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Transportation Engineering
Lina Shbeeb
Capacity Analysis
Traffic flow theory in practice
 Used in facility planning
 The understanding of facility capacity
 Used in design
 Th...
Applications of Traffic Flow Theory
 Determining turning lane lengths
 Average delay at intersections
 Average delay at...
Various Types of Traffic Volumes
 DailyVolume
 AverageAnnual DailyTraffic (AADT)
 AverageAnnualWeekdayTraffic (AAWT)
 ...
AADT and AAWT
 AverageAnnual DailyTraffic (AADT)
 Average 24-hour traffic volume at a location over a full 365-day
year,...
ADT and AWT
 Average DailyTraffic (ADT)
 Average 24-hour traffic at a location for any period less than a
year (e.g. six...
DDHV/PHV
 Directional Design Hourly volume (DDHV) ~ Peak
HourlyVolume
DDHV (veh/hour) =AADT x K x D
where AADT = Average ...
DDHV/PHV
 For design purposes, K factor is generally chosen as 30 HV and D
factor as the percentage of traffic in predomi...
Sub-Hourly Volume
 Sub-hourlyVolume ~ 15-minVolume
Suppose, the peak 15-min volume observed = 750 veh
So, the HourlyVolum...
Peak Hour Factor
 Relationship between hourly volume and maximum
rate of flow within the hour
For intersection:
PHF = =
w...
Example of PHF Calculation
 Data collected are as follows:
Time Interval Volume (veh)
4:00-4:15 pm 950
4:15-4:30 pm 1100
...
Example of PHF Calculation
We find from the table,
HV = 4300 veh/hour
V15 = 1200 veh
Therefore,
PHF = = = 0.90
HV
4 x V15
...
Peak Hour Factor
For freeway/expressway:
PHF =
where HV = Hourly volume (veh/hour)
V5 = max. 5-min volume within the hour ...
Traffic Volume
 Number of vehicles passing a given point or a section of a
roadway during a specified time
 Data collect...
Relationship of Highest Hourly Volume and
ADT on Rural Arterials
Travel Time and Delay Surveys
 Want to determine travel time between two points or causes of
delay along a route
 Used f...
Stream measurements: the moving
observer method
 Moving Observer
 stopwatch, pen and paper
 laptop PC
 instrumented ve...
Travel Time
By travelling several times in a car fromA to B, a
person notes down the time taken in each run and
then comes...
Delay
Delay =Actual travel time - Expected travel time
 Stopped time delay
 Travel time delay
Calculation of Delay
 Travel time delay
 Actual travel time data collected by traveling in a car through
the stretch of ...
Introduction
 Shock wave - a rapid change in traffic conditions (speed,
density, and flow)
 A moving boundary between tw...
Travel Time
By travelling several times in a car fromA to B, a
person notes down the time taken in each run and
then comes...
Delay
Delay =Actual travel time - Expected travel time
 Stopped time delay
 Travel time delay
Calculation of Delay
 Travel time delay
 Actual travel time data collected by traveling in a car through
the stretch of ...
Level of Service (LOS)
25
 Concept – a qualitative measure describing operational
conditions within a traffic stream and ...
LOS A (Freeway)
 Free flow conditions
 Vehicles are unimpeded in
their ability to maneuver
within the traffic stream
 I...
LOS B
 Flow reasonably free
 Ability to maneuver is
slightly restricted
 General level of physical and
psychological co...
LOS C
 Flow at or near FFS
 Freedom to maneuver is
noticeably restricted
 Lane changes more difficult
 Minor incidents...
LOS D
 Speeds begin to decline with
increasing flow
 Freedom to maneuver is
noticeably limited
 Drivers experience phys...
LOS E
 Capacity
 Operations are volatile, virtually
no usable gaps
 Vehicles are closely spaced
 Disruptions such as l...
LOS F
 Breakdown or forced flow
 Occurs when:
 Traffic incidents cause a
temporary reduction in capacity
 At points of...
Design Level of Service
32
This is the desired quality of traffic conditions from a driver’s
perspective (used to determin...
Design Level of Service (LOS)
33
Capacity – Defined
34
 Capacity: Maximum hourly rate of vehicles or
persons that can reasonably be expected to pass a poi...
Ideal Capacity
35
 Freeways: Capacity (Free-
Flow Speed)
2,400 pcphpl (70 mph)
2,350 pcphpl (65 mph)
2,300 pcphpl (60 mph...
Principles for Acceptable Degree of
Congestion:
36
1. Demand <= capacity, even for short time
2. 75-85% of capacity at sig...
