an Iowa State University center SIMPCO Traffic Modeling Workshop Presented by: Iowa Department of Transportation and Center for Transportation Research and Education (CTRE) Thursday, February 17, 2000 Sioux City, Iowa

an Iowa State University center Workshop Overview intro to traffic modeling overview of model components model inputs break the 4 steps model outputs validation and model errors future of traffic modeling Sioux City model and GIS interface

an Iowa State University center Why are we here today?

an Iowa State University center Traffic Modeling Goals understand impact of transportation investments on mobility and accessibility understand impact of development on transportation system part of providing continuous, comprehensive and coordinated planning activities in summary … foster efficient transportation investments

an Iowa State University center What can a model tell me?

an Iowa State University center What else can a model be used for? Evaluating projects in TIP evaluating the long range transportation plan predict future travel evaluate impacts of development provides input to air quality and noise analysis assess transit alternatives (if modeled) assess social initiatives (welfare to work, environmental justice) planning for highway safety

an Iowa State University center Introduction to Travel Forecasting Video

an Iowa State University center Traffic Modeling History Aggregate (zone) models Detroit/CATS Planpac/UTPS PC packages (Tranplan, etc.) future: activity based, microsimulation? Source: NTI

an Iowa State University center inputsoutputs What the model needs What you get from the model! How the model works model Opening the “black box”

an Iowa State University center The Partnership Inputs –Landuse planners, MPO planners, DOT (external, primary) Model –MPO planners, consultants, DOTs, univ. Outputs –decision makers (MPO, business, elected officials, …)

an Iowa State University center Workshop Overview intro to traffic modeling overview of model components model inputs break the 4 steps model outputs validation and model errors future of traffic modeling Sioux City model and GIS interface

an Iowa State University center Traffic Modeling How the modules work together Source: NTI Land Use, Population & Employment Traffic Analysis Zones (TAZs) Trip Generation Trip Distribution Mode and Path Choice Modal Trip Tables Auto Occupancy P/A to O/D Land Use Models Travel Pattern Surveys Transit Assignment Highway Assignment Speeds Vehicle Emissions Estimates Transportation Facilities and Performance Highway and Transit Networks Skim Trees (Shortest Paths) A A A A

an Iowa State University center Workshop Overview intro to traffic modeling overview of model components model inputs break the 4 steps model outputs validation and model errors future of traffic modeling Sioux City model and GIS interface

an Iowa State University center Typical Inputs population and employment by –age –economic level –vehicle ownership –family size –type of industry and occupations –past data for trends

an Iowa State University center Typical Inputs Land use –current land use and zoning –activity for each area –DU by type –past data for trends –land use and zoning plans –base maps and topography

an Iowa State University center Typical Inputs Transportation system –most streets, all highways –parking –public transportation –size, characteristics, conditions –use, cost, service levels –speeds and travel times, speed limits

an Iowa State University center Typical Inputs Transportation system (cont.) –traffic volumes –commercial vehicle volumes –transit ridership and fares –vehicle occupancy

an Iowa State University center Typical Inputs Travel patterns –description and characteristics of trips within into through the study area –number of trips and purpose –origins and destinations (OD) –mode use

an Iowa State University center Land Use - Transportation Relationship residential development commercial development transportation improvement click here for video

an Iowa State University center Sources of Data Census/CTPP aerial photos state employment office state franchise tax board Traffic counts building permits utility company records studies (observation) surveys

an Iowa State University center Surveys - Common Types of Surveys Used Home Interview Survey –US Census Journey to Work –National Personal Transportation Survey –Local Surveys Cordon O&D Survey Expressed Preference Survey –transit –employees

an Iowa State University center click here for video

an Iowa State University center Break time

an Iowa State University center Workshop Overview intro to traffic modeling overview of model components model inputs break the 4 steps model outputs validation and model errors future of traffic modeling Sioux City model and GIS interface

an Iowa State University center The “Four-Steps” Network Building - computer representation of your city (not a step!) Trip Generation - How many trips? Trip Distribution - Where are they going? Mode Choices - By what mode? Trip Assignment - What path are they taking?

