developing a sketch plan model for the southern california association of governments

Developing a Sketch Plan Model for the Southern California Association of Governments

Jim Lam, Caliper CorporationGuoxiong Huang, SCAG

Mark Bradley, BB&CRich Kuzmyak

Hong KimTRB Applications Conference, May 18, 2009

Outline

• Goal of the Sketch Plan Model Project• Sketch Plan Model Simplifications• Zonal Aggregation Models• Other Sketch Plan Features• Sketch Plan Demo• Model Run Times• Calibration Results• Future Work

Goal of the Sketch Plan Model Project

• Current Regional Model is 4000+ zones and takes 24 hours to run

• To create a sketch planning version of the regional travel demand model

• Tool will be a quick response tool for testing a wide range of policies and projects to assess their benefits for the region.

• Tool will be simpler to run, much faster in execution, but be sufficiently accurate to identify beneficial projects for further detailed analysis with the full model.

• Keep model code consistent with Regional Model

Sketch Plan Model Simplifications

• Aggregate TAZs to a simpler zonal structure

• Option to “skip” major portions of the model, such as transit

• Reduce input and output files, and reduce user-controllable model parameters

• Create a simplified interface• Reduce feedback loops and one-loop

model run• Simplify networks*• Mode split simplification*• Trip purpose reductions*• Vehicle ownership category

reductions** Models considered but ultimately not adopted

Zonal Aggregation Models

• Zones reduced from 4109 to 302 zones, networks remained the same size

• Network centroid connectors realign to “Superzones” and networks re-skimmed for 302 zone system

• Extra models necessary to account for aggregation bias and for trip loss during aggregation (Zonal Allocation and Zonal Aggregation Models)

Example of Network Realignment

Zonal Aggregation Models• Zonal Allocation Model to determine

best “skim” for aggregated OD pair• Random choice model

• Randomly chosen OD pair from Regional skims for consistency with Regional estimations

• Problem: Need more than one random chosen pair to reduce variability, which reduces performance

• Randomness causes variability of results in alternatives analysis

• Weighted zonal allocation model• Superzone centroid location is chosen based

on HH and Emp weights allTAZ

iallTAZ

ii HouseholdHouseholdLongitudeLongitude /*

allTAZ

iallTAZ

ii HouseholdHouseholdLatitudeLatitude /*

allTAZ

iallTAZ

ii EmploymentEmploymentLongitudeLongitude /*

allTAZ

iallTAZ

ii EmploymentEmploymentLatitudeLatitude /*

Zonal Aggregation Models

• Intra-Superzone Trips Model • To account for underassignment of

trips

This Trip

Becomes an Intrazonal Trip

Zonal Aggregation Models

• Intra-Superzone Trips Model • Divide OD trips into Inter-

Superzone and Intra-Superzone trips from original correspondences

• Expand Intra-Superzone trips into original TAZ trip matrix using base OD matrices and IPF

• Separately assign Inter-Superzone trips and Intra-Superzone trips

Intra-Superzone Assignment ExampleAggregate OD Matrix Inter-Superzone

TripIntra-Superzone Trip

Correspondence Table Disaggregate Intra-Superzone Trip

Zonal Aggregation Models

• Superzone Connector Assignment • To better assign Inter-Superzone

Trips

Should really be thisShould really be this

This TripThis Trip

Other Sketch Plan Features

• Automatically create Sketch Inputs from Regional Inputs

• Provide a simple interface• Simply define alternative scenarios• Simply run and compare multiple

scenarios

Demo of Sketch Plan Model

Model Run Times

• Regional Model – 24 hours• Full Sketch Plan Run – 2 hours• One-loop highway-only run – 75

minutes

Calibration Results

Calibration Results

Future Work

• Explore Random allocation of zones for skimming

• Add transit-only component• Integration with TDM and land use

models• Additional optimization

Thank You