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TRAFFIC ANALYSIS TRANSPORTATION PLANNING TRAFFIC SAFETY

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Title: TRAFFIC ANALYSIS TRANSPORTATION PLANNING TRAFFIC SAFETY


1
TRAFFIC ANALYSIS TRANSPORTATION
PLANNINGTRAFFIC SAFETY
  • Developed for the
  • ASCE YMF PE REVIEW COURSE
  • August 27, 2007

2
COURSE REFERENCE SOURCES
  • Traffic and Highway Engineering,
  • Garber and Hoel, 1997.
  • PTOE Certification Program Refresher Course.
    Institute of Transportation Engineers. 2001.
  • Traffic Engineering,
  • Roess, McShane, and Prassas, 1997.
  • Highway Capacity Manual,
  • Transportation Research Board, 2000.
  • Six-Minute Solutions for Civil PE Exam
    Transportation Problems
  • Voigt, 2004.

3
COURSE OVERVIEW
  • What to bring to the test
  • Civil Engineering Reference Manual for the PE
    Exam, Lindeburg
  • Highway Capacity Manual, Transportation Research
    Board HCM
  • A Policy on Geometric Design of Highways and
    Streets, AASHTO The Green Book
  • Manual on Uniform Traffic Control Devices,
    Federal Highway Administration MUTCD

4
COURSE OVERVIEW
  • Course Goals
  • Answers lt 6 mins.
  • Review of concepts and procedures
  • Slides with notes will be included on ASCE YMF
    Course webpage

5
COURSE OVERVIEW
  • Morning Session 20 Transportation Topics
  • Transportation Planning
  • Traffic Safety
  • Pavement Design (Rigid and Flexible)
  • Surveying
  • Curves (Horizontal, Compound, Vertical)
  • Construction Staking

6
COURSE OVERVIEW
  • Transportation Afternoon Session
  • 13 Transportation Planning
  • Capacity Analysis
  • Origin Destination Studies
  • Site Impact Analysis
  • Trip Generation/Distribution Assignment
  • 13 Traffic Safety
  • High-Hazard Locations
  • Countermeasure Choices
  • Roadside Designs
  • Taper Design

7
COURSE OVERVIEW
  • Topics Covered Tonight
  • Traffic Flow Principles
  • Capacity Analysis
  • Multilane highways
  • Freeways
  • Signalized Intersections
  • Traffic Volume Studies
  • Speed Studies

8
COURSE OVERVIEW
  • Topics Covered Tonight (Continued)
  • Parking Operations Analysis
  • Sight Distance Analysis
  • Braking Distance Analysis
  • Pedestrian Facilities

9
COURSE OVERVIEW
  • Traffic analyses not covered tonight
  • Unsignalized Intersections (HCM Ch 17)
  • Mass Transit Studies (HCM Ch 14 and 27)
  • Traffic Control Devices
  • Bicycle Facilities (HCM Ch 11)
  • Driver Behavior and Performance
  • Freeway Weaving and Ramps (HCM Ch 24-26)

10
ASCE YMF PE REVIEW COURSE
  • Traffic Analysis
  • (Based on HCM Chapters 2 and 7)

11
Traffic Flow Principles
  • Uninterrupted Flow
  • Vehicles are not interrupted by external factors.
  • Interrupted Flow
  • Vehicle flow on interrupted flow facilities is
    influenced by external factors such as traffic
    signals, stop or yield signs, or frequent
    uncontrolled intersections or high volume
    driveways.

12
Traffic Flow Principles
  • Traffic Stream Parameters
  • Flow Rate or Volume
  • Speed
  • Density

13
Traffic Flow PrinciplesBasic Stream Parameters
14
Traffic Flow PrinciplesBasic Stream Parameters
  • Volume (veh per hour)
  • of vehicles that
  • pass a point on a roadway,
  • travel within a lane,
  • or travel in a given direction on a roadway
  • Flow Rate (veh per hour)
  • Based on time periods of lt1 hr
  • Converted to 1 hr time period

15
Traffic Flow Principles Peak Hour Factor (PHF)
  • Ties Hourly Volumes to Flow Rates
  • (typically 0.92)
  • For 15 minute periods

