weaving segments freeway segments where the crossing of two or more traffic streams traveling in the same direction occurs (Ramps) (Basic segment) (Ramp Off) (Ramp On) (Weaving) (Basic segment) (Basic segment) (Ramp On) (Ramp Off) Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 7

8 Access Ramps in one Freeway Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 8

9 Main concepts for Basic Freeway segments (I) Capacity: Defined for each direction and measured for 15 minutes period. It is expressed in private car (equivalent units) per hour and lane. Speed-flow-density relationship Depends on prevailing traffic and roadway conditions Base case of capacity calculation assumes the following ideal conditions : Minimum lane widths of 3.6 m; Minimum right-shoulder lateral clearance between the edge of the travel lane and the nearest obstacle or object that influences traffic behavior of 1.8 m; Minimum median left-shoulder lateral clearance of 0.6 m; Traffic stream composed entirely of passenger cars; Five or more lanes for one direction (in urban areas only); Interchange distance of 3 km or greater (interchange density in HCM); Level terrain, with grades no greater than 2 percent; and A driver population composed principally of regular users of the facility. These base conditions represent a high operating level, with a free-flow speed (FFS) of 110 km/h or greater. Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 9

and lateral clearance on lateral placement of vehicles

10 Lateral clearance effect Base conditions with respect to lane width and lateral clearance Influence of lane width and lateral clearance on lateral placement of vehicles Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 10

Main concepts for Basic Freeway segments (II) Capacity in a freeway segment: With ideal geometrical and traffic conditions Ø Could reach 2400 pc/h/lane @ FFS=120km/h; D = 20 v/km (45m distance)

11 Main concepts for Basic Freeway segments (II) Capacity in a freeway segment: With ideal geometrical and traffic conditions Ø Could reach 2400 FFS=120km/h; D = 20 v/km (45m distance) Diminishing FFS induces a reduction of capacity Ø Could reach 2250 pc/h/lane@ FFS = 90 km/h; D = 25 v/km (35m distance) Free Flow Speed (FFS): Theoretically, speed when density is null; In reality, it is the average speed when density is very low (in practice the vehicles don t influence each other speeds) Speed S FFS Free-flow speed 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). FFS depends on the physical characteristics of the infrastructure 0 Dj Kj Density Densidade Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 11

12 Level of Service (LoS) (I) Level of Service in a Freeway segment: The measure used to provide an estimate of level of service is density. This is the parameter that reflects the influences between vehicles Density can be obtained by the following equation : D = v p s Where D is density [veh/km] V p is the flow in private car equivalent units [pcu/h] S is average speed [km/h] Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 12

13 Level of Service (LOS) (II) Source: (TRB, 2000) Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 13

14 Density- Flow relationship Relation Density Flow in a freeway segment Source: (TRB, 2000, Exhibit 13.3) Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 14

15 LOS criteria for basic freeway segments Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 15

16 Determine Level of Service (I) 1. Calculate free flow speed (FFS), from which the speed flow curve (SFC) is deduced 2. Estimate flow rate and speed either using the SFC curve (or by analytical calculation) 3. Compute density using flow rate and speed 4. Determine LOS from values of density Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 16

Determine Level of Service (II) Physical

grade and type of terrain % of trucks and

5) f LC (pg.23.6) f ID (pg.23.7) Et (pg.23.10) Pt (pg.

23.11) FFS = BFFS f LW f LC f N f ID v P =

17 Determine Level of Service (II) Physical attributes of the freeway segment Traffic attributes Lane Width Lateral clearance Interchange density Number of Lanes Road grade and type of terrain % of trucks and buses PHF Driver population f LW (pg.23.5) f LC (pg.23.6) f ID (pg.23.7) Et (pg.23.10) Pt (pg.23.11) f N (pg.23.6) N f HV (pg.23.8) f P (pg.23.11) FFS = BFFS f LW f LC f N f ID v P = v PHF N f HV f P S (pg.23.4) D (pg.23.12) LOS (pg.23.3) Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 17

18 1 st Step compute the Free Flow Speed FFS could be estimated through on site observations providing that the flow is less than 1300 pc/h/lane (otherwise drivers will start imposing constraints on each other). When it is not possible to measure FFS on site, it can be computed through adjustments on Base-Free Flow Speed (BFFS). (FFS) When there is no other information on the BFFS of the freeway segment you are analyzing, you should consider 120 km/h in rural (inter-urban) freeways and 100 km/h in urban or suburban freeways. where: FFS = BFFS - f LW f LC f N - f ID f LW = adjustment factor for lane width f LC = adjustment factor for lateral clearance (right shoulder lateral clearance) f N = adjustment factor for number of lanes f ID = adjustment factor for interchange density (at least one on-ramp over 10km) Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 18

