Transportation Planning

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Transportation Planning
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What is a Traffic Model?

• Typical Definition
• A computer program that runs mathematical
  equations using input data to replicate travel
  choices that individuals make
• The output is a measure of future travel demand
  that is expressed in terms of future traffic
  volumes.
• Simply A forecast of future travel
• Where are people traveling to and from
• What routes are they choosing to get there

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Why are Models Important?

• Models are the heart of Transportation Planning
• They help us determine how much traffic will be
  on our roadways in the future
• They help us to understand the impact that
  development has on our transportation system
• They guide future investment strategies
• Models allow us to make informed decisions.

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What Are Travel Models Used For?

• Provide the best possible information about
  future needs
• Determining where congestion may be in the future
• Determining what projects will alleviate or
  minimize that congestion.
• Scenario analyses (What ifs)
• How many lanes are we going to need?
• Determine traffic impact due to land use changes

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Example Scenario

• Planner or Engineer
• Finite in available funding
• Your job ID what roadway projects will be in the
  MPO Transportation Improvement Program
• Resources are scarce
• Choices need to be good ones
• Public drives the roads every day and are ready
  to complain
• How do you go about selecting solutions?
• Use the travel demand model to aid in determining
  how to address existing congestion problems.
• Test various projects to determine effectiveness
• Measure in VMT and VHT savings

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Travel Demand

• Why did the chicken cross the road?
• Duh -- to get where they want to be???

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Why Do People Travel?

• Hence, the truism that Travel is a derived
  demand -- i.e. the demand for travel is derived
  from the demand for spatially-separated
  activities
• Corollary Travel is a disutility, that people
  try to minimize

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Travel

• Saved travel time is a benefit, hence a basis for
  valuing transportation improvements
• THE largest benefit component in most
  cost-benefit analyses
• We can reduce travel by
• ... making it more expensive
• congestion pricing, fuel taxes, parking pricing

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Travel

• We can reduce travel by
• bringing activities closer together
• increasing density and mixture of land uses
• using ICT (information and communication
  technology) to conduct the activity remotely
• telecommuting, -conferencing, -shopping,
  -education, -medicine, -justice

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But is that the only reason people travel -- to
get somewhere in particular?
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Why Would Travel be Desirable?

• Escape
• Exercise, physical/mental therapy
• Curiosity, variety-, adventure-seeking conquest
• Sensation of speed or even just movement
• Exposure to the environment, information
• Enjoyment of a route, not just a destination
• Symbolic value (status, independence)
• Buffer between activities, synergy with multiple
  activities

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Trends In Travel Demand
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Global Changes, 1960-1990
NAM N. America LAM Latin America WEU W.
Europe EEU E. Europe FSU Former Soviet
Union MEA Middle East and North Africa AFR
Sub-Saharan Africa CPA Centrally Planned Asia
and China SAS South Asia PAS Other Pacific
Asia PAO Other Pacific OECD
                                                
                                                  
                                                  
                                                  
       
Motorized mobility (pkm) per capita, 1960 and
1990. Source Schafer, 1998
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Avg. Annual Growth Rate of Cars and Their Use,
1970-90
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Mobility as a Function of GDP
NAM N. America LAM Latin America WEU W.
Europe EEU E. Europe FSU Former Soviet
Union MEA Middle East and North Africa AFR
Sub-Saharan Africa CPA Centrally Planned Asia
and China SAS South Asia PAS Other Pacific
Asia PAO Other Pacific OECD
                                                
                                                  
                                                  
                                                  
       
Motorized mobility (car, bus, rail, and aircraft)
per capita by world region vs GDP per capita,
between 1960 and 1990. Source Schafer, 1998
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Car Ownership vs. GDP
                                                
                                                  
                                                  
                                                  
       
SAS South Asia PAS Other Pacific Asia CPA
Centrally Planned Asia and China
Estimated motorization rates for CPA, PAS and
SAS, compared with the observed rise in
motorization in several countries. Source of
historical data United Nations, 1960 United
Nations, 1993a and IRF, various years. Source for
figure Schafer and Victor, 2000
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Projected Mobility, 2050
                                                
                                                  
                                                  
                                                  
       
Historical and estimated future total global
mobility by mode in 1960, 1990, 2020 and
2050. Source Schafer and Victor, 2000
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The 4 step transport planning process

• OUTPUT
• Estimated trips
• Estimated modal shares
• Estimated travel speeds
• Estimated travel delays
• Air Quality

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Inputs- Demographic Data

• Household size
• Income level
• Autos per
• household
• Age

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Inputs- Transportation Systems

• Most streets, all highways
• Parking
• Public Transportation
• Speeds, travel times, and speed limits
• Traffic volumes
• Transit ridership and fares
• Vehicle occupancy

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Inputs- Land Use

• Current land use and zoning
• Activity for each area
• Land use and zoning plans
• Base maps and topography

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Land Use

• Definition Spatial pattern of different economic
  uses of land
• Residential
• Industrial
• Commercial
• Institutional
• A component of the urban system
• Defines, at least in part, the personality of a
  city

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Land Use

• Urban form spatial arrangement of built
  environment elements and urban activities
• Density
• Homogeneity
• Concentricity
• Connectivity

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Transportation-Land Use Connection

• Changes in location, type and density of land use
  affects travel choices and patterns
• Past transportation decisions evident in todays
  development patterns

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Transportation-Land Use Connection
Land Use
Trips
Transportation Needs
Land Value
Transportation Facility
Accessibility
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Accessibility

• Ease of movement between places
• Can be assessed separately for different modes,
  purposes, etc.