an Iowa State University center Network Building - Traffic Analysis Zones Used to represent transportation demand Design guidelines –equal size –homogeneous land use –not crossed by network or physical barriers Trip assumed to originate from a single point (centroid)

an Iowa State University center Network Building - Example Traffic Analysis Zones (TAZs)

an Iowa State University center Network Building - Representing the Street System A system of nodes, links, and centroids that describe a transportation system. 1. Node: intersections; also points of origin/destination of traffic 2. Links: Used to represent the street network (local roads are not included. 3. Centroids: special node representing origin and destination of all trips for TAZ. 4. Centroid connectors: special links that represent local roads and provide access to centroids

an Iowa State University center Network Building - Actual Street System

an Iowa State University center Network Building - Computer Street System Node Centroid 46 Centroid Connector Link Link Source: NTI

an Iowa State University center Network Building - Link Record

an Iowa State University center The “Four-Steps” Network Building - computer representation of your city (not a step!) Trip Generation - How many trips? Trip Distribution - Where are they going? Mode Choice - By what mode? Trip Assignment - What path are they taking?

an Iowa State University center Source: NTI Trip Generation

an Iowa State University center Trip Generation Methods Cross - Classification –Used to determine TAZ productions in regional models Rates Based on Activity Units –Used for Traffic Impact Analysis or very detailed regional models Regression –Used to determine TAZ attractions

an Iowa State University center Cross-Classification Method 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, … )

an Iowa State University center Source: NTI Cross-Classification Method - Example Cross-Classification Rates Table

an Iowa State University center Rates Based on Activity Units Method Rates provided by the Institute of Transportation Engineers (ITE) Rates based upon demographics (average household size, business type, number of employees …) ITE provides a trip generation software package

an Iowa State University center ITE Trip Generation Software

an Iowa State University center Regression Method 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

an Iowa State University center The “Four-Steps” Network Building - computer representation of your city (not a step!) Trip Generation - How many trips? Trip Distribution - Where are they going? Mode Choice - By what mode? Trip Assignment - What path are they taking?

an Iowa State University center Trip Distribution

an Iowa State University center Gravity Model

an Iowa State University center Source: NTI Trip Distribution - The Gravity Model

an Iowa State University center Trip Distribution f(D) can be a function of distance, time, or user cost. Usually use time.

an Iowa State University center Trip Distribution

an Iowa State University center Trip Distribution

an Iowa State University center The “Four-Steps” Network Building - computer representation of your city (not a step!) Trip Generation - How many trips? Trip Distribution - Where are they going? Mode Choice - By what mode? Trip Assignment - What path are they taking?

an Iowa State University center Mode Split

an Iowa State University center

Mode Choice Models none used in Iowa at present –number of trips smaller than error term –chicken and egg problem??? Diversion curves Logit Models

an Iowa State University center Source: NTI Mode & Path Choice - Models

an Iowa State University center Mode & Path Choice - Typical Decision Variables Travel Time –In-vehicle time –Walk, wait and drive access Travel Cost –Auto operating, transit fares, parking, tolls, etc. Transfers –1, 2, or 3 Source: NTI

an Iowa State University center The “Four-Steps” Network Building - computer representation of your city (not a step!) Trip Generation - How many trips? Trip Distribution - Where are they going? Mode Choice - By what mode? Trip Assignment - What path are they taking?

an Iowa State University center Trip Assignment - Path Selection Criteria Composite index of travel impedance which would normally include: Travel Time Trip Cost –Out of pocket costs –Tolls Turn Penalties & Prohibitions (e.g., no left turn) Source: NTI

an Iowa State University center Source: NTI Trip Assignment - Path Selection

an Iowa State University center Trip Assignment Several methods available –uncongested –human behavior –congestion model may have to be adjusted –bridges –freeways click here for more info

an Iowa State University center Workshop Overview intro to traffic modeling overview of model components model inputs break the 4 steps model outputs validation and model errors future of traffic modeling Sioux City model and GIS interface

an Iowa State University center Model Outputs Link volumes and speeds turning movements at intersections estimates of VMT (vehicle miles traveled) congestion measures all by category (jurisdiction, type of roadway, corridor, …)

an Iowa State University center Workshop Overview intro to traffic modeling overview of model components model inputs break the 4 steps model outputs validation and model errors future of traffic modeling Sioux City model and GIS interface