16
Traffic Flow Principles
  • Example
  • Find the peak hour
  • Find the peak hour factor (PHF)

Time Volume
700-715 500
715-730 550
730-745 650
745-800 675
800-815 625
815-830 575
17
Traffic Flow Principles
  • Example
  • Peak Hour
  • 700-800 500550650675 2,375
  • 715-815 550650675625 2,500
  • 730-830 650675625575 2,525
  • PHF
  • PHF Peak Hour / (4 x peak 15 minute vol)
  • PHF 2,525 / (4x675) 0.935

18
Traffic Flow Principles SpeedDistance Traveled
per Unit of Time
  • Time Mean Speed (TMS) Time mean speed is defined
    as the average speed of all vehicles passing a
    point over a specified time period.
  • Space Mean Speed (SMS) Space mean speed is
    defined as the average speed of all vehicles
    occupying a given section of roadway over a
    specific time period

19
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20
Traffic Flow Principles
  • Example
  • Assume a road section of 88 feet long (Note 60
    mph 88 fps). Four cars are timed through the
    section. Their times were 1 s, 1 s, 2 s, and
    1.5s.
  • What is the TMS?
  • What is the SMS

21
Traffic Flow Principles
  • Example
  • TMS 88/188/188/288/1.5 or individual speeds
    of 60 mph, 60 mph, 30 mph, and 45 mph
  • TMS (60603045)/4 48.7 mph

22
Traffic Flow Principles
  • Example
  • SMS add up the travel times and divide by the
    number of vehicles. Then divide the length of
    the section by average time
  • SMS 88 / ((1121.5)/4) 43.5 mph
  • Note SMS is always less than or equal to TMS

23
Traffic Flow Principles Travel Time
  • The time required to travel a segment of a given
    length.
  • Frequently used by traffic engineers to assess
    the performance of the transportation system

24
Traffic Flow Principles Density
  • Density is the number of vehicles in a given
    length of roadway or a lane. It is usually
    expressed in vehicles/km (vehicles/mile).

25
Traffic Flow Principles Uninterrupted Flow
Basic Relationship
  • q us k
  • q flow (veh/hour)
  • us space mean speed (km/h mph)
  • k density (veh/km veh/mile)

26
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27
Traffic Flow Principles Uninterrupted Flow - Key
Points
  • qm maximum flow or capacity
  • uf free flow speed when flows
    approach zero
  • uo optimum speed under maximum flow
    conditions
  • kj jam density when both flow and
    speed approach zero, and
  • ko optimum density under maximum
    flow conditions

28
Traffic Flow Principles Headway and Spacing
  • Microscopic Measures of Flow (individual
    vehicles)
  • Headway is the time between successive vehicles
    past a point.
  • Spacing is the distance between successive
    vehicles past a point

29
Traffic Flow Principles More Flow-Density
Relationships
  • Space Mean Speed Flow x Spacing
  • Density Flow x Travel Time
  • Spacing Space mean speed x Headway
  • Headway Travel Time x Spacing

30
Traffic Flow Principles Interrupted Flow
  • Saturation Flow Rate
  • (usually 1900 pcphpl _at_ intersections)
  • s 3600
  • h
  • s saturation flow rate (veh/hr/lane)
  • h average headway (sec)

31
Traffic Flow Principles Delay
  • Signalized Intersections
  • Control Delay
  • Stop Controlled Intersections
  • Control Delay

32
CAPACITY ANALYSES
  • Highway Capacity Manual (HCM) governs
  • Urban Streets (Chapters 10 and 15)
  • Two-Lane Highways (Chapters 12 and 20)
  • Multilane Highways (Chapters 12 and 21)
  • Freeways (Chapters 13, 22, and 23)
  • Signalized Intersections (Chapter 16)
  • Unsignalized Intersections (Chapter 17)

33
CAPACITY ANALYSES Level Of Service Definitions
HCM Chapter Facility Unit
15 Urban Street Average Travel Speed (mph)
20 Two-Lane Highway Average Travel Speed (mph) Time Spent Following
21 Multilane Highway Density (pc/mi/ln)
22, 23 Freeway Density (pc/mi/ln)
16 Signalized Intersections Control Delay per vehicle (sec/veh)
17 Unsignalized Intersections (not covered tonight) Control Delay per vehicle (sec/veh)
34
CAPACITY ANALYSES Urban Street Methodology
  • HCM page 15-2
  • Define Segments and Sections
  • Determine Free-Flow Speed
  • Compute Running Time and Intersection Delays (or
    record delay and travel time)
  • Compute Average Travel Speed
  • Determine LOS

