After Evans: Working on an Approximation of a Combined Equilibrium Model Based on Precision Assignment May, 2011 TRB Planning Applications Conference, Reno, NV Presented by: Thomas Walker, Wolfgang Scherr, Chris Puchalsky DVRPC, Office of Modeling and Analysis
Motivation Objectives We need combined equilibrium Consistent agreement of model inputs and outputs: Travel time input for trip distribution and mode choice SHOULD EQUAL Congested travel time output from highway assignment Elimination of “model noise” in scenario comparison We need combined equilibrium Equilibrium in highway assignment alone is not enough Equilibrium of the entire system is needed How to achieve it with an iterative travel model: Iteration of the 4-stage-model Feedback Averaging of travel impedance between iterations
DVRPC’s Regional Travel Model TRANPLAN Model Migrated from UTPS (1980) Evans implementation (2000): Fixed weights for first 2 feedback iterations Calculation of optimal weights for 5 remaining iterations TIM 1.0 – in use since 2010 Migrated from TRANPLAN to VISUM Equilibrium method: Precision hwy assignment (path-based) Averaging of the impedance matrix between model iterations Simplified by constant weights (50/50)
Search for Optimal Solutions Feasible Solutions as Ordered by Weighting Routine 5 10 15 20 25 30 35 40 S 1 Objective Function Value
TIM 1.0 – Elimination of “Noise” TRANPLAN TIM 1.0 Network change
TIM 1.0: Model Convergence Run Time RAM Processor Speed Cores 4.5 hr 48 GB 2.67 GHz 16 5.5 hr 16 GB 2.4 GHz 8 Model termination if 3 criteria are met: Highway assignment Relative gap < 0.0001 Difference in highway trip matrx %RSME < 0.5 Difference in hwy impedance matrix %RSME < 0.1 Relative Gap
Conclusions and Summary Evans Mathematically great Implemented only in TRANPLAN Not supported in newer precision assignment software Alternative: feedback with constant weights Provides excellent convergence with reasonable computation time Good experience in DVRPC’s TIM 1.0 Future perspective – research needed Measuring combined equilibrium New “Evans” within precision highway assignment Convergence of microscopic activity-based models (ABM)