Q&A
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General
1. Data, Data, Data… where and how do we get the segment and ramp data (even half-way decent) to drive the OPT tool with 70% (or better) level of confidence?
When we talk about the quality of simulation results, we must separate the simulation model and the data going into the model. If the data are bad or non-existent, any simulation model would fail. The model that OPT will be using is at least as good as FREQ: when we take the same input for FREQ and for the OPT model, the results are the same. We did this exercise at the time of the OPT proposal preparation.
Now, data… Data must be provided by the modeler (a person who builds and runs the model). PeMS is one possible data source. Others can include Census counts, manual data collection, or some demand model. OPT version 1 will have just means to input data, similar to other simulators, but it won’t have automatic data pulling from sources. A modeler would have to input the data in the OPT application window (e.g., copy/paste) or import a spreadsheet (or a CSV/TSV/Text file) in a given format. The input data format will be discussed with the user group.
2. FREQ uses 1965 HCS capacities… will OPT tool be updated to use latest 2016 HCS capacities?
Lane capacities will be user-settable parameters. Default values will also be user-settable. “Factory defaults” can be made to come from 2016 HCM.
3. Will the OPT tool handle dynamic pricing, or at least segregate 2+ HOV, from 3+ HOV, from FasTrak type SOV buy-on trips?
YES. Segregation of 2+, 3+ HOV and SOV will happen using different vehicle traffic types. HOT pricing will be handled by a controller with adjustable parameters.
4. Will the OPT tool be able to evaluate “non-lane addition” proposals.. such as ITS element packages for operations management, and TSM proposals, and TDM proposals?
YES. This is what OPT is primarily intended for. TSM e.g.: ramp metering, speed advisory, prioritization. TDM: OPT will assess the operational impact of demand change.
5. Will the OPT be able to export curvilinear files to lay on top of aerial imagery or design layouts? (using correct the geo-spatial locations)
Version 1.0 of OPT will not have this capability. Primarily, because making a road network editor compatible with GIS software is an undertaking too large for the scope of this project. However, understanding that this is a very useful feature, we will explore what can be done in terms of import/export of a road network with road shapes, and discuss possible options with the user group.
Modeling
1. Does OPT require that only balanced volumes be entered? In other words, if there is inconsistency between ramp volume counts and/or PeMS volumes at adjacent locations, must the user balance the volumes or will OPT do it internally?
OPT accepts any flows as long as they are non-negative. The modeler is responsible for the quality of the input data. Just like any other simulator, OPT does not do any flow balancing, but accepts the user input as is. The only thing that the simulation model takes care of is that if the out-flows at off-ramps exceed the flows entering into the system, those off-ramp flows are never achieved.
2. What does it mean - "never achieved"?
OPT allows specifying volumes exiting the system through off-ramps in two ways: 1) as portions of the freeway flow (split ratios); or 2) directly - as expected flows. In the first case, one can never direct more traffic to the off-ramp than there is in the corresponding freeway section. In the second case, it possible that the expected off-ramp flow exceeds the freeway traffic. In this case, the actual flows computed by the OPT model will be less the user's expected off-ramp flows.
3. How does OPT deal with the weaving that occurs when vehicles enter and exit managed lanes? Does an internal algorithm reduce capacity or must the user enter reduced capacity on the relevant link? If the former, what is the algorithm?
The OPT model has an internal algorithm that computes traffic exchange between the general purpose (GP) and managed lane groups. When traffic volumes are high, competition for a space in one or the other lane groups intensifies resulting in throughput reduction. There is a user-settable simulation parameter that can tune the amount of unforced lane changes. The logic behind the lane changes will be provided in the documentation.
4. Will OPT be able to analyze both HOV and HOT lanes? How will OPT deal with static and dynamic pricing for HOT lanes?
Yes. The user can set the schedule and specifics of the managed lane policies on all or selected road sections. Specifics include which vehicle types are granted a free access, which vehicle types are banned, and which vehicle types can be admitted after paying a toll and when.
5. Will OPT provide analytical capabilities for a) on-demand ramp metering; b) locally adaptive coordinated ramp metering; and c) corridor adaptive coordinated ramp metering?
Currently implemented are a) fixed rate time of day ramp metering - where a user can specify metering rates and turn metering on/off based on a schedule; and b) ALINEA - local adaptive ramp metering. Presently, there is no coordinated ramp metering scheme in OPT.
6. Will your documentation provide direction and examples about how to calibrate the model outputs against observed speeds and volumes?
The documentation will provide a general guideline for model calibration and a few specific examples. However, there will be no elaborate calibration handbook covering all corner cases.
7. What is the structure of the .opt configuration file and the internal data structure representing the simulation model and its output.
If you create a simple scenario (road network + demand + out-flows + controllers) in OPT and save this scenario in the .opt file, you can then open this .opt config file in any text editor. It is a human-readable XML file, and its structure is self-descriptive.