35
CAPACITY ANALYSES Two-Lane Highway Methodology
  • HCM page 20-2
  • Define Average Travel Speed
  • Compute Free-Flow Speed
  • Adjust Demand Volume for Average Speed and
    Time-Spent Following
  • Compute Flow Rates, Average Travel Speed,
    Time-Spent-Following
  • Determine LOS

36
CAPACITY ANALYSES Multilane Highway Methodology
  • For Partial or no access control with a Divided
    Cross-Section
  • Full Access Control and Undivided Cross-Section
  • 4 or more through lanes and two-way operation
  • 2-3 through lanes and one-way operation

37
CAPACITY ANALYSES Multilane Highway Methodology
  • HCM page 21-2
  • Calculate Free Flow Speed (FFS) and Flow Rate
  • Define Speed-Flow Curve
  • Determine Speed from Speed-Flow Curve
  • Compute density as f(flow rate, speed)
  • Determine LOS

38
CAPACITY ANALYSES Freeways
  • Divided Highway
  • Access Control
  • Uninterrupted flow

39
CAPACITY ANALYSES Freeway Capacity
  • Levels of Service - A to F
  • A - Best operating conditions
  • F - Worst operating conditions
  • Segments
  • Basic Freeway Sections
  • Weaving Areas
  • Ramp Junctions

40
CAPACITY ANALYSES Flow Rates Under Ideal
Conditions
  • 3.6 m (12 ft) traffic lanes and no obstructions
    within 1.87 m (6 ft) of the pavement edge.
  • Level terrain with geometric conditions that
    would allow free flow speeds of 70 mph (110
    km/h).
  • Only passenger cars in the traffic stream.

41
CAPACITY ANALYSES Freeway Segment Methodology
  • HCM page 23-2
  • Calculate Free Flow Speed (FFS) or Flow Rate
  • Define Speed-Flow Curve
  • Determine Speed
  • Compute Density
  • Determine LOS

42
CAPACITY ANALYSES Basic Freeway Section Capacity
Calculation Procedures
  • Flow Rates
  • Free Flow Speed
  • Density
  • Level of Service

43
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44
CAPACITY ANALYSES Free Flow Speed
  • By field measurement of speeds on a freeway
    section determined by a spot speed study.
  • By estimating free flow speeds on the basis of
    physical characteristics.

45
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46
CAPACITY ANALYSES Level of Service
47
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48
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49
CAPACITY ANALYSES TRAFFIC SIGNAL OPERATION
  • Pretimed Control
  • Consistent Cycle and Interval Lengths
  • Lower Installation and Maintenance Costs
  • Simpler Operation
  • Traffic Actuated Control
  • Responds to Changing Traffic Flows
  • Greater Efficiency
  • Minimizes Delay
  • Minimizes Some Crashes

50
CAPACITY ANALYSES PRINCIPLES OF SIGNAL PHASING
  • Number of Phases Depends on Geometric Design,
    Volume, and Pedestrians
  • Phase to Minimize Potential Hazards
  • As Number of Phases Increases, Total Delay
    Increases
  • Use the Minimum Number of Phases to Accommodate
    Traffic

51
CAPACITY ANALYSES PRINCIPLES OF SIGNAL TIMING
  • Relatively Short Cycles Reduce Delay
  • Green Intervals Should Be Proportional to Traffic
    Demand
  • Timing Must Accommodate Pedestrians
  • Phase Change Intervals Must Ensure that Vehicles
    can either Stop or Clear the Intersection
  • Must Be Field-Checked

52
CAPACITY ANALYSES Cycle Length
  • Optimal Cycle (Co)
  • Co 1.5L 5
  • 1 SYi
  • L Lost time per cycle, sec (3.5s Yel 1s Red)
  • Yi Vi / Si
  • (Flow Rate / Saturation Flow Rate)

53
CAPACITY ANALYSES Phase Change Interval
  • CP Yellow Red

54
CAPACITY ANALYSES
  • Example
  • Four leg intersection with approach speeds of 35
    mph. Width of all approaches is 48 feet.
    Average length of vehicle is 20 feet.
    Deceleration is 10 ft/sec2. Perception reaction
    time is 2.5 sec. What is minimum clearance
    interval?