Multilane Highways
37
 Chapter 21 of the Highway Capacity Manual
 For rural and suburban multilane highways
 Assumption...
Multilane Highways
38
 Intended for analysis of uninterrupted-flow highway
segments
 Signal spacing > 2.0 miles
 No on-...
39
Source: HCM, 2000
40
Source: HCM, 2000
Step 1: Gather data
Step 2: Calculate capacity
(Supply)
41
Source: HCM, 2000
42
Source: HCM, 2000
Lane Width
43
 Base Conditions: 12 foot lanes
Source: HCM, 2000
Lane Width (Example)
44
Source: HCM, 2000
How much does use of 10-foot lanes decrease
free flow speed?
Flw = 6.6 mph
Lateral Clearance
45
 Distance to fixed objects
 Assumes
 >= 6 feet from right edge of travel lanes to obstruction
 >=...
Lateral Clearance
46
TLC = LCR + LCL
TLC = total lateral clearance in feet
LCR = lateral clearance from right edge of trav...
47
Source: HCM, 2000
48
Example: Calculate lateral clearance adjustment for a 4-lane
divided highway with milepost markers located 4 feet to th...
49
fm: Accounts for friction between opposing directions of
traffic in adjacent lanes for undivided
No adjustment for divi...
50
Fa accounts for interruption due to access points along
the facility
Example: if there are 20 access points per mile, w...
Estimate Free flow Speed
51
BFFS = free flow under ideal conditions
FFS = free flow adjusted for actual conditions
From pr...
52
Source: HCM, 2000
Step 3: Estimate
demand
53
Calculate Flow Rate
Heavy Vehicle Adjustment
54
 Heavy vehicles affect traffic
 Slower, larger
 fhv increases number of passenger vehicles ...
f(hv) General Grade Definitions:
55
 Level: combination of alignment (horizontal and vertical) that
allows heavy vehicles...
56
Example: for 10% heavy trucks on rolling
terrain, what is Fhv?
For rolling terrain, ET = 2.5
Fhv = _________1_______ = ...
Driver Population Factor (fp)
57
 Non-familiar users affect capacity
 fp = 1, familiar users
 1 > fp >=0.85, unfamiliar...
58
Source: HCM, 2000
Step 4: Determine
LOS
Demand Vs.
Supply
59
 Calculate vp
 Example: base volume is 2,500 veh/hour
 PHF = 0.9, N = 2
 fhv from previous, fhv = 0.87
 Non-famili...
Calculate Density
60
Example: for previous
D = _____1878 vph____ = 39.1 pc/mi/lane
48 mph
61
LOS = E
Also, D = 39.1 pc/mi/ln, LOS E
Design Decision
62
 What can we change in a design to provide an acceptable
LOS?
 Lateral clearance (only 0.4 mph)
 Lan...
Lane Width (Example)
63
Source: HCM, 2000
How much does use of 10 foot lanes decrease free
flow speed?
Flw = 6.6 mph
Recalculate Density
64
Example: for previous (but with wider lanes)
D = _____1878 vph____ = 34.1 pc/mi/lane
55 mph
65
LOS = E
Now D = 34.1 pc/mi/ln, on border of LOS E
66
 Recalculate vp, while adding a lane
 Example: base volume is 2,500 veh/hour
 PHF = 0.9, N = 3
 fhv from previous, ...