an Iowa State University center Steps to Obtain a Reliable Model Model Estimation Model Calibration Model Validation Model Application Reasonableness Checks Sensitivity Checks

an Iowa State University center EstimationCalibrationValidationApplication Validation and Reasonableness Checks Source:Barton-Aschman Model Validation Manual

an Iowa State University center Steps to Obtain a Reliable Model Model Estimation –Statistical estimation of model parameters Trip Generation Rates Trip Length Frequency Distribution Model Calibration –Adjustment of model parameters until predicted travel matches observed travel

an Iowa State University center Steps to Obtain a Reliable Model Model Validation –Checking the model results against observed data and adjusting the parameters until model results fall within an acceptable range of error. Model Application –Checking the reasonableness of future year traffic projections –Testing the sensitivity of the model to system or policy changes

an Iowa State University center Reasonableness Checks Trip Length Frequency Distribution Trip Generation Rates (What land uses generate what kind and number of trips? Total Regional Values (VMT, VHT) Sub-regional Values Logic Tests (Shortest Path)

an Iowa State University center Sensitivity Checks How the model responds to changes in: –Transportation System –Socioeconomic Data –Policy Changes (For base year and future year!) Expressed in the Elasticity of a variable –What happens to travel demand when gas prices triple? Or, parking costs decrease dramatically?

an Iowa State University center Connectivity Check

an Iowa State University center Screen Line

an Iowa State University center Cordon Line

an Iowa State University center Cut Line

an Iowa State University center Source: NTI Acceptable Ranges of Error

an Iowa State University center Highway Assignments - Level of Precision In general, assignments have been considered sufficiently accurate if to within +/- one lane of traffic. (More precision is being sought for air quality analysis) Intersection turning movements are beyond the reach of region travel models! (Local) Source: NTI

an Iowa State University center Workshop Overview intro to traffic modeling overview of model components model inputs break the 4 steps model outputs validation and model errors future of traffic modeling Sioux City model and GIS interface

an Iowa State University center Travel models … what’s next? Simultaneous models (1970s) dynamic models (ITS) activity-based models microsimulation models TMIP/Transims click here for video

an Iowa State University center Workshop Overview intro to traffic modeling overview of model components model inputs break the 4 steps model outputs validation and model errors future of traffic modeling Sioux City model and GIS interface

an Iowa State University center Original Visualization Tool HNIS

an Iowa State University center New Visualization Tool GIS Interface

an Iowa State University center GIS Interface Tools Access Time to any Point

an Iowa State University center GIS Interface Tools Turning Movements Display

an Iowa State University center GIS Interface Tools Shortest Path

an Iowa State University center Daily trips using bridge

an Iowa State University center Contact Info Reg Souleyrette – –

an Iowa State University center Trip Generation Checks SE Data Reasonableness –Zonal DU #’s correct? –Zonal Population correct? Household Income –Common dollar value over all analysis periods? Production/Attraction Rates –Sometimes rates are borrowed and out of date –Valid for model year?

an Iowa State University center Trip Generation Checks Special Generators –Trip rates are significantly different from standard trip rates. –Malls, Sporting Arenas, Airports, etc. Trip Balancing Factors –Balancing P’s and A’s checks the quality of SE data and trip rates –Ratio should be between 0.9 and 1.1

an Iowa State University center Auto Occupancy In modeling there is a conversion of person trips to vehicle trips Changes in auto occupancy can result in significant changes in trips By adjusting auto occupancy rates the vehicle trips can be adjusted up or down.

an Iowa State University center Trip Distribution Checks Powerful method for adjusting traffic volumes is in the distribution process. Mean Trip Length –Shortening or increasing the average trip lengths will in turn raise or lower traffic volumes. Estimation of Trip Length –Originally derived from OD studies in 1960’s

an Iowa State University center Traffic Assignment Checks Screen Lines –Extend completely across study area Cordon Lines –Completely encompass a designated area –CBD (Central Business District) Cut Lines –Extend across a corridor containing multiple facilities

an Iowa State University center Traffic Assignment Checks Link Volume vs Vehicle Count –Reasonable #’s? Centroid Connector Volumes Reasonable? –10, ,000 per day VMT (vehicle miles traveled system wide) VHT (vehicle hours traveled system wide)