55
CAPACITY ANALYSES
  • Example
  • Convert mph to ft/sec 35 mph 51.3 ft/sec
  • CP 2.5 sec 51.3 ft/sec (48 ft 20
    ft)
  • (2(10ft/sec2) 0) 51.3
    ft/sec
  • CP 6.4 sec

56
CAPACITY ANALYSES COORDINATED SIGNALS
  • Reduced Travel Time and Delay
  • Reduced Stops, Fuel Consumption, Air Pollutant
    Emissions, and Vehicle Costs
  • Reduction of Stopping Crashes
  • Built-In Speed Control

57
CAPACITY ANALYSES COORDINATED SIGNALS
FACTORS TO CONSIDER
  • Signal Spacing
  • Directional Movement
  • Signal Phasing
  • Arrival Patterns
  • Traffic Fluctuation
  • Incompatible Signal Cycle Requirements

58
CAPACITY ANALYSES COORDINATED SIGNALSSystem
Cycle Length
  • Set at even multiple of average travel time
    between signals

59
CAPACITY ANALYSES Capacity of Signalized
Intersections5 Modules
  • Input
  • Volume Adjustment
  • Saturation Flow Rate
  • Capacity Analysis
  • Level of Service

60
CAPACITY ANALYSES Capacity of Signalized
IntersectionsInput Module
  • Geometric Conditions
  • Traffic Conditions
  • Signalization Conditions

61
CAPACITY ANALYSES Capacity of Signalized
IntersectionsVolume Adjustment Module
  • Peak Hour Factor
  • Establish Lane Groups
  • Assign Volumes to Lane Groups

62
CAPACITY ANALYSES Capacity of Signalized
IntersectionsSaturation Flow Rate Module
  • Ideal Saturation Flow Rate
  • Adjustments

63
CAPACITY ANALYSES Capacity of Signalized
IntersectionsSaturation Flow Rate
s sONfwfhvfgfpfbbfaflufrtflt
64
CAPACITY ANALYSES Capacity of Signalized
IntersectionsCapacity Analysis Module
  • Compute Lane Group Capacities
  • Compute Lane Group v/c Ratios
  • Aggregate Results

65
CAPACITY ANALYSES Capacity of Signalized
IntersectionsLevel of Service Module
  • Compute Lane Group Delays
  • Aggregate Delays
  • Determine Levels of Service

66
CAPACITY ANALYSES Capacity of Signalized
IntersectionsControl Delay
  • Where d1 uniform control delay
  • PF progression adjustment factor
  • d2 incremental delay
  • d3 residual demand delay

67
INTERMISSION
68
OTHER ANALYSES
  • Traffic Volume Analyses
  • Speed Studies
  • Parking Operations
  • Gap Acceptance / Queuing Analyses
  • Sight Distance / Braking Analysis / Skidmark
    Analysis
  • Pedestrian Analysis

69
TRAFFIC VOLUME ANALYSISTraffic Volume Studies
  • Typical purposes of volume studies
  • Annual average daily traffic (AADT)
  • Average daily traffic (ADT) snapshot
  • Hourly traffic
  • Short-term counts

70
TRAFFIC VOLUME ANALYSIS Types of Volume Studies
  • Street counts directional counts
  • Turning movement counts
  • Classification counts
  • Occupancy counts
  • Pedestrian counts

71
TRAFFIC VOLUME ANALYSIS Typical Counting Periods
  • 24-hour
  • 16-hour - about 90 of the ADT
  • 12-hour - often 7 am to 7 pm
  • Peak periods
  • Typically 7-9 am, 4-6 pm
  • Modified for larger urban areas
  • Weekend counts
  • Adjust counts for daily and seasonal variations

72
TRAFFIC VOLUME ANALYSIS Spot Speed Studies
  • Typical purposes of speed studies
  • Speed trends over time
  • Traffic control planning
  • Before-and-after studies
  • Accident analyses
  • Geometric design
  • Research studies

