I teamed up with Craig Raborn, Nicholas Institute‘s transportation policy analyst, and developed a U.S. transportation model called SIMTrave (Sequenced Integrated Model of Transportation Activity, Vehicle, and Emissions).
The model is capable of estimating transport demand and emissions, as well as simulating the impacts of policy and technological measures in transport-related sectors, covering all transport modes from the 50 states in the U.S. continent up to 2030.
1. Model Development
While Craig used his extensive experience and wealth of knowledge in transportation research and policy to design the model and to perform data collection, I used my skill sets in economic modeling, general programming, and GAMS programming to develop and debug the model.
While we developed the model, I have to admit that Craig and I were a little bit carried away. We were both so very excited and committed to the design and development that we kept working through the Christmas Holiday of 2009. We even exchanged emails right during the New Year’s Day overnight shift (see the image below).
At that time, Craig and I definitely had a blast calibrating the GAMS model. (But I am not sure if our respective spouses shared the same sentiment. I am hoping Diny, my wife, and Dana, Craig’s wife, do not read this blog entry. 🙂 )
2. Based on European TREMOVE
SIMTrave development was based on a partial equilibrium European transport model called TREMOVE which is written in GAMS, Microsoft Access, and Microsoft Excel VBA.
3. Four Modules
SIMTrave analysis is done through four interrelated modules: Demand, Fleet, Emission, and Welfare.
- The transport demand module (DEMAND)
- The vehicle fleet module (FLEET)
- The environmental module (MOVES)
- The welfare module (WELFARE)
The four modules are linked together, i.e. they exchange information in order to provide a consistent picture of the different aspects modeled.
For road vehicles, emission factors are based upon the MOVES Emission calculation (developed by EPA) with several improvements made and included in the current SIMTrave model. Fuel consumption and emission factors for diesel trains and aircraft (by distance class) have been derived from the TRENDS database. For electric trains, trams, and metros only total energy consumption (in kilowatt-hours) is calculated in this module.
4. Constant of Elasticity of Substitution (CES) Tree Design
The SIMTRAVE partial equilbrium is based on Constant Elasticity of Substitution (CES) type of aggregator function which combines two or more types of consumption, or two or more types of productive inputs into an aggregate quantity. Following the European design, the CES trees is divided into consumer travel and production travel on the upper level. The trees are divided furthermore into urban and non-urban on the lower level. Craig cleverly adjusted the CES trees to reflect the U.S. transportation condition.
5. Sample Analysis
We tested SIMTrave by putting in an economic shock of oil price increase (both gasoline and diesel) in 2010.
SIMTrave output shows that there is a specific effect of oil price increase for different vehicle types. In general, the amount of vehicles miles traveled decreases and the amount of vehicle purchases (varies with price) also decreases.
When we saw that the output of SIMTrave showed the right economic behavior, Craig and I felt that the hard work of long hours of model design, development, debugging, and calibrating finally paid off.
After the completion of SIMTrave development, Craig has continued to intelligently tweak the model (which I have not been involved with since I have been fully occupied with OptimaCCS development).
I want to thank Craig for sharing with me both his passion for, and deep knowledge of, transportation policy. His strong expertise in transportation research played a large part in the success of SIMTrave development. I am not a transportation expert. But I did enjoy working with him in coding the transportation model in GAMS.
Anyone interested in knowing more about SIMTrave or transportation policy in general can contact Craig Raborn.
Darmawan Prasodjo, PhD