Calculate Density
67
Example: for previous
D = _____1252 vph____ = 26.1 pc/mi/lane
48 mph
68
LOS = D
Now D = 26.1 pc/mi/ln, LOS D (almost C)
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Lec 12 Capacity Analysis (Transportation Engineering Dr.Lina Shbeeb)

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Lec 12 Capacity Analysis (Transportation Engineering Dr.Lina Shbeeb)

  1. 1. Transportation Engineering Lina Shbeeb Capacity Analysis
  2. 2. Traffic flow theory in practice  Used in facility planning  The understanding of facility capacity  Used in design  The sizing and geometric features of facilities  Used in performance measure  The level of service offered by a specific facility  Delay  Travel speeds  Travel times
  3. 3. Applications of Traffic Flow Theory  Determining turning lane lengths  Average delay at intersections  Average delay at freeway ramp merging areas  Change in the levels of freeway performance  Simulation (mathematical models (algorithms) to study interrelationship among the different elements of traffic itcdemo3d.ram
  4. 4. Various Types of Traffic Volumes  DailyVolume  AverageAnnual DailyTraffic (AADT)  AverageAnnualWeekdayTraffic (AAWT)  Average DailyTraffic (ADT)  AverageWeekdayTraffic (AWT)  HourlyVolume  SubhourlyVolume
  5. 5. AADT and AAWT  AverageAnnual DailyTraffic (AADT)  Average 24-hour traffic volume at a location over a full 365-day year, which is the total number of vehicles passing the location divided by 365  AverageAnnualWeekdayTraffic (AAWT)  Average 24-hour traffic volume on weekdays over a full year, which is the total weekday traffic volume divided by 260
  6. 6. ADT and AWT  Average DailyTraffic (ADT)  Average 24-hour traffic at a location for any period less than a year (e.g. six months, a season, a month, a week or even two days)  AverageWeekdayTraffic (AWT)  Average 24-hour traffic volume on weekdays for any period less than a year
  7. 7. DDHV/PHV  Directional Design Hourly volume (DDHV) ~ Peak HourlyVolume DDHV (veh/hour) =AADT x K x D where AADT = Average Annual DailyTraffic (veh/day) K = Proportion of daily traffic occurring in peak hour (decimal) D = Proportion of peak hour traffic traveling in the peak direction (decimal) Contd…
  8. 8. DDHV/PHV  For design purposes, K factor is generally chosen as 30 HV and D factor as the percentage of traffic in predominant direction during the design hour  General ranges for K and D factors Facility Type K Factor D Factor Rural 0.15 – 0.25 0.65 – 0.80 Suburban 0.12 – 0.15 0.55 – 0.65 Urban 0.07 – 0.12 0.50 – 0.60
  9. 9. Sub-Hourly Volume  Sub-hourlyVolume ~ 15-minVolume Suppose, the peak 15-min volume observed = 750 veh So, the HourlyVolume = 15-min volume x 4 = 750 x 4 = 3000 veh/hour
  10. 10. Peak Hour Factor  Relationship between hourly volume and maximum rate of flow within the hour For intersection: PHF = = where HV = Hourly volume (veh/hour) V15 = max. 15-min volume within the hour (veh) Hourly Volume Max. Rate of Flow HV 4 x V15
  11. 11. Example of PHF Calculation  Data collected are as follows: Time Interval Volume (veh) 4:00-4:15 pm 950 4:15-4:30 pm 1100 4:30-4:45 pm 1200 4:45-5:00 pm 1050 Hourly Volume 4300
  12. 12. Example of PHF Calculation We find from the table, HV = 4300 veh/hour V15 = 1200 veh Therefore, PHF = = = 0.90 HV 4 x V15 4300 4 x 1200
  13. 13. Peak Hour Factor For freeway/expressway: PHF = where HV = Hourly volume (veh/hour) V5 = max. 5-min volume within the hour (veh) HV 12 x V5
  14. 14. Traffic Volume  Number of vehicles passing a given point or a section of a roadway during a specified time  Data collected by  Manual counting  Electro-mechanical devices
  15. 15. Relationship of Highest Hourly Volume and ADT on Rural Arterials
  16. 16. Travel Time and Delay Surveys  Want to determine travel time between two points or causes of delay along a route  Used for Performance monitoring Before and after evaluation of traffic management schemes or new infrastructure
  17. 17. Stream measurements: the moving observer method  Moving Observer  stopwatch, pen and paper  laptop PC  instrumented vehicle => Chase car versus floating car techniques  Stationary Observer  number plate survey  Field staff or optical character recognition from video  Vehicle electronic tags  Mobile phone
  18. 18. Travel Time By travelling several times in a car fromA to B, a person notes down the time taken in each run and then comes up with a statistical average ofTravel Time. A B
  19. 19. Delay Delay =Actual travel time - Expected travel time  Stopped time delay  Travel time delay
  20. 20. Calculation of Delay  Travel time delay  Actual travel time data collected by traveling in a car through the stretch of the road under study.  Expected travel time calculated from the distance and average speed.  Travel time delay calculated from the difference between actual travel time and expected travel time.  Stopped time data for the vehicular speed of 0 to 5 mph.
  21. 21. Introduction  Shock wave - a rapid change in traffic conditions (speed, density, and flow)  A moving boundary between two different traffic states  Forward, backward, and stationary shock waves
  22. 22. Travel Time By travelling several times in a car fromA to B, a person notes down the time taken in each run and then comes up with a statistical average ofTravel Time. A B
  23. 23. Delay Delay =Actual travel time - Expected travel time  Stopped time delay  Travel time delay
  24. 24. Calculation of Delay  Travel time delay  Actual travel time data collected by traveling in a car through the stretch of the road under study.  Expected travel time calculated from the distance and average speed.  Travel time delay calculated from the difference between actual travel time and expected travel time.  Stopped time data for the vehicular speed of 0 to 5 mph.