19 Lane width (f LW ) Lateral clearance (f LC ) Right-Shoulder Lateral Clearance (m) Lane Width (m) EXHIBIT ADJUSTMENTS FOR LANE WIDTH Reduction in Free-Flow Speed, f LW (km/h) EXHIBIT ADJUSTMENTS FOR RIGHT-SHOULDER LATERAL CLEARANCE Reduction in Free-Flow Speed, f LC (km/h) Lanes in One Direction Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 19

20 Number of Lanes (f N ) Interchange Density (f ID ) EXHIBIT ADJUSTMENTS FOR NUMBER OF LANES Number of Lanes (One Direction) Note: For all rural freeway segments, f N is 0.0. Reduction in Free-Flow Speed, f N (km/h) EXHIBIT ADJUSTMENTS FOR INTERCHANGE DENSITY Interchanges per Kilometer Reduction in Free-Flow Speed, f ID (km/h) Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 20

N f HV f p It is calculated for ONE LANE equivalent!

21 2 nd Step - Estimation of flow rate (V p ) The computation of V p reflects the peak 15 min period in the peak hour. It is expressed in pc/h/ln. It is influenced by: f HV - Traffic composition (determined by the % of heavy vehicles in the traffic flow) f P - Type of drivers (determined by the % of commuters) v p = V PHF N f HV f p It is calculated for ONE LANE equivalent! With V = total hourly traffic volume (vehicles/hour) PHF = Peak Hour factor Ø typically between 0,8 and 0,95 in urban areas and lower for interurban freeways N = number of lanes per direction f HV = heavy vehicles adjustment factor f p = driver population factor Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 21

22 Heavy vehicle adjustment (f HV ) Heavy vehicles are mainly composed by trucks, buses and Recreational Vehicles (RV s) Trucks are the majority of such vehicles in a traffic flow and as such the most important aspect to take into consideration. f HV = 1+ P T ( E T 1 1) + P R ( E R 1) ü P T is the percentage of trucks/buses in the traffic flow ü P R the percentage of recreational vehicles (caravans); ü E T and E R are conversion factors to obtain passenger-car equivalents, which vary according to different orographic conditions Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 22

23 Grades in extended freeway segments (I) The effect of HV depends on the grades of the freeway segment and is reflected in the pcequivalents in this methodology. Three types of segments are considered: Extended freeway segments Upgrades and Downgrades It is often appropriate to consider an extended length of freeway containing a number of upgrades, downgrades, and level segments as a single uniform segment. This is done where no one grade is long enough or steep enough to have a significant effect on the operation of the overall segment. Extended freeway segments could de classified as: Level terrain Rolling terrain Mountainous terrain However, if i < 3% and L 1.0 km or i 3% and L < 0.5 km then the segment must be analyzed separately because of its significant effect on traffic flow. Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 23

24 Grades in extended freeway segments (II) Level Terrain Ø is any combination of grades and horizontal or vertical alignment that permits heavy vehicles to maintain the same speed as passenger cars. This type of terrain includes short grades of no more than 2 percent. Rolling Terrain Ø is any combination of grades and horizontal or vertical alignment that causes heavy vehicles to reduce their speeds substantially below those of passenger cars but that does not cause heavy vehicles to operate at crawl speeds for any significant length of time or at frequent intervals. Mountainous Terrain Ø is any combination of grades and horizontal or vertical alignment that causes heavy vehicles to operate at crawl speeds for significant distances or at frequent intervals. E T (trucks and buses) E R (RVs) EXHIBIT PASSENGER-CAR EQUIVALENTS ON EXTENDED FREEWAY SEGMENTS Type of Terrain Factor Level Rolling Mountainous Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 24

25 Specific grades in freeway segments Freeway segments which doesn't obey the conditions described earlier are considered specific upgrades In specific upgrades Length (km) and grade (%) both influence E T The percentage of heavy vehicles (P T ) also influences E T because they tend to group in platoons In downgrades, the heavy vehicles effect is calculated as in level terrain except when: L > 6,4 km and i > 4%, where specific downgrades parameters should be used. Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 25

26 Grades in freeways (upgrades) EXHIBIT PASSENGER-CAR EQUIVALENTS FOR TRUCKS AND BUSES ON UPGRADES E T Upgrade Length Percentage of Trucks and Buses (%) (km) < 2 All > > > > > > > 3 4 > > > > > > 4 5 > > > > > 5 6 > > > > > > 6 > > > > Trucks and Buses Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 26

