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TRAFFIC ANALYSIS TRANSPORTATION PLANNING TRAFFIC SAFETY. Developed for the ASCE YMF PE REVIEW COURSE August 27, 2007. COURSE REFERENCE SOURCES. Traffic and Highway Engineering , Garber and Hoel, 1997.

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traffic analysis transportation planning traffic safety

TRAFFIC ANALYSISTRANSPORTATION PLANNINGTRAFFIC SAFETY

Developed for the

ASCE YMF PE REVIEW COURSE

August 27, 2007

course reference sources

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.

course overview
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”
course overview4
COURSE OVERVIEW
  • Course Goals
    • Answers < 6 mins.
    • Review of concepts and procedures
    • Slides with notes will be included on ASCE YMF Course webpage
course overview5
COURSE OVERVIEW
  • Morning Session – 20% Transportation Topics
    • Transportation Planning
    • Traffic Safety
    • Pavement Design (Rigid and Flexible)
    • Surveying
    • Curves (Horizontal, Compound, Vertical)
    • Construction Staking
course overview6
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
course overview7
COURSE OVERVIEW
  • Topics Covered Tonight
    • Traffic Flow Principles
    • Capacity Analysis
      • Multilane highways
      • Freeways
      • Signalized Intersections
    • Traffic Volume Studies
    • Speed Studies
course overview8
COURSE OVERVIEW
  • Topics Covered Tonight (Continued)
    • Parking Operations Analysis
    • Sight Distance Analysis
    • Braking Distance Analysis
    • Pedestrian Facilities
course overview9
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)
asce ymf pe review course

ASCE YMF PE REVIEW COURSE

Traffic Analysis

(Based on HCM Chapters 2 and 7)

traffic flow principles
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.
traffic flow principles12
Traffic Flow Principles
  • Traffic Stream Parameters
      • Flow Rate or Volume
      • Speed
      • Density
traffic flow principles basic stream parameters14

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 <1 hr

Converted to 1 hr time period

traffic flow principles peak hour factor phf

Traffic Flow PrinciplesPeak Hour Factor (PHF)

Ties Hourly Volumes to Flow Rates

(typically 0.92)

For 15 minute periods:

traffic flow principles16
Traffic Flow Principles

Example

Find the peak hour

Find the peak hour factor (PHF)

traffic flow principles17
Traffic Flow Principles

Example

  • Peak Hour
    • 7:00-8:00 = 500+550+650+675 = 2,375
    • 7:15-8:15 = 550+650+675+625 = 2,500
    • 7:30-8:30 = 650+675+625+575 = 2,525
  • PHF
    • PHF = Peak Hour / (4 x peak 15 minute vol)
    • PHF = 2,525 / (4x675) = 0.935
traffic flow principles speed distance traveled per unit of time
Traffic Flow PrinciplesSpeedDistance 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
traffic flow principles20
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

traffic flow principles21
Traffic Flow Principles
  • Example

TMS: 88/1+88/1+88/2+88/1.5 or individual speeds of 60 mph, 60 mph, 30 mph, and 45 mph

TMS = (60+60+30+45)/4 = 48.7 mph

traffic flow principles22
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 / ((1+1+2+1.5)/4) = 43.5 mph

Note: SMS is always less than or equal to TMS

traffic flow principles travel time

Traffic Flow PrinciplesTravel 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

traffic flow principles density

Traffic Flow PrinciplesDensity

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

traffic flow principles uninterrupted flow basic relationship

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])

traffic flow principles uninterrupted flow key points
Traffic Flow PrinciplesUninterrupted 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

traffic flow principles headway and spacing

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

traffic flow principles more flow density relationships

Traffic Flow Principles MoreFlow-Density Relationships

Space Mean Speed = Flow x Spacing

Density = Flow x Travel Time

Spacing = Space mean speed x Headway

Headway = Travel Time x Spacing

traffic flow principles interrupted flow

Traffic Flow PrinciplesInterrupted Flow

Saturation Flow Rate

(usually 1900 pcphpl @ intersections)

s = 3600

h

s = saturation flow rate (veh/hr/lane)

h = average headway (sec)

traffic flow principles delay

Traffic Flow PrinciplesDelay

Signalized Intersections:

Control Delay

Stop Controlled Intersections:

