1. Freeway Capacity and Level of Service
Concepts of capacity and level of service
Freeway level of service analysis procedure based on HCM

2. Capacity and Level of Service
Capacity (supply)
LOS (demand vs. supply)
Capacity and LOS analysis for different types of facilities (HCM procedures)
Freeway basic segments
Freeway ramp junctures
Freeway weaving sections
Multilane highways
Two-lane highways
Signalized intersections

3. What is capacity, what is LOS?q v u1
LOS u2 q2 q1
qmax
capacity

4. Capacity: Definition
The maximum hourly flow rate of vehicles, passengers, or the like, which can be reasonably expected to traverse a point or a section under prevailing roadway, traffic, and control conditions.

5. Key word: maximum hourly flow rate
Capacity
Key word: maximum hourly flow rate
Expected maximum handling capability determined by physical feature of the facility
Independent of demand
NOT number currently using facility (This is flow rate or volume!!)

6. Key word: prevailing conditions
Capacity
Key word: prevailing conditions
Actual conditions, not “ideal(base)” conditions
Factors that affect operation of Traffic Flow & Capacity
Traffic (volume, PHF)
Roadway(# lanes, shoulder widths, grade, etc)
Vehicle composition (Truck/Bus/RV %)
Traffic control

7. Prevailing Conditions vs. Ideal (Base) Conditions
Ideal (Base) Conditions (dependent on facility type)
12ft lanes
adequate shoulder
100% passenger cars
0% grades
minimal disturbance (from interchange, access points, etc) ……

8. Factors Affecting Capacity and LOS
Picture 1 : vehicle type, entrance,
P2: interchange and merging
P3: “mix” traffic
P4: Grade and curves
P5: vehicle type/slow moving vehicles.

9. Level of Service
Describes the QUALITY of service achieved on a transportation system in terms of…
Speed/travel time
freedom to maneuver
Traffic interruptions
Comfort
Convenience
Safety

10. Level of Service
Qualitative measure that characterizes operational conditions.
6 Levels (A – F)
A: free-flow
F: forced-flow
E: capacity A B C D E F
A: FF, B: Almost FF, C: Speed slightly lower than FF, D: appreciable slowdown. E: capacity. F: unstable

11. Highway LOS
LOS A
LOS B
LOS C

12. Highway LOS
LOS D
LOS E
LOS F

13. Service Flow Rate
Maximum flow rate of vehicles, passengers, or the like, which can be accommodated by a given facility or system under given condition AT A GIVEN LEVEL OF SERVICE (except LOS F).
Service flow rate for LOS E: capacity
e.g., If actual flow> service flow rate for LOS B & < service flow rate for LOS C
== > LOS is C

14. Highway Capacity Manual Procedures
Freeway Systems
Highways
Urban Streets
Pedestrian and Bicycles
Transit
(Now HCM 2010)

15. Freeway System Basic Segments (sections) Weaving Section
Ramp Junctions

16. Primary Measures of Effectiveness (MOEs) for LOS
Type of Facility MOE
Freeway Basic Segments Density (pcpmpl)
Freeway Weaving Areas Density
Freeway Ramp Junctions Flow Rate/Density (pcph)
Multilane Highways Density/FFS
Signalized Intersections Average Control Delay (sec/veh)
Arterials Average Travel Speed (mph)
Transit Load Factor(pers/seat, veh/h, people/hr)
Pedestrians Space (sq ft/ped)

17. Selection of Design LOS
LOS A?
No: too expensive and over design
LOS E or F?
No: too much congestion
Mostly C or sometimes D
allow some slowdowns, but no stop&go
B is desired for rural highways

18. HCM Procedure for Freeway Basic Section
Basic Section: a section beyond the influence of merging or diverging movements
The procedure is very similar to that of multilane highways

19. Ideal (Base)Conditions for Basic Freeway Section
Good weather, good visibility, no incident, no work zone, no pavement deteriration
12 ft (3.6 m) lanes
At least 6ft (1.8 m) right shoulder clearance
All passenger cars
Level terrain
Familiar driving population
Capacity (under Ideal <base> Conditions)
55 mph  2250 pcphpl
70 or 75 mph  2400 pcphpl

20. Level of Service for Basic Freeway Section
Level of Service based on traffic density in section
LOS
Density Range (pc/mi/ln=pcpmpl) A B C D E F
0-11
>11-18
>18-26
>26-35
>35-45
>45

21. Speed-flow curves and LOS (HCM 2000)

22. Speed-flow curves and LOS (HCM 2010)

23. LOS Criteria (HCM 2000)

24. LOS Criteria (HCM 2010)
Density
Maximum Service Flow rate

25. Steps for Determining LOS of Basic Freeway Segment
Step 1. Determine Free-Flow
Speed
Step 2. Determine Flow Rate
Step 3. Determine Speed using
Speed-Flow Curve
Step 4. Compute Density
Step 5. Determine Level of Service

26. Step 1. Determine FFS Field measurement
at flow<1000 (1300 in HCM 2000) pcphpl
By estimation
FFS = Estimated free-flow speed, mph.
fLW = adjustment for lane width Exhibit 11-8, mph
fLC = adjustment for right shoulder clearance Ex. 11-9, mph (no value change from HCM 2000 to HCM 2010)
TRD=total ramp density (ramps/mi), defined as the # ramps (on and off, one direction) located btw 3 mile upstream and 3 mile downstream divided by 6.

28. Same values as in Exhibit 11-9 in HCM 2010

29. Selection of FFS Interpolation not recommended
Round to nearest 5mph as follows:

30. Step 2. Determine Peak 15-min Flow Rate
vp = 15-min passenger car equivalent flow rate, pc/h/ln (pcphpl)
V = Hourly volume, veh/h (vph)
PHF = peak hour factor (typically on freeways)
N = number of lanes in one direction
fHV = heavy vehicle factor (must be computed)
fp = driver population factor (Ranges from 0.85 to 1.0)

31. Heavy Vehicle Factor ET = Passenger Equivalent for Trucks and Buses
PT = Percentage of Trucks and Buses in Traffic Stream
ER = Passenger Equivalent for Recreational Vehicles
PR = Percentage of RVs in Traffic Stream

32. Passenger Car Equivalents (No value changes)
Extended Freeway Segments Ex 11-10
Specific Upgrades
Trucks and Buses  EX 11-11
RVs  Ex 11-12
Specific Downgrades
Trucks and Buses  Ex 11-13
Depends on Grade Steepness, Length of Grade, and Percentage of Vehicles in Traffic Stream

33. HCM 2000, values same as those in Ex 11-10 in HCM 2010

34. values same as those in Ex 11-11 in HCM 2010

35. values same as those in Ex 11-12 in HCM 2010

36. values same as those in Ex 11-13 in HCM 2010

37. Step 3. Determine Speed
Estimated from the flow-speed diagram

38. Step 4. Compute Density D = Density pc/mi/ln (pcpmpl)
Vp = Peak 15-min flow rate
S = Estimated Speed

39. Step 5. Determine Level of Service
Compare computed density to values in Table
LOS
Density Range (pc/mi/ln) A B C D E F
0-11
>11-18
>18-26
>26-35
>35-45
>45

40. Step 5. Determine Level of Service
Use Figure directly (Based on flow & speed).
LOS D

41. Applications Operation Analysis Design Planning
LOS, Density, average speed
Design
# lanes
Planning
From AADT to # lanes