73
TRAFFIC VOLUME ANALYSIS Study Locations
  • Consistent with study purpose
  • Not where vehicles are accelerating
  • Data collectors must not influence vehicle speeds
  • Factors that influence speeds
  • Physical conditions
  • Environment
  • Traffic

74
TRAFFIC VOLUME ANALYSIS Selecting the Sample
  • Random but representative
  • At least 100 vehicles
  • Freeflowing vehicles only
  • Common sampling errors
  • Always selecting platoon leader
  • Too many trucks
  • High proportion of speeders
  • Other events

75
TRAFFIC VOLUME ANALYSIS Data Collection Methods
  • Time versus measured distance
  • Distance versus measured time
  • Radar meter
  • Doppler principle
  • Radar detectors
  • Laser speed meter

76
TRAFFIC VOLUME ANALYSIS Cosine Correction
77
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78
TRAFFIC VOLUME ANALYSIS Typical Speed Parameters
  • Calculations
  • Mean and median
  • Standard deviation
  • Standard error
  • Confidence interval
  • Graphical
  • 85th percentile
  • 10-mph pace

79
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80
PARKING STUDIES
  • Merchants or residents complain that parking
    demand exceeds parking supply
  • Undertake space inventory
  • Assign numbers or addresses
  • Include illegal spaces
  • Prepare sketch or table
  • Design usage study
  • Determine circulation interval
  • Disaggregate by block face

81
Parking Study Zones
82
TRAFFIC VOLUME ANALYSIS Sample License Plate
Survey Form
83
TRAFFIC VOLUME ANALYSIS Parking Turnover
  • Number of Parked Veh .
  • Number of Parking Spaces

84
TRAFFIC VOLUME ANALYSIS Parking Duration
  • Number of Observations x Interval
  • Number of Vehicles

85
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86
GAP ACCEPTANCE

Average number of vehicles arriving per unit time
period ? V T ? average number of
vehicles arriving per unit time period V volume
of vehicles arriving during time period T T
time period (usually seconds)
87
GAP ACCEPTANCE

Probability of a Gap P (hgtt) e-?t P (hltt) 1
- e-?t P (hgtt) probability of a gap
greater than t seconds P (hltt) probability of a
gap less than t seconds
88
QUEUING ANALYSIS
  • For random vehicle arrivals with
  • Poisson statistical distribution
  • Em ?2 / µ(µ-?) avg length
  • Ew ? / µ(µ-?) avg wait time
  • P (ngtN) (? / µ) N1 Probability
  • of more than N vehicles in the queue
  • ? Arrival Flow Rate (veh/min)
  • µ Departure Flow Rate (veh/min)

89
DISTANCES FOR ANALYSIS
  • Braking Distance (Speed Reduction)
  • Db u12-u22
  • 30 (f G)
  • Passing Sight Distance (PSD)
  • Decision Sight Distance (DSD)

90
DISTANCES FOR ANALYSIS
  • Stopping Sight Distance
  • Two components distance traveled during
    perception/reaction and braking distance.
  • Assumes wet pavement and tires, poor tire
    conditions, emergency braking.

91
DISTANCES FOR ANALYSIS Design Criteria
  • Perception/Reaction Time
  • Time required for driver to see and identify a
    stimulus and react.
  • AASHTO recommends 2.5 seconds for design.
  • Commonly used in determining stopping sight
    distance.

92
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93
DISTANCES FOR ANALYSIS Design Criteria
  • Driver Eye Height
  • 1070 mm (3.5 feet) for SSD.
  • Object Height
  • 150 mm (6 inches) for SSD.
  • 1300 mm (4.25 feet) for PSD.

94
DISTANCES FOR ANALYSIS Driver Eye and Object
Height
H1 driver eye height H2 object height S
stopping sight distance
95
DISTANCES FOR ANALYSIS Skid Mark Velocity
Estimates
  • uu db uk2 u12 1/2
  • dk
  • uu unknown velocity
  • db braking distance (average of four skid
    marks)
  • dk distance traveled during trial run
  • uk speed of trial run by traffic engines
  • u1 speed at impact

96
SHOCKWAVE THEORY
Describes shifting bottleneck condition along a
highway uw q2 q1 k2 k1 uw speed
of shock wave q2 flow downstream of
bottleneck q1 flow upstream of bottleneck k2
density downstream of bottleneck k1 density
upstream of bottleneck
97
ASCE YMF PE REVIEW COURSE
  • Transportation Planning

98
SITE IMPACT ANALYSISPurpose
  • To determine the needs for any improvements to
    the adjacent and nearby road system to maintain a
    satisfactory level of service, safety, and access
    to a proposed development.