Control Delay

capacity analyses
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)
capacity analyses urban street methodology
CAPACITY ANALYSESUrban 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
capacity analyses two lane highway methodology
CAPACITY ANALYSESTwo-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
capacity analyses multilane highway methodology
CAPACITY ANALYSESMultilane 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
capacity analyses multilane highway methodology37
CAPACITY ANALYSESMultilane 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
capacity analyses freeways
CAPACITY ANALYSESFreeways
  • Divided Highway
  • Access Control
  • Uninterrupted flow
capacity analyses freeway capacity
CAPACITY ANALYSESFreeway Capacity
  • Levels of Service - A to F
    • A - Best operating conditions
    • F - Worst operating conditions
  • Segments
    • Basic Freeway Sections
    • Weaving Areas
    • Ramp Junctions
capacity analyses flow rates under ideal conditions
CAPACITY ANALYSESFlow 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.
capacity analyses freeway segment methodology
CAPACITY ANALYSESFreeway Segment Methodology

HCM page 23-2

  • Calculate Free Flow Speed (FFS) or Flow Rate
  • Define Speed-Flow Curve
  • Determine Speed
  • Compute Density
  • Determine LOS
capacity analyses basic freeway section capacity calculation procedures

CAPACITY ANALYSESBasic Freeway Section Capacity Calculation Procedures

Flow Rates

Free Flow Speed

Density

Level of Service

capacity analyses free flow speed
CAPACITY ANALYSESFree 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.
capacity analyses traffic signal operation
CAPACITY ANALYSESTRAFFIC 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
capacity analyses principles of signal phasing
CAPACITY ANALYSESPRINCIPLES 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
capacity analyses principles of signal timing
CAPACITY ANALYSESPRINCIPLES 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
capacity analyses cycle length
CAPACITY ANALYSESCycle Length
  • Optimal Cycle (Co)

Co = 1.5L + 5

1 – ΣYi

L = Lost time per cycle, sec (3.5s Yel + 1s Red)

Yi = Vi /Si

= (Flow Rate / Saturation Flow Rate)

capacity analyses54
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?

capacity analyses55
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

capacity analyses coordinated signals
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
capacity analyses coordinated signals57
CAPACITY ANALYSES COORDINATED SIGNALS

FACTORS TO CONSIDER

  • Signal Spacing
  • Directional Movement
  • Signal Phasing
  • Arrival Patterns
  • Traffic Fluctuation
  • Incompatible Signal Cycle Requirements
capacity analyses coordinated signals system cycle length

CAPACITY ANALYSESCOORDINATED SIGNALSSystem Cycle Length

Set at even multiple of average travel time between signals

capacity analyses capacity of signalized intersections 5 modules
CAPACITY ANALYSESCapacity of Signalized Intersections5 Modules:
  • Input
  • Volume Adjustment
  • Saturation Flow Rate
  • Capacity Analysis
  • Level of Service
capacity analyses capacity of signalized intersections input module
CAPACITY ANALYSESCapacity of Signalized IntersectionsInput Module:
  • Geometric Conditions
  • Traffic Conditions
  • Signalization Conditions
capacity analyses capacity of signalized intersections volume adjustment module
CAPACITY ANALYSESCapacity of Signalized IntersectionsVolume Adjustment Module:
  • Peak Hour Factor
  • Establish Lane Groups
  • Assign Volumes to Lane Groups
capacity analyses capacity of signalized intersections saturation flow rate module
CAPACITY ANALYSESCapacity of Signalized IntersectionsSaturation Flow Rate Module:
  • Ideal Saturation Flow Rate
  • Adjustments
capacity analyses capacity of signalized intersections saturation flow rate
CAPACITY ANALYSESCapacity of Signalized IntersectionsSaturation Flow Rate

s =sONfwfhvfgfpfbbfaflufrtflt

capacity analyses capacity of signalized intersections capacity analysis module
CAPACITY ANALYSESCapacity of Signalized IntersectionsCapacity Analysis Module:
  • Compute Lane Group Capacities
  • Compute Lane Group v/c Ratios
  • Aggregate Results
capacity analyses capacity of signalized intersections level of service module
CAPACITY ANALYSESCapacity of Signalized IntersectionsLevel of Service Module:
  • Compute Lane Group Delays
  • Aggregate Delays
  • Determine Levels of Service
capacity analyses capacity of signalized intersections control delay

CAPACITY ANALYSESCapacity of Signalized IntersectionsControl Delay:

Where d1 = uniform control delay

PF = progression adjustment factor

d2 = incremental delay

d3 = residual demand delay

other analyses
OTHER ANALYSES
  • Traffic Volume Analyses
  • Speed Studies
  • Parking Operations
  • Gap Acceptance / Queuing Analyses
  • Sight Distance / Braking Analysis / Skidmark Analysis
  • Pedestrian Analysis
traffic volume analysis traffic volume studies
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
traffic volume analysis types of volume studies
TRAFFIC VOLUME ANALYSIS Types of Volume Studies
  • Street counts; directional counts
  • Turning movement counts
  • Classification counts
  • Occupancy counts
  • Pedestrian counts
traffic volume analysis typical counting periods
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
traffic volume analysis spot speed studies
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
traffic volume analysis study locations
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
traffic volume analysis selecting the sample
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
traffic volume analysis data collection methods
TRAFFIC VOLUME ANALYSIS Data Collection Methods
  • Time versus measured distance
  • Distance versus measured time
  • Radar meter
    • Doppler principle
    • Radar detectors
  • Laser speed meter
traffic volume analysis typical speed parameters
TRAFFIC VOLUME ANALYSIS Typical Speed Parameters
  • Calculations
    • Mean and median
    • Standard deviation
    • Standard error
    • Confidence interval
  • Graphical
    • 85th percentile
    • 10-mph pace
parking studies
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
traffic volume analysis parking turnover