27 Grades in freeways (upgrades) Recreational Vehicles - RVs Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 27

28 Grades in freeways (downgrades) Trucks and Buses EXHIBIT PASSENGER-CAR EQUIVALENTS FOR TRUCKS AND BUSES ON DOWNGRADES E T Downgrade Length Percentage of Trucks < > 5 6 > 5 6 > 6 > 6 (%) (km) All 6.4 > > > Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 28

29 Composite Grades (I) In a basic freeway segment analysis, an overall average grade can substitute a series of grades if no single portion of the grade is steeper than 4% or the total length of the grade is less than 1200m. For grades outside these limits (i.e., grades having either a total length greater than 1200 m or portions steeper than 4%, or both), the composite grade procedure is recommended. The composite grade procedure is used to determine an equivalent grade that will result in the same final truck speed as would a series of varying grades. Ø If both consecutive ramps have i<4% or L total <1200 m: Weighted average (based on each segments s lenght) should be used for grade. Ø For successive grades outside these limits (i>4% and/or L total >1200 m) It is necessary to find an equivalent grade evaluating the impact of each ramp in the speed of heavy vehicles using the following abacus Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 29

30 Composite Grades (II) Speed (km/h) EXHIBIT A23-2. PERFORMANCE CURVES FOR TRUCKS (120 kg/kw) -5% -4% -3% -2% -1% 0% Acceleration Deceleration 1% 2% 3% 4% 5% 6% 7% 8% Length in Hundreds of Meters Source: (TRB, 2000, Exhibit A23.2) Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 30

31 Composite Grades (III) Speed (km/h) EXHIBIT A23-2. PERFORMANCE CURVES FOR TRUCKS (120 kg/kw) -5% -4% -3% -2% -1% 0% Acceleration Deceleration Length in Hundreds of Meters Example: 1 st Segment is 1500m long with 2% upgrade; 2 nd segment is 1500m long with 6% upgrade What is the final grade equivalent to the composite effect of both segments on the HV speed? Answer: 6%. Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments % 2% 3% 4% 5% 6% 7% 8% 8

32 Driver Population (f P ) It is generally accepted that traffic streams composed of different types of drivers (e.g., commuters and recreational drivers) use freeways less efficiently. The adjustment factor fp is used to reflect this effect. ü The values of fp range from 0.85 to In general, the analyst should select 1.00, which reflects commuter traffic (i.e., familiar users), unless there is sufficient evidence that a lower value should be applied Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 32

33 a) Through speed flow curves as a function of FFS 3 rd Step estimating average passenger car speed Average Passenger-Car Speed, S (km/h) EXHIBIT SPEED-FLOW CURVES AND LOS FOR BASIC FREEWAY SEGMENTS Free-Flow Speed, FFS = 120 km/h km/h km/h km/h 1750 LOS A B C D E Density = 7 pc/km/ln 11 pc/km/ln 16 pc/km/ln 22 pc/km/ln 28 pc/km/ln Note: Flow Rate, v p (pc/h/ln) Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 33

34 3 rd Step estimating average passenger car speed b. Through analytical computation If FFS is between 90 and 120 km/h, average speed (s) could be given by the following equations : 1. If ( FFS) < Vp < ( FFS), then FFS- s = 1 28 ( 23FFS-1800) vp + 15FFS FFS If Vp < ( FFS) then s = FFS Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 34

35 3 rd Step estimating average passenger car speed c. Through analytical computation Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 35

36 4 th Step determining LOS DENSITY: where D is density [pc/km/ln] V p flow rate [pc/h/ln] D = S average passenger car speed [km/h] LEVEL OF SERVICE: According density based on the values of this table v p s Density (pc/km/lane) LOS 0 7 A > 7 11 B > C > D > E > 28 F Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 36

37 Methodology limitations The methodology does not apply to or take into account (without modification by the analyst) the following: Special lanes reserved for a single vehicle type, such as high-occupancy vehicle (HOV) lanes, truck lanes, and climbing lanes; Extended bridge and tunnel segments; Segments near a toll plaza; Facilities with free-flow speeds below 90 km/h or in excess of 120 km/h; Demand conditions in excess of capacity (refer to Chapter 22 for further discussion); The influence of downstream blockages or queuing on a segment; Posted speed limit, the extent of police enforcement, or the presence of intelligent transportation systems features related to vehicle or driver guidance; or Capacity-enhancing effects of ramp metering. Engenharia de Tráfego Rodoviário Lecture 4 - Basic Freeway segments 37

JCE 4600 Basic Freeway Segments

JCE 4600 Basic Freeway Segments HCM Applications What is a Freeway? divided highway with full control of access two or more lanes for the exclusive use of traffic in each direction no signalized or stop-controlled