  25. 25. Level of Service (LOS) 25  Concept – a qualitative measure describing operational conditions within a traffic stream and their perception by drivers and/or passengers  Levels represent range of operating conditions defined by measures of effectiveness (MOE)
  26. 26. LOS A (Freeway)  Free flow conditions  Vehicles are unimpeded in their ability to maneuver within the traffic stream  Incidents and breakdowns are easily absorbed 26
  27. 27. LOS B  Flow reasonably free  Ability to maneuver is slightly restricted  General level of physical and psychological comfort provided to drivers is high  Effects of incidents and breakdowns are easily absorbed 27
  28. 28. LOS C  Flow at or near FFS  Freedom to maneuver is noticeably restricted  Lane changes more difficult  Minor incidents will be absorbed, but will cause deterioration in service  Queues may form behind significant blockage 28
  29. 29. LOS D  Speeds begin to decline with increasing flow  Freedom to maneuver is noticeably limited  Drivers experience physical and psychological discomfort  Even minor incidents cause queuing, traffic stream cannot absorb disruptions 29
  30. 30. LOS E  Capacity  Operations are volatile, virtually no usable gaps  Vehicles are closely spaced  Disruptions such as lane changes can cause a disruption wave that propagates throughout the upstream traffic flow  Cannot dissipate even minor disruptions, incidents will cause breakdown 30
  31. 31. LOS F  Breakdown or forced flow  Occurs when:  Traffic incidents cause a temporary reduction in capacity  At points of recurring congestion, such as merge or weaving segments  In forecast situations, projected flow (demand) exceeds estimated capacity 31
  32. 32. Design Level of Service 32 This is the desired quality of traffic conditions from a driver’s perspective (used to determine number of lanes)  Design LOS is higher for higher functional classes  Design LOS is higher for rural areas  LOS is higher for level/rolling than mountainous terrain  Other factors include: adjacent land use type and development intensity, environmental factors, and aesthetic and historic values  Design all elements to same LOS (use HCM to analyze)
  33. 33. Design Level of Service (LOS) 33
  34. 34. Capacity – Defined 34  Capacity: Maximum hourly rate of vehicles or persons that can reasonably be expected to pass a point, or traverse a uniform section of lane or roadway, during a specified time period under prevailing conditions (traffic and roadway)  Different for different facilities (freeway, multilane, 2- lane rural, signals)  Why would it be different?
  35. 35. Ideal Capacity 35  Freeways: Capacity (Free- Flow Speed) 2,400 pcphpl (70 mph) 2,350 pcphpl (65 mph) 2,300 pcphpl (60 mph) 2,250 pcphpl (55 mph)  Multilane Suburban/Rural 2,200 pcphpl (60 mph) 2,100 (55 mph) 2,000 (50 mph) 1,900 (45 mph)  2-lane rural – 2,800 pcph  Signal – 1,900 pcphgpl
  36. 36. Principles for Acceptable Degree of Congestion: 36 1. Demand <= capacity, even for short time 2. 75-85% of capacity at signals 3. Dissipate from queue @ 1500-1800 vph 4. Afford some choice of speed, related to trip length 5. Freedom from tension, esp long trips, < 42 veh/mi. 6. Practical limits - users expect lower LOS in expensive situations (urban, mountainous)
  37. 37. Multilane Highways 37  Chapter 21 of the Highway Capacity Manual  For rural and suburban multilane highways  Assumptions (Ideal Conditions, all other conditions reduce capacity):  Only passenger cars  No direct access points  A divided highway  FFS > 60 mph  Represents highest level of multilane rural and suburban highways
  38. 38. Multilane Highways 38  Intended for analysis of uninterrupted-flow highway segments  Signal spacing > 2.0 miles  No on-street parking  No significant bus stops  No significant pedestrian activities
  39. 39. 39 Source: HCM, 2000
  40. 40. 40 Source: HCM, 2000 Step 1: Gather data Step 2: Calculate capacity (Supply)