TRAFFIC VOLUME ANALYSIS Parking Turnover

Number of Parked Veh .

Number of Parking Spaces

traffic volume analysis parking duration

TRAFFIC VOLUME ANALYSIS Parking Duration

Number of Observations x Interval

Number of Vehicles

gap acceptance

GAP ACCEPTANCE

Average number of vehicles arriving per unit time period

  • λ = V

T

λ = average number of vehicles arriving per unit time period

V = volume of vehicles arriving during time period T

T = time period (usually seconds)

gap acceptance87

GAP ACCEPTANCE

Probability of a Gap

  • P (h>t) = e-λt
  • P (h<t) = 1 - e-λt

P (h>t) = probability of a gap greater than t seconds

P (h<t) = probability of a gap less than t seconds

queuing analysis

QUEUING ANALYSIS

For random vehicle arrivals with

Poisson statistical distribution

Em = λ2 / μ(μ-λ) = avg length

Ew = λ / μ(μ-λ) = avg wait time

P (n>N) = (λ / μ) N+1 = Probability

of more than N vehicles in the queue

λ = Arrival Flow Rate (veh/min)

μ = Departure Flow Rate (veh/min)

distances for analysis
DISTANCES FOR ANALYSIS
  • Braking Distance (Speed Reduction)

Db = u12-u22

30 (f + G)

  • Passing Sight Distance (PSD)
  • Decision Sight Distance (DSD)
distances for analysis90
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.
distances for analysis design criteria
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.
distances for analysis design criteria93
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.
distances for analysis driver eye and object height
DISTANCES FOR ANALYSIS Driver Eye and Object Height

H1 = driver eye height

H2 = object height

S = stopping sight distance

distances for analysis skid mark velocity estimates
DISTANCES FOR ANALYSISSkid 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

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

SHOCKWAVE THEORY

asce ymf pe review course97

ASCE YMF PE REVIEW COURSE

Transportation Planning

site impact analysis purpose

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.

site impact analysis when is a study needed
SITE IMPACT ANALYSISWhen 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 agency’s discretion
  • When development occurs in a sensitive area
  • When financial assessments are required
  • Clark County >300 peak hour trips
site impact analysis study area limits
SITE IMPACT ANALYSISStudy 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
site impact analysis study horizon
SITE IMPACT ANALYSIS Study Horizon
  • Anticipated opening day of major phases
  • Anticipated date of full build-out
  • Five years after full build-out
site impact analysis steps in the process
SITE IMPACT ANALYSISSteps 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
site impact analysis site traffic generation ite trip generation
SITE IMPACT ANALYSISSite Traffic GenerationITE Trip Generation
  • Select Rates or Equations
  • Identify Time Periods
  • Identify Day or Season
  • Correct for Mixed Use Developments
site impact analysis site traffic distribution methods
SITE IMPACT ANALYSISSite Traffic Distribution Methods
  • Analogy – Similar models
  • Trip Distribution Model
  • Surrogate Data - Local Knowledge
site impact analysis pass by traffic

SITE IMPACT ANALYSISPass-By Traffic

Traffic already on adjacent roadways that will be diverted to the new development

site impact analysis total area wide assignment
SITE IMPACT ANALYSIS Total Area Wide Assignment
  • Site Traffic
  • Non-site (Background)Traffic - Consider Design Year
site impact analysis site access improvements
SITE IMPACT ANALYSISSiteAccess 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
site impact analysis internal site circulation and parking requirements
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
site impact analysis internal site circulation and parking requirements cont
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
site impact analysis
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?

site impact analysis112
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

traffic safety roadway and roadside safety concepts
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
traffic safety an ideal highway
TRAFFIC SAFETYAN “IDEAL” HIGHWAY
  • Uniformly High-Quality Design
  • Avoid Discontinuities
traffic safety design influence on safety
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
traffic safety traffic safety analyses
TRAFFIC SAFETYTraffic Safety Analyses
  • Identification of High-Hazard Locations
  • Countermeasure Choices
  • Intersection Conflicts and Control
  • Roadside Designs
  • Color Codes
  • Taper Design
traffic safety identification of high hazard locations
TRAFFIC SAFETYIDENTIFICATION OF HIGH-HAZARD LOCATIONS
  • Crash Frequency
  • Crash Rate
  • Number-Rate
  • Equivalent Property Damage Only Rate
  • Rate Quality Control
  • Other Indicators
traffic safety crash frequency
TRAFFIC SAFETYCRASH FREQUENCY
  • Bias Towards Higher Volume Traffic Sections
  • Can Categorize Roadway Segments According to Functional Classification
traffic safety crash rate