99
SITE IMPACT ANALYSIS When is a Study Needed?
  • When the development will generate a specific
    number of peak hour trips
  • When the development will generate a specific
    number of daily trips
  • When development size exceeds a specified limit
  • At the government agencys discretion
  • When development occurs in a sensitive area
  • When financial assessments are required
  • Clark County gt300 peak hour trips

100
SITE IMPACT ANALYSIS Study Area Limits
  • All site access drives
  • Adjacent roadways and major intersections
  • First signalized intersection in each direction
    from the site based on local policy
  • Additional areas as specified by local policy

101
SITE IMPACT ANALYSIS Study Horizon
  • Anticipated opening day of major phases
  • Anticipated date of full build-out
  • Five years after full build-out

102
SITE IMPACT ANALYSIS Steps in the Process
  • Site Traffic Generation
  • Site Traffic Assignment and Distribution
  • Non-site Traffic Forecast
  • Analysis of level of service at signalized and
    non-signalized locations
  • Site Access Improvements
  • Internal Site Circulation and Parking Analysis

103
SITE IMPACT ANALYSIS Site Traffic GenerationITE
Trip Generation
  • Select Rates or Equations
  • Identify Time Periods
  • Identify Day or Season
  • Correct for Mixed Use Developments

104
SITE IMPACT ANALYSIS Site Traffic Distribution
Methods
  • Analogy Similar models
  • Trip Distribution Model
  • Surrogate Data - Local Knowledge

105
SITE IMPACT ANALYSIS Assignment to Drives
106
SITE IMPACT ANALYSIS Pass-By Traffic
  • Traffic already on adjacent roadways that will be
    diverted to the new development

107
SITE IMPACT ANALYSIS Total Area Wide Assignment
  • Site Traffic
  • Non-site (Background)Traffic - Consider Design
    Year

108
SITE IMPACT ANALYSIS Site Access Improvements
  • Laneage
  • Turning lanes
  • Turning lane storage requirements
  • Curb return radii at intersections
  • Signal timing individual intersections and
    systems
  • Acceleration and deceleration lanes
  • Access control at right-in and right-out only
    access points

109
SITE IMPACT ANALYSIS Internal Site Circulation
and Parking Requirements
  • Location of access points with respect to traffic
    generators within the site.
  • The internal roadway circulation pattern
  • Provisions for service and delivery vehicles
  • Available storage space (queuing space) at exits
    from the site

110
SITE IMPACT ANALYSIS Internal Site Circulation
and Parking Requirements (cont)
  • Parking facilities layout and number of spaces,
    relation to the internal
  • roadway, network, etc.
  • Pedestrian, transit, bicycle, and handicapped
    facilities
  • Traffic control devices signs and markings

111
SITE IMPACT ANALYSIS
  • Example
  • New development has 300 condos and 150 single
    family homes. What is the trip generation? How
    many exiting PM trips are there?

Land Use PM Peak Hour PM Peak Hour PM Peak Hour
Land Use Rate (trips/DU) In Out
Condo 1 75 25
Single Family Home 0.9 65 35
112
SITE IMPACT ANALYSIS
  • Example
  • Trip Generation 300(1) 150(0.9) 435
  • PM Exiting Trips 300(1)(0.25) 150(0.9)(0.35)
    122

113
ASCE YMF PE REVIEW COURSE
  • Traffic Safety

114
TRAFFIC SAFETYROADWAY AND ROADSIDE SAFETY
CONCEPTS
  • Safety not an Automatic By-Product
  • Highway Features Affect Safety By
  • Driver Ability to Maintain Control and Recognize
    Hazards
  • Frequency and Severity of Conflicts
  • Consequences of Leaving Traveled Way
  • Attentiveness of Driver

