Cervenka NCTCOG IOWA PeerReview

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Travel Demand Modeling At NCTCOG: 

Travel Demand Modeling At NCTCOG Presentation For IOWA TMIP Peer Review March 30 – April 1, 2004


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Total Population Within The Dallas – Fort Worth Metropolitan Planning Area

Four-Step TRANSCAD Modeling Process: 


Transition To Reality: 

Transition To Reality Actual Scope Of Human Behavior  Model Scope All Person Trips  Motorized Person Trips All Travel Purposes  HBW, HNW, NHB, And Truck Purpose Categories All Occupations  Basic, Retail, And Service Jobs All Households  Income And Household Size Categories (Plus Auto Ownership Breakdowns) All Streets  Non-Local Streets Individual Data  Aggregate Data (Zones)



Roadway Preparation: 

Roadway Preparation Link Free Speed (Based On Speed Limit, Distance, Area Type, Functional Class, And Intersection Control) Directional Hourly Capacity (Based On Lanes, Area Type, Functional Class, And Divided/Undivided Designation) Time Period Capacity AM Peak, PM Peak, And OffPeak

Trip Generation: 

Trip Generation GISDK Macro Language Seven “Regular” Internal-Internal Trip Purposes 4 HBW, 1 HNW, 1 NHB, And 1 Truck Inputs Population, Households, Income, And Basic/Retail/Service Jobs Special Generators (Shopping Malls, Colleges, Hospitals, Airports)

Household Income Distribution: 

Household Income Distribution Total = 1 0.11 0.13 0.19 0.57

Household Size Distribution: 

Household Size Distribution

Demographics For Special Generators: 

Demographics For Special Generators Current Special Generators Regional Shopping Malls With Over 500,000 Square Feet (20) Colleges/Universities With Over 1,500 Enrolled Students (27) Hospitals With Over 300 Service Employees (42) DFW And Love Field Airport Terminals (Special Treatment) Special Input Data Fields (e.g., For Shopping Malls) SGRETAIL = Number of Jobs In Zone That Relate To The Shopping Mall SGUNIT = Total Leasable Square Footage (Thousands Of Square Feet) HBW, HNW, NHB, And Truck Trip Rates Per Thousand Square Feet

External Station Trip Tables: 

External Station Trip Tables Internal-External And External-Internal (IE/EI) Weekday Passenger Vehicles (Total Trip Ends) External-External (EE) Weekday Passenger Vehicles IE/EI Weekday Trucks (Six Or More Tires) EE Weekday Trucks (Six Or More Tires)

Mode Choice Inputs: 

Mode Choice Inputs Auto Travel Roadway Travel Time Roadway Length (Operating Cost) Daily Parking Cost Transit Travel In-Vehicle Transit Travel Time (Includes Dwell) Walk (Or Drive) Access Time Walk Transfer And Egress Time Initial And Transfer Wait Time Transit Fare Market Segment And Area Type Constants

Market Segmentation: 

Market Segmentation Objective: To Account For Differences In Commuter Behavior Segmentation Basis (6 HBW And 6 HNW) Household Income (3) Low Medium High Vehicle Availability For A Household (2) Vehicles Less Than Persons Vehicles Greater Than Or Equal To Persons

HBW Mode Choice: Mainframe vs. TRANSCAD: 

HBW Mode Choice: Mainframe vs. TRANSCAD Choice Drive Alone Shared Ride 3+ Shared Ride 2 Transit Drive Transit Walk Choice Drive Alone Shared Ride 3+ Shared Ride 2 Transit Drive Transit Walk Auto

HNW Mode Choice: Mainframe vs. TRANSCAD: 

HNW Mode Choice: Mainframe vs. TRANSCAD Choice Drive Alone Shared Ride 2+ Transit Drive Transit Walk Choice Shared Ride 3+ Shared Ride 2 Transit Drive Transit Walk Shared Ride Drive Alone Transit Drive

NHB Mode Choice: Mainframe vs. TRANSCAD: 

NHB Mode Choice: Mainframe vs. TRANSCAD Choice Drive Alone Shared Ride 2+ Transit Drive Transit Walk Choice Drive Alone Shared Ride 3+ Shared Ride 2 Transit Drive Transit Walk

Transit Assignment: 

Transit Assignment Four Multi-Path (Pathfinder) Production-Attraction Assignments For All HBW Transit Trips Peak Transit-Initial Drive Access (Park-and-Ride) Peak Transit-Initial Walk Access (No Park-and-Ride) For All HNW And NHB Transit Trips Offpeak Transit-Initial Drive Access (Park-and-Ride) Offpeak Transit-Initial Walk Access (No Park-and-Ride)

Traffic Assignment Preparation: 

Traffic Assignment Preparation PA To OD Trip Table Transposing, Time-Of-Day Factoring, And Aggregation Of Trip Purposes AM Peak Period (2.5 Hours) PM Peak Period (3.5 Hours) Off Peak Period (18 Hours) K Factoring Of OD Trip Tables (Post Mode Choice) Compensate For Gravity Model Limitations OD Estimation Procedure To Help With Problem Identification Adjustments/Checks Based On Screenline Results