SEGMENT CRASH RATE

TRAFFIC SAFETYCRASH RATE

Rseg = A x 105

(365 x T x V x L)

SPOT CRASH RATE

Rspot = A x 105

(365 x T x V)

traffic safety number rate
TRAFFIC SAFETYNUMBER-RATE
  • First Rank By Crash Frequency
  • Remove Locations Below Threshold Frequency
  • Re-Rank by Crash Rate
traffic safety equivalent property damage only epdo rate
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
traffic safety rate quality control
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%

traffic safety other non crash indicators
TRAFFIC SAFETYOTHER NON-CRASH INDICATORS
  • Pavement Skid Testing
  • Evidence of Evasive Actions
  • Capacity Deficiencies
  • Number of Access Points
  • Traffic Conflicts Analysis
traffic safety analysis of high hazard locations
Left-Turn/Head On

Right Angle

Rear-End

Sideswipe

Pedestrian

Bicycle

Run-Off-The Road

Fixed Object

Head-On

Parked Vehicle

Animal

Others

TRAFFIC SAFETYANALYSIS OF HIGH-HAZARD LOCATIONS

PATTERNS:

traffic safety collision diagram
TRAFFIC SAFETYCOLLISION DIAGRAM
  • Direction of Travel and Intended Maneuvers
  • Non-Contact Vehicles Involved
  • Date, Day of Week and Time of Day
  • Unusual Conditions
traffic safety selecting countermeasures
TRAFFIC SAFETYSELECTING COUNTERMEASURES
  • Countermeasure Should Provide Greatest Benefits Relative to Costs
  • Not All Problems Can Be Solved (3 E’s)
  • Full Range of Alternatives Should Be Considered
  • Evaluate Effectiveness of Improvements
traffic safety prioritization of improvements
TRAFFIC SAFETYPRIORITIZATION OF IMPROVEMENTS
  • Based On:
    • Funding
    • Project Costs
    • Crash Reduction Benefits
traffic safety improvement project planning
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
traffic safety implementation of projects
TRAFFIC SAFETYIMPLEMENTATION OF PROJECTS
  • Implement as Quickly as Practicable
traffic safety evaluation of implemented projects
TRAFFIC SAFETYEVALUATION OF IMPLEMENTED PROJECTS
  • Provides Information to Improve Future Decision-Making
  • Learn From Success (or Failure) of Implemented Projects
traffic safety
TRAFFIC SAFETY
  • Example

How many conflict points are there for a two-way, unsignalized, “T” intersection?

traffic safety hierarchy of intersection control
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
traffic safety warrants aashto mutcd

TRAFFIC SAFETYWarrantsAASHTO & MUTCD

Uncontrolled Intersections

Sight Distance

Yield or 2-way Stop

Priority

Multi-way Stop

Volumes

Crashes

traffic safety traffic control signals
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
traffic safety traffic control signals139
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
traffic safety mutcd signal warrants
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
traffic safety roadside cross section elements
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.
clear zone widths
Clear Zone Widths

Source: Roadside Design Guide (1996)

traffic safety signage striping colors
TRAFFIC SAFETYSignage / Striping Colors
  • Black—regulation
  • Blue—road user services guidance, tourist information, and evacuation route
  • Brown—recreational and cultural interest area guidance
  • Coral—unassigned
  • Fluorescent Pink—incident management
traffic safety signage striping colors144
TRAFFIC SAFETYSignage / Striping Colors
  • Fluorescent Yellow-Green—pedestrian warning, bicycle warning, playground warning, school bus and school warning
  • Green—indicated movements permitted, direction guidance
  • Light Blue—unassigned
  • Orange—temporary traffic control
  • Purple—unassigned
  • Red—stop or prohibition
  • White—regulation
  • Yellow—warning
traffic safety pedestrian level of service
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
traffic safety pedestrian level of service148
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 < Flow Rate < 10 p/min/ft

traffic safety pedestrian level of service149
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

contact information
CONTACT INFORMATION

Molly O’Brien, P.E.

Kimley-Horn and Associates, Inc.

702.862.3636

Molly.obrien@kimley-horn.com

Special Thanks to:

Paul Vilaluz, P.E., PTOE

Martin and Martin