1. Lec 5: Capacity and Level-of-Service Analysis for Freeways, Multilane Highways & 2-Lane 2-Way Highways (p.2-60 to 2-70)
Chapter objectives: By the end of these chapters the student will be able to:
Explain why capacity is the heart of transportation issues.
Define capacity and level-of-service concept and explain why capacity is not a fixed value
Explain the relationship between the v/c ratio and level of service
Estimate (determine) the free-flow speed of a freeway or a multilane
Obtain proper passenger-car equivalents for trucks, buses, and RVs (Grade affects the performance of these vehicles)
Conduct design and planning analyses for the basic freeway and multilane highway segments (apply the knowledge of capacity and LOS to the redesign of Moark Junction.

2. Issues of traffic capacity analysis
How much traffic a given facility can accommodate?
Under what operating conditions can it accommodate that much traffic?
Highway Capacity Manual (HCM)
1950 HCM by the Bureau of Public Roads
1965 HCM by the TRB
1985 HCM by the TRB (Highway Capacity Software published)
1994 updates to 1985 HCM
1997 updates to 1994 HCM
2001 updates to 2000 HCM
2010 HCM

3. Highway Capacity Software

4. 2.4.4 The capacity concept
HCM analyses are usually for the peak (worst) 15-min period.
The capacity of a facility is:
“the maximum hourly rate at which persons or vehicles can be reasonably expected to traverse a point or uniform segment of a lane or roadway during a given time period under prevailing conditions.”
Sometimes using persons makes more sense, like transit
Some regularity expected (capacity is not a fixed value)
With different prevailing conditions, different capacity results.
Traffic
Roadway
Control

5. LOS F (worst or system breakdown)
2.4.5 Level of service
“Level of service (LOS) is a quality measure describing operational conditions within a traffic stream, generally in terms of such service measures as speed and travel time, freedom to maneuver, traffic interruptions, and comfort and convenience.”
LOS A (best)
LOS F (worst or system breakdown) A
Free flow B
Reasonably free flow C
Stable flow D
Approaching unstable flow E
Unstable flow F
Forced flow or breakdown flow
SFA
SFB
SFC
SFD
SFE
Table 2-4, p. 2-66

6. MOE in 2010 HCM Uninterrupted Fwy: Basic sections Density (pc/mi/ln)
Fwy: Weaving areas
Fwy: Ramp junctions
Multilane highways
Two-lane highways
Percent-time spent following, Average travel speed, and Percent free-flow speed
Interrupted
Signalized intersections
Approach delay (sec/veh), and v/c
Unsignalized intersections
Average total delay (sec/veh)
Arterials
Average travel speed
Transit
Load factor (pers/seat)
Pedestrians
Space (sq ft/ped)

7. The v/c ratio and its use in capacity analysis
The comparison of true demand flows to capacity is a principal objective of capacity and LOS analysis.
v/c =
Rate of flow
Capacity
The volume capacity ratio indicates the proportion of the facility’s capacity being utilized by current or projected traffic.  Used as a measure of the sufficiency of existing or proposed capacity.
v/c is usually less than or equal to 1.0. However, if a projected rate of flow is used, it may become greater than 1.0. The actual v/c cannot be greater than 1.0 if departure volume is used for v.
A v/c ratio above 1.0 predicts that the planned design facility will fail! Queue will form.

8. Freeways and multilane highways
Basic freeway segments: Segments of the freeway that are outside of the influence area of ramps or weaving areas.

9. Basic freeway and multilane highway characteristics
(This is Figure 14.2 for basic freeway segments, Roess, Prassas, and McShane).
Chapter 14

10. Equations for curves in Fig. 14.1
Table 14.1 of Roess, Prassas, McShane

11. Base Speed-Flow Curves for Multilane Highways
Fig 14.3 of Roess, Prassas, McShane

12. Base Speed-Flow Curves for Multilane Highways
Fig 14.3 of Roess, Prassas, McShane

13. 2.4.5 Level of Service LOS B LOS C or D LOS A LOS E or F Chapter 14
Table 14.2 of Roess, Prassas, McShane