115
TRAFFIC SAFETYAN IDEAL HIGHWAY
  • Uniformly High-Quality Design
  • Avoid Discontinuities

116
TRAFFIC SAFETYDESIGN INFLUENCE ON SAFETY
  • Alignment and Cross Section Design
  • Sight Distance
  • Intersection Safety
  • Left Turns
  • Sight Distance
  • Access Control
  • Pedestrians
  • Roadsides
  • Traffic Signing and Pavement Marking
  • Traffic Signals

117
TRAFFIC SAFETYTraffic Safety Analyses
  • Identification of High-Hazard Locations
  • Countermeasure Choices
  • Intersection Conflicts and Control
  • Roadside Designs
  • Color Codes
  • Taper Design

118
TRAFFIC SAFETYIDENTIFICATION OF HIGH-HAZARD
LOCATIONS
  • Crash Frequency
  • Crash Rate
  • Number-Rate
  • Equivalent Property Damage Only Rate
  • Rate Quality Control
  • Other Indicators

119
TRAFFIC SAFETYCRASH FREQUENCY
  • Bias Towards Higher Volume Traffic Sections
  • Can Categorize Roadway Segments According to
    Functional Classification

120
TRAFFIC SAFETYCRASH RATE
SEGMENT CRASH RATE
  • Rseg A x 105
  • (365 x T x V x L)

SPOT CRASH RATE
Rspot A x 105 (365 x T x V)
121
TRAFFIC SAFETYNUMBER-RATE
  • First Rank By Crash Frequency
  • Remove Locations Below Threshold Frequency
  • Re-Rank by Crash Rate

122
TRAFFIC SAFETYEQUIVALENT PROPERTY DAMAGE ONLY
(EPDO) RATE
  • Give Greater Weight to More Severe Crashes
  • Convert Injury and Fatal Crashes to Equivalent
    Property Damage Only Crashes
  • Establishing Unbiased Weighting Factors is
    Difficult

123
TRAFFIC SAFETYRATE QUALITY CONTROL
Rc Critical Crash Rate Ra Average Crash Rate
for Similar Locations K Level of Confidence
Factor V Volume of Traffic K Level of
Confidence 1.282 90 1.645 95 2.327 99
124
TRAFFIC SAFETYOTHER NON-CRASH INDICATORS
  • Pavement Skid Testing
  • Evidence of Evasive Actions
  • Capacity Deficiencies
  • Number of Access Points
  • Traffic Conflicts Analysis

125
TRAFFIC SAFETYANALYSIS OF HIGH-HAZARD LOCATIONS
PATTERNS
  • Left-Turn/Head On
  • Right Angle
  • Rear-End
  • Sideswipe
  • Pedestrian
  • Bicycle
  • Run-Off-The Road
  • Fixed Object
  • Head-On
  • Parked Vehicle
  • Animal
  • Others

126
TRAFFIC SAFETYCOLLISION DIAGRAM
  • Direction of Travel and Intended Maneuvers
  • Non-Contact Vehicles Involved
  • Date, Day of Week and Time of Day
  • Unusual Conditions

127
COLLISION DIAGRAM
128
TRAFFIC SAFETYSELECTING COUNTERMEASURES
  • Countermeasure Should Provide Greatest Benefits
    Relative to Costs
  • Not All Problems Can Be Solved (3 Es)
  • Full Range of Alternatives Should Be Considered
  • Evaluate Effectiveness of Improvements

129
TRAFFIC SAFETYPRIORITIZATION OF IMPROVEMENTS
  • Based On
  • Funding
  • Project Costs
  • Crash Reduction Benefits

130
TRAFFIC SAFETYIMPROVEMENT PROJECT PLANNING
  • Select Package of Improvement Projects to Make
    Optimum Use of Resources
  • Also Consider
  • Social/Environmental Impacts
  • Budget Constraints
  • Geographic Distribution of Improvements

131
TRAFFIC SAFETYIMPLEMENTATION OF PROJECTS
  • Implement as Quickly as Practicable

132
TRAFFIC SAFETYEVALUATION OF IMPLEMENTED PROJECTS
  • Provides Information to Improve Future
    Decision-Making
  • Learn From Success (or Failure) of Implemented
    Projects

133
TRAFFIC SAFETYIntersections
134
TRAFFIC SAFETY
  • Example
  • How many conflict points are there for a two-way,
    unsignalized, T intersection?