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Urban Sprawl

• Sprawl is random unplanned growth characterized
  by inadequate accessibility to essential land
  uses such as housing, jobs, and public services,
  i.e., schools, parks, and mass transit

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Urban Sprawl

• Sprawl is directly identified with urban growth-
  as cities get bigger, they expand around their
  peripheries
• Big cities are attracting population.. But
  population is being added to the edge at lower
  densities and the dominant transport is the car,
  for ease of access
• Population and other activity is also
  decentralizing very fast to lower density suburbs

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Results of Sprawl

• More Vehicle Miles Traveled (VMT)
• Longer Travel Times
• Greater Number of Auto Trips
• Less Cost-Effective and Efficient Transit

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Building a Travel Demand Model

• DATA
• Population (how many people do we have?)
• Households (where do they live)
• Employment (jobs, shopping, restaurants,
  recreation, etc.)
• Schools and college locations
• Roadway Network TAZ (traffic analysis zones)

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Traffic Analysis Zones (TAZ)

• Used to represent transportation demand
• Design guidelines
• equal size
• homogeneous land use (residential, retail,
  industrial, etc)
• not crossed by network or physical barriers
• Trip assumed to originate from a single point
  (centroid)

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TAZ Characteristics

• TAZ boundaries are major roadways or physical
  barriers such as railroads, rivers, airport
  boundaries etc.
• Typically follow block or block group boundaries
• Goal replicate areas of Origin and Destination
  for trips being made.
• Home to Work Home to Shopping Work to
  Shopping, etc

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TAZ Characteristics

• Zones are characterized by their population,
  employment, and other factors
• They are the places where trip making decisions
  are made (trip producer) and the trip need is met
  (trip attractor)

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Traffic Analysis Zones
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TAZ Characteristics contd

• Simple representation of the geometry of the
  transportation systems (usually major roads or
  transportation routes)
• Links sections of roadway (or railway)
• Nodes intersection of 2 links
• Centroids center of TAZs Trip making is
  assumed to begin at the zone centroid
• Centroid connectors centroid to roadway network
  where trips load onto the network

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Trip Generation

• Decision to travel for a specific purpose (e.g.
  eat lunch)
• -HOW MANY TRIPS??

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Trip Generation

• Defines the relationship between trip-making,
  socio-economic characteristics, and land use
  activities
• Purpose
• Predict how many trips will be made
• Predict exactly when a trip will be made

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Trip Purposes
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Trip Generation

• Methods
• Cross Classification
• Regression Analysis Linear relationship

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Cross-Classification

• Households in TAZs aggregated into groups
• Rates for each group used to determine the number
  of trips.
• Trip rates based on household characteristics
  (income level, vehicle ownership, household size,
  )

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Cross-Classification Method (cross-classification
rates)
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Regression Analysis

• Allows multiple variables and nonlinearity
• The number of trips f (population, autos,
  number of dwelling units, )
• The trip predictors (population, autos, ) need
  to be independent

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Trip Distribution

• Choice of destination (a particular restaurant?
  The nearest restaurant?)
• -Given a location, where do people go to satisfy
  demand for an activity type?
• -Determine origin and destination of trips

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Trip Distribution
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Gravity Model
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Trip Distribution-Gravity Model
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Trip Distribution

• f(D) travel impedance can be a function of
  distance, time, or user cost. Usually use time.

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Trip Distribution
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Trip Distribution
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Mode Choice

• How do people use the transport system?
• What modes do they choose
• (transit, walk, carpool, drive alone,)?
• How do they react to varying
• transport service quality?

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Mode Choice
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Mode Choice

• Travel Time
• In-vehicle time
• Walk, wait and drive access
• Travel Cost
• Auto operating, transit fares, parking, tolls,
  etc.

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Trip / Traffic Assignment

• How do people use the transport system?
• Given a mode, which route do they choose (e.g.
  E-5..)?
• Which parts of the transport system do they use?

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Path Selection Criteria

• The driver wants to minimize impedance..
• Composite index of travel impedance
• normally includes
• Travel Time
• Trip Cost
• Out of pocket costs
• Tolls
• Turn Penalties Prohibitions
• (e.g., no left turn)

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Trip Assignment Models

• All-or-Nothing Assignment
• User Equilibrium Assignment
• System Optimum Assignment

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All-or-Nothing Assignment

• Trips are assigned on the shortest route which is
  the minimum travel time or cost
• Simple and inexpensive to perform
• Does not take account of congestion effect
• Disadvantage
• Assumes all traffic will travel on shortest path
• Creates unrealistic flow patterns

Step 1 Find shortest route between the TAZs
Step 2 Assign all trips to links comprising
shortest route
Step 3 Continue until trips between all TAZ
pairs have been assigned
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User Equilibrium Assignment

• User equilibrium problem formulated by Beckmann
  et. al.(1956) can be solved using Wardrops First
  condition
• For each O-D pair, at user equilibrium, the
  travel time on all used paths is less than or
  equal to the travel time that would be
  experienced by a single vehicle on any unused
  path.
• Thus, at equilibrium, no one can reduce his or
  her travel cost by choosing another choice set.

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System Optimum Assignment

• Social Equilibrium principle
• Traffic should be assigned in a congested network
  in such a way that the total system travel cost
  is minimized
• It is more of a design principle for transport
  planner and engineers