14. Service flow rates and capacity
Table 14.3 and Table 14.4 of Roess, Prassas, McShane

15. Capacity and LOS analysis methodologies
Most capacity analysis models include the determination of capacity under ideal roadway, traffic, and control conditions, that is, after having taken into account adjustments for prevailing conditions.
Multilane highways
12-ft lane width, 6-ft lateral clearance, all vehicles are passenger cars, familiar drivers, free-flow speeds >= 60 mph. Divided. Zero access points. Capacity used is usually average per lane (see slide 9)
Basic freeway segments
Min. lane widths of 12 feet
Min. right-shoulder lateral clearance of 6 feet (median  2 ft)
Traffic stream consisting of passenger cars only
Ten or more lanes (in urban areas only)
Interchanges spaced every 2 miles or more
Level terrain, with grades no greater than 2%, length affects
Driver population dominated by regular and familiar users
Chapter 14

16. Prevailing condition types considered (p
Prevailing condition types considered (p.291 of Roess, Prassas, and McShane):
Lane width
Lateral clearances
Type of median (multilane highways)
Frequency of interchanges (freeways) or access points (multilane highways)
Presence of heavy vehicles in the traffic stream
Driver populations dominated by occasional or unfamiliar users of a facility

17. Factors affecting: examples
Trucks occupy more space: length and gap
Drivers shy away from concrete barriers

18. Types of analysis
Operational analysis (Determine speed and flow rate, then density and LOS)
Service flow rate and service volume analysis (for desired LOS) MSF = Max service flow rate
Design analysis (Find the number of lanes needed to serve desired MSF)

19. Service flow rates vs. service volumes
What is used for analysis is service flow rate. The actual number of vehicles that can be served during one peak hour is service volume. This reflects the peaking characteristic of traffic flow.
Stable flow
SFE
Unstable flow E F
Flow D
SVi = SFi * PHF C
SFA
Congested B A
Uncongested
Density

20. Determining the free-flow speed (1)
Free-flow speed (read carefully definitions of variables):
Basic freeway segments, eq. 14-5
Multilane highway sections, eq. 14-6
Passenger car equivalent flow rate:
BFFS:
60 mph without any data
Speed limit mph, add 7 mph
Speed limit mph, add 5 mph
Use either the graph or compute:
Then Table 14.2 for LOS.
Chapter 14
See Figure 14.4 for multilane highway sections.

21. Determining the free-flow speed (2)
Adjustment to free-flow speed on a freeway
TRD = Total number of on- and off-ramps within ±3 miles of the midpoint of the study segment, divided by 6 miles.
Chapter 14

22. Determining the free-flow speed (3)
Adjustment to free-flow speed on a multilane highway
fLW: use Table 14.5

23. Choosing a free-flow speed curve
Not recommended to interpolate. So, this table was given. This table is for both freeways and multilane highways.
Chapter 14

24. Determining the heavy-vehicle factor
PP = percent passenger cars
PT = percent trucks & buses
PR = percent recreational vehicles (RVs)
ET = PCE for trucks and buses
ER = PCE for RVs
Grade and slope length affects the values of ET and ER.
Chapter 14

25. How we deal with long, sustaining grades…
There are 3 ways to deal with long, sustaining grades: extended general freeway segments, specific upgrades, and specific downgrades.
(1) Extended segments: where no one grade of 3% or greater is longer than ¼ mi or where no one grade of less than 3% is longer than ½ mi. And for planning analysis.
Extended segments
Type of Terrain
Level
Rolling
Mountains
ET (trucks & buses)
1.5
2.5
4.5
ER (RVs)
1.2
2.0
4.0
Chapter 14

26. How we deal with long, sustaining grades…(cont)
(2) Specific upgrades: Any freeway grade of more than ½ mi for grades less than 3% or ¼ mi for grades of 3% or more. (For a composite grade, refer to page 298 right column.) Use the tables for ET and ER for specific grades.
(3) Specific downgrades:
If the downgrade is not severe enough to cause trucks to shift into low gear, treat it as a level terrain segment, ET = 1.5.
Otherwise, use the table for downgrade ET
For RVs, downgrades may be treated as level terrain, ER = 1.2.