135
TRAFFIC SAFETY
  • Example

136
TRAFFIC SAFETYHierarchy of Intersection Control
  • Uncontrolled where basic rules of the road apply
  • Stop or Yield control where stop control can be
    either two-way or multi-way control
  • Signal control

137
TRAFFIC SAFETYWarrantsAASHTO MUTCD
  • Uncontrolled Intersections
  • Sight Distance
  • Yield or 2-way Stop
  • Priority
  • Multi-way Stop
  • Volumes
  • Crashes

138
TRAFFIC SAFETYTRAFFIC CONTROL SIGNALS
When Properly Designed and Located
  • Provide Orderly Flow of Traffic
  • Reduce Frequency of Some Crashes
  • Increase Capacity
  • Provides Gap for Minor Movements

139
TRAFFIC SAFETYTRAFFIC CONTROL SIGNALS
When Improperly Designed or Located
  • Increase Delay and Fuel Consumption
  • Increase Certain Types of Crashes
  • Increase Frustration
  • Induce Road Users to Use Less Appropriate Routes

140
TRAFFIC SAFETYMUTCD SIGNAL WARRANTS
  • Warrant 1, Eight-Hour Vehicular Volume
  • Warrant 2, Four-Hour Vehicular Volume
  • Warrant 3, Peak Hour Volume
  • Warrant 4, Pedestrian Volume
  • Warrant 5, School Crossing
  • Warrant 6, Coordinated Signal System
  • Warrant 7, Crash Experience
  • Warrant 8, Roadway Network

141
TRAFFIC SAFETYRoadside Cross Section Elements
  • Horizontal Clearance to Obstructions
  • Clear zone concept
  • Run-off road accidents.
  • 9 meters for high functional class roads.
  • 3 meters for low-speed, rural roads.
  • Remove, relocate, redesign, or shield objects.
  • Medians
  • Storage space for left-turning and U-turning
    vehicles.
  • Two-way left-turn lanes improve capacity at
    intersections.

142
Clear Zone Widths
Source Roadside Design Guide (1996)
143
TRAFFIC SAFETYSignage / Striping Colors
  • Blackregulation
  • Blueroad user services guidance, tourist
    information, and evacuation route
  • Brownrecreational and cultural interest area
    guidance
  • Coralunassigned
  • Fluorescent Pinkincident management

144
TRAFFIC SAFETYSignage / Striping Colors
  • Fluorescent Yellow-Greenpedestrian warning,
    bicycle warning, playground warning, school bus
    and school warning
  • Greenindicated movements permitted, direction
    guidance
  • Light Blueunassigned
  • Orangetemporary traffic control
  • Purpleunassigned
  • Redstop or prohibition
  • Whiteregulation
  • Yellowwarning

145
Taper Length
146
Taper Length
147
TRAFFIC SAFETYPedestrian Level of Service
  • HCM Chapter 18
  • Walkways and Sidewalks
  • Separated from vehicular traffic
  • Separated from bicycle facilities
  • Primary Measurement is Space the inverse of
    Density

148
TRAFFIC SAFETYPedestrian Level of Service
  • vp v15 / (15 WE)
  • vp pedestrian unit flow rate (p/min/ft)
  • v15 peak 15-min flow rate (p/15-min)
  • WE effective walkway width
  • HCM Exhibit 18-3 shows Average Flow LOS Criteria
    for Walkways
  • LOS C 7 p/min/ft lt Flow Rate lt 10 p/min/ft

149
TRAFFIC SAFETYPedestrian Level of Service
  • What is WE?
  • The portion of the walkway that can be used
    effectively by pedestrians
  • WE WT - WO
  • WE effective walkway width (ft)
  • WT total walkway width (ft)
  • WO sum of widths and shy distances (ft)
  • See HCM Exhibit 18-1 and 18-2

150
TRAFFIC SAFETYPedestrian Level of Service
151
CONTACT INFORMATION
  • Molly OBrien, P.E.
  • Kimley-Horn and Associates, Inc.
  • 702.862.3636
  • Molly.obrien_at_kimley-horn.com
  • Special Thanks to
  • Paul Vilaluz, P.E., PTOE
  • Martin and Martin
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