  41. 41. 41 Source: HCM, 2000
  42. 42. 42 Source: HCM, 2000
  43. 43. Lane Width 43  Base Conditions: 12 foot lanes Source: HCM, 2000
  44. 44. Lane Width (Example) 44 Source: HCM, 2000 How much does use of 10-foot lanes decrease free flow speed? Flw = 6.6 mph
  45. 45. Lateral Clearance 45  Distance to fixed objects  Assumes  >= 6 feet from right edge of travel lanes to obstruction  >= 6 feet from left edge of travel lane to object in median Source: HCM, 2000
  46. 46. Lateral Clearance 46 TLC = LCR + LCL TLC = total lateral clearance in feet LCR = lateral clearance from right edge of travel lane LCL= lateral clearance from left edge of travel lane Source: HCM, 2000
  47. 47. 47 Source: HCM, 2000
  48. 48. 48 Example: Calculate lateral clearance adjustment for a 4-lane divided highway with milepost markers located 4 feet to the right of the travel lane. TLC = LCR + LCL = 6 + 4 = 10 Flc = 0.4 mph Source: HCM, 2000
  49. 49. 49 fm: Accounts for friction between opposing directions of traffic in adjacent lanes for undivided No adjustment for divided, fm = 1 Source: HCM, 2000
  50. 50. 50 Fa accounts for interruption due to access points along the facility Example: if there are 20 access points per mile, what is the reduction in free flow speed? Fa = 5.0 mph
  51. 51. Estimate Free flow Speed 51 BFFS = free flow under ideal conditions FFS = free flow adjusted for actual conditions From previous examples: FFS = 60 mph – 6.6 mph - 0.4 mph – 0 – 5.0 mph = 48 mph ( reduction of 12 mph)
  52. 52. 52 Source: HCM, 2000 Step 3: Estimate demand
  53. 53. 53 Calculate Flow Rate
  54. 54. Heavy Vehicle Adjustment 54  Heavy vehicles affect traffic  Slower, larger  fhv increases number of passenger vehicles to account for presence of heavy trucks
  55. 55. f(hv) General Grade Definitions: 55  Level: combination of alignment (horizontal and vertical) that allows heavy vehicles to maintain same speed as pass. cars (includes short grades 2% or less)  Rolling: combination that causes heavy vehicles to reduce speed substantially below P.C. (but not crawl speed for any length)  Mountainous: Heavy vehicles at crawl speed for significant length or frequent intervals  Use specific grade approach if grade less than 3% is more than ½ mile or grade more than 3% is more than ¼ mile)
  56. 56. 56 Example: for 10% heavy trucks on rolling terrain, what is Fhv? For rolling terrain, ET = 2.5 Fhv = _________1_______ = 0.87 1 + 0.1 (2.5 – 1)
  57. 57. Driver Population Factor (fp) 57  Non-familiar users affect capacity  fp = 1, familiar users  1 > fp >=0.85, unfamiliar users
  58. 58. 58 Source: HCM, 2000 Step 4: Determine LOS Demand Vs. Supply
  59. 59. 59  Calculate vp  Example: base volume is 2,500 veh/hour  PHF = 0.9, N = 2  fhv from previous, fhv = 0.87  Non-familiar users, fp = 0.85 vp = _____2,500 vph _____ = 1878 pc/ph/pl 0.9 x 2 x 0.87 x 0.85
  60. 60. Calculate Density 60 Example: for previous D = _____1878 vph____ = 39.1 pc/mi/lane 48 mph
  61. 61. 61 LOS = E Also, D = 39.1 pc/mi/ln, LOS E
  62. 62. Design Decision 62  What can we change in a design to provide an acceptable LOS?  Lateral clearance (only 0.4 mph)  Lane width  Number of lanes
  63. 63. Lane Width (Example) 63 Source: HCM, 2000 How much does use of 10 foot lanes decrease free flow speed? Flw = 6.6 mph
  64. 64. Recalculate Density 64 Example: for previous (but with wider lanes) D = _____1878 vph____ = 34.1 pc/mi/lane 55 mph
  65. 65. 65 LOS = E Now D = 34.1 pc/mi/ln, on border of LOS E
  66. 66. 66  Recalculate vp, while adding a lane  Example: base volume is 2,500 veh/hour  PHF = 0.9, N = 3  fhv from previous, fhv = 0.87  Non-familiar users, fp = 0.85 vp = _____2,500 vph _____ = 1252 pc/ph/pl 0.9 x 3 x 0.87 x 0.85
  67. 67. Calculate Density 67 Example: for previous D = _____1252 vph____ = 26.1 pc/mi/lane 48 mph
  68. 68. 68 LOS = D Now D = 26.1 pc/mi/ln, LOS D (almost C)

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