27. Determining the driver population factor
Not well established
Between a value of 1.00 for commuters to 0.85 as a lower limit for other driver populations
Usually 1.00
If there are many unfamiliar drivers use a value between 1.00 and 0.85
For a future situation 0.85 is suggested

28. Planning analysis Step 1: Find fHV using for ET and ER.
You want to find out how many lanes are needed for the targeted level of service.
Step 1: Find fHV using for ET and ER.
Step 2: Try 2 lanes in each direction, unless it is obvious that more lanes will be needed.
Step 3: Convert volume (vph) to flow rate (pcphpl), vp, for the current number of lanes in each direction.
Step 4: If vp exceeds capacity, add one lane in each direction and return to Step 2.
Step 5: Compute FFS.
Step 6: Determine the LOS for the freeway with the current number of lanes being considered. If the LOS is not good enough, add another lane and return to Step 3.

29. Determining the driver population factor
Not well established
Between a value of 1.00 for commuters to 0.85 as a lower limit for other driver populations
Usually 1.00
If there are many unfamiliar drivers use a value between 1.00 and 0.85
For a future situation 0.85 is suggested

30. Lec 6: Two-Lane Highway: Classes
Class I highways: generally arterial highways that serve long-distance trips and on which motorists expect to travel at high speeds.
Class II highways: highways that serve shorter trips and on which motorists do not expect to travel at high speeds.
Class III highwqays: serve more developed areas

31. Two-Lane Highway: Design Standards & LOS
ATS = Average Travel Speed: Average speed of all vehicles traversing the defined analysis segment for the specified time period (peak 15 minutes)
PTSF = Percent Time Spent Following: Aggregate percentage of time that all drivers spend in queues, unable to pass, with the speed restricted by the queue leader. A surrogate measure for PTSF is the percentage of vehicles following others at headways of 3.0 seconds or less.
PFFS = Percent Free-Flow Speed: is based on the cmparisonof the prevailing speed to the free-flow speed, expressed in percentage.
Table 16-1 and Table 16-4 from Roess, Prassas, and McShane 4th edition.

32. Design Level of Service
Table 2-5 of GB2011, page 2-67.

33. AADT at the Moark Junction (2011)

34. ATR locations

35. 2009 data Hour Begin US 6 EB US 6 WB US 6 Total EB/Total %
US 6: % of ADT
US89 SB
US 89: % of ADT
0:00
68.0
63.7
131.7
51.6%
1.11%
6.3
0.60%
1:00
52.3
104.6
50.0%
0.88% 1
0.10%
2:00
49.0
38.7
87.7
55.9%
0.74%
0.7
0.07%
3:00
48.7
33.3
82.0
59.4%
0.69%
4:00
53.3
41.0
94.3
56.5%
0.79%
4.3
0.41%
5:00
142.3
75.3
217.6
65.4%
1.83%
26.7
2.55%
6:00
329.0
156.3
485.3
67.8%
4.09%
29.3
2.79%
7:00
407.3
176.0
583.3
69.8%
4.91% 43
4.10%
8:00
510.0
231.4
741.4
68.8%
6.24% 61
5.82%
9:00
505.7
310.3
816.0
62.0%
6.87% 64
6.10%
10:00
494.0
299.5
793.5
62.3%
6.68%
57.2
5.45%
11:00
479.3
244.0
723.3
66.3%
6.09%
12:00
480.3
220.3
700.6
68.6%
5.90%
61.5
5.86%
13:00
444.0
259.4
703.4
63.1%
5.92%
66.5
6.34%
14:00
486.0
272.7
758.7
64.1%
6.39% 68
6.48%
15:00
462.7
330.7
793.4
58.3% 91
8.68%
16:00
465.7
283.7
749.4
62.1%
6.31%
78.7
7.50%
17:00
425.7
253.3
679.0
62.7%
5.72%
86.3
8.23%
18:00
403.7
275.0
678.7
59.5%
70.3
6.70%
19:00
218.3
549.0
60.2%
4.62%
56.3
5.37%
20:00
259.7
219.3
479.0
54.2%
4.03%
50.3
4.80%
21:00
216.0
181.3
397.3
54.4%
3.35% 31
2.96%
22:00
159.7
147.3
307.0
52.0%
2.59%
17.3
1.65%
23:00
107.0
111.7
218.7
48.9%
1.84%
13.3
1.27%
Total
7380.1
4494.8
1048.7
2009 data

36. Moark Junction Traffic Distribution
Hourly volumes at ATRs of UDOT can be found at:
How many lanes do these routes need?