Traffic Assignment: 

Traffic Assignment User Equilibrium Generalized Cost (Three 30-Iteration Assignments) A.M. Peak (6:30a – 8:59a: 2.5 hours) P.M. Peak (3:00p – 6:29p: 3.5 hours) OffPeak (18 hours) Four Vehicle Classes Loaded Simultaneously Drive Alone Shared-Ride “Sees” HOV Lanes Shared-Ride “Doesn’t See” HOV Lanes Trucks (Vehicles With 6 Or More Tires)

Speed vs. V/C Ratio (Example): 

Speed vs. V/C Ratio (Example)

Traffic Model Limitations: 

Traffic Model Limitations Ideally, the peak and offpeak congested speeds directly from traffic assignment should be used in trip distribution—but we “post process” because the assignment-calibrated parameters do not give us realistic speeds Related to above: “Peak Spreading” is not directly considered; in the future, we may consider peak hour and “shoulder of the peak” assignments We have no observed data to directly calibrate HOV-Toll usage; instead, we have to rely on our separately-calibrated HOV modeling and “toll road value of time” modeling

Traffic Model Limitations (Cont.): 

Traffic Model Limitations (Cont.) The Offpeak assignment represents 18 hours of the day—perhaps a future breakdown into Mid-Day Offpeak (9:00 a.m. – 2:59 p.m.) and Evening/Night Offpeak (6:30 p.m. to 6:29 a.m.) All passenger vehicles are assumed to have the same value of time

Calibration/Validation Issues (Transit): 

Calibration/Validation Issues (Transit) Reasonableness Of Peak and Offpeak Transit Speeds Used In Skimming For Mode Choice (Observed And Future) Coded vs. Observed Bus And Train VMT Modeled vs. Observed Weekday Riders By Bus Route And Rail Route (Route-Level RMSE And Percent Error) Modeled vs. Observed Weekday Rail Station Boardings (Station-Level RMSE And Percent Error) Reasonableness Of Modeled vs. Observed Mode Of Access Distributions To Individual Rail Stations

Calibration/Validation Issues (Traffic--Slide 1): 

Calibration/Validation Issues (Traffic--Slide 1) Current And Future-Year Reasonableness Of Roadway Speeds Used In Skimming For Trip Distribution And Mode Choice Reasonableness Of Modeled vs. Observed Percent Intrazonal Trips By Trip Purpose (DFW = 1.5% For HBW; 8.7% For HNW; 9.3% For NHB; And 0.5% For Trucks) Reasonableness Of Modeled vs. Observed Average Person Trip Lengths (Or Trip Length Frequency Distributions) By Trip Purpose, For Interzonal Trips Modeled vs. Observed Weekday Link Volumes By Functional Class (RMSE And Percent Error)

Calibration/Validation Issues (Traffic—Slide 2): 

Calibration/Validation Issues (Traffic—Slide 2) Modeled vs. Observed Weekday Screenline Volumes (Overall Magnitude And % Error); DFW = 1262 Links On 89 Screenlines Modeled vs. Observed AM Peak, PM Peak, And OffPeak Auto And Truck VMT By Functional Class (% Error) Check Very High And Very Low AM, PM, And OffPeak V/C Ratios Checks Of The “Hundred Largest Link Errors” Report Magnitude And % Error

Calibration/Validation Issues (Traffic—Slide 3): 

Calibration/Validation Issues (Traffic—Slide 3) “True” Validation Requires Calibration Sensitivity Tests AND Forecast Sensitivity (Or Sensibility?) Tests Calibrated Model “Backcast” Checks Would Be Nice, Although Historical Model Validity Is Still No Guarantee Of Forecastability Individual Capacity-Per-Lane Changes To Improve Validation? No, But Consider More Functional Classes Keep In Mind The Prime Objectives For Modeling Link-Specific Changes Are Problematic For New Links

Calibration/Validation Issues (Traffic—Slide 4): 

Calibration/Validation Issues (Traffic—Slide 4) Individual Link Speed/Impedance Changes To Improve Validation? No, But Check Speed Limits And Functional Class Check Reasonableness Of Free And Congested Speeds Try To Find The Underlying Cause Change Centroid Connectors To Improve Validation? Sure (But Apply Modifications In Some Logical Manner) Don’t Forget “Forecastability” Of The Connectors Caution On Zone Sizes Factor Trip Tables To Improve Screenline Validation Results? Yes—But Exercise Due Caution On Forecastability Not Theoretically Elegant! Check First For Trip Generation Problems

Recommendations For Model Applications Work At NCTCOG: 

Recommendations For Model Applications Work At NCTCOG Every Modeling Study Needs “Direct Oversight” By A TransCAD Model Applications Champion -- So, What Is A Champion? Is Very “Hands-On” Experienced With TransCAD We Can Test People On This, Too! Has A Good Understanding Of GIS And Travel Model Theory Maybe We Should Give An Oral Certification Test! …And (Ideally) Spends Over 70% Of His/Her Time On Model Applications Work

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