Office of Planning, Environment, & Realty (HEP)
The afternoon discussion with the panel members in the operations group was used to address questions listed in Section 4.0 of this report. The moderators intended on discussing three major topics: Process and Policy, Microsimulation, and Dynamic Traffic Assignment. Due to time constraints, however, the moderators could not specifically address the questions related to microsimulation and DTA. There was some discussion, however, on microsimulation and DTA within the framework of the overall discussion on Process and Policy.
Major discussion themes and key issues discussed by the moderators, panel members and participants are described below.
The group identified the need for earlier scheduling, collection, and warehousing of survey data. This includes O/D Surveys, SPS, and Revealed Preference Surveys (RPS). It was noted that data collection should be conducted around six to nine months prior to the initiation of the PD&E Study.
O/D surveys may be categorized as either "behavioral" or "non-behavioral." Behavioral O/D data are preferred to non-behavioral O/D data, because they provide more robust insights on trip and traveler characteristics (such as trip purpose, trip frequency, and income). Non-behavioral O/D examples are GPS route-based data, cell phone probe data, or Bluetooth reader data. Behavioral O/D data are found to be valid for many years, while non-behavioral O/D data are valid contingent to changes to the roadway network. Non-behavioral O/D data generally have a shelf life of five to ten years. A new SPS is generally required for investment-grade T&R studies to satisfy bond holders.
Some panel members stated that it is better to conduct travel surveys more frequently with smaller sample sizes than larger, less frequent surveys. Panel members stated that there are numerous SPSs available and the data from them can be adjusted to reflect socioeconomic conditions of different areas. The Florida's Turnpike Enterprise (FTE) has a repository of SPS data. It was recommended the FDOT Central Office create one using the data from FTE as a starting point. All SPS data and instruments should be made available for future express lane projects.
Questions were raised regarding MOEs that justify an express lanes project. The justification depends of the purpose and need of the project. The purpose and need should be communicated early in the project life-cycle. It should be clarified whether congestion relief or revenue generation is the primary goal. If congestion relief is a primary goal, the project should have a clear operational benefit in travel time savings, which could be improved corridor reliability, speed, or vehicle throughput. If the project's purpose and need identify reliability at the primary MOE for project evaluation, FHWA would prefer to be presented with results indicating facility or wider network reliability, not only express lane reliability. PET, discussed in Section 5.0, offers many similar MOEs.
Finance criteria should include revenue and toll rates. If revenue generation is the primary goal, the project should provide the ability to fund O&M costs at a minimum. If possible, the project may be able to fund a portion of the capital construction cost or provide new funding for public transit on the corridor. In terms of revenue generation, the availability of the excess demand to use the express lanes should also be considered.
The panel members referenced NCHRP 722 Decision-Making Framework for Assessing Highway Tolling and Pricing as resource that can assist project selection and MOE determination. It was also recommended that goals of the project should be specific, such as to reduce delay at Ramps A, B, C and D from 360 seconds to under 120 seconds. Another example is to reduce the queues at Lake, Randolph and Monroe Streets from over 300 feet to less than 125 feet on northbound and southbound approaches.
The group was asked to discuss when an operational analysis should be conducted for evaluating the express lane ingress/egress points. Many agreed that the analysis should be identified in the early planning stages and that a vehicle O/D trip table is critical for the assessment. The panel members recommended using a route choice mesoscopic DTA model to assess ingress and egress traffic. One audience member stated that a DTA model has been developed for the I-95 Corridor in Palm Beach County, and it could be used to evaluate access points.
From an operations perspective, the access points should add value to the users and not create traffic congestion at merges/diverges areas or express lane terminal locations. The identification of access points should consider origin-destination patterns, average trip length, access to park-n-ride lots, and access to major destinations. Locations of the ingress and egress points should be consistent with user experience. Depending on demand variations, O/D patterns, and overall capacity utilization, more access points may not necessarily provide better congestion management. In dense urban areas without a by-pass around the core urban region, an express lane with limited-access could be a very effective congestion management tool.
The panel members were asked about the demand model inputs for operational analysis in a microsimulation model. A travel demand model is necessary for operational analysis while there are then multiple methods/resolutions for traffic assignment (i.e., macro, meso, and micro). The issue becomes which robust lane choice model should to be used to estimate the demand.
One panel member stated that the VISSIM lane choice model is reactive (to en route information), as compared to the mesoscopic DTA demand model, which is based on a longer-term (less instantaneous) driver learning process. The panel agreed that demand inputs depend on the robustness of the model for the region. The priority ordering of model setups, as recommended by the panel, proceeds as follows:
Subsequent to the working session, one software vendor recommended that low-cost, dynamic microsimulation be the primary approach for examining the desirability of express lanes both in a planning mode and also in a more refined manner for operations analysis. As a second choice, a static time and cost assignment methodology cited in NCHRP 722 could be used. The third choice could be a standard, multi-class assignment with an appropriate distribution of value-of-time.
A discussion was held on which pricing policy should be used for operational analysis: revenue maximization or traffic optimization/maximization. The traditional approach is to evaluate operations under a traffic maximization strategy where the express lane demand is capped at a maximum service volume of 1,650 vehicles per hour (vph) per lane. Under a revenue maximization approach, volumes will not reach this level. Each approach has different impact on mainline operations, weaving operations, and safety. The approach will also play a role in determining access points.
The recommendation from the panel members is to run the microsimulation model with both extremes (maximum revenue and maximum traffic). FDOT District Two has performed a microsimulation analysis that considers the extremes for the I-295 express lane analysis. Express lane volumes were modeled at 1,650 vph and 825 vph. The T&R consultant should be able to provide the appropriate express lane volume under a revenue maximization approach. If the T&R study performs a revenue maximization scenario, FHWA may request to see the results in the Interchange System Access Request.
The panel members were asked about the preparation of a ConOps and how it integrates with the project development process. The ConOps can dictate pricing and operational strategies that would affect the operational analysis. At each level in the project development process, recommendations were made as to what would need to be included in the ConOps document.
At the planning-level, no robust or high-level details are required. General project statements include regional express lane context, operating policies, pricing policy, incident management, business rules, exempt vehicles, multimodal/BRT, and short distance versus long distance trips.
At the PD&E level, the ConOps will include all of the details from the planning level. In addition, the ConOps should include coordinating elements with traffic operations and Intelligent Transportation Systems (ITS) for integration of the express lane operations and toll collection systems.
At the Design-level, the ConOps should include all details from the PD&E level. In addition, the document should include coordinating elements with Systems Engineering for ITS supporting structure. The document should address incident management and work zone procedures. It may be necessary to perform microsimulation under these event-related traffic conditions. There should be detailed clarification on the pricing structure including the tolling algorithm that sets the price in the express lanes. Also, en-route travel time information through dynamic message signs shall be evaluated since this information impacts to operations and revenues.
The panel was asked whether they would recommend that FDOT establish a life-cycle demand model and microsimulation model philosophy. An example would be a microsimulation model that was created in the PD&E phase and enhanced for use in the Design phase. The FHWA Traffic Analysis Toolbox does consider life-cycle modeling a good management practice. The panel agreed that life-cycle modeling is good practice where appropriate. However, the agency should also consider the need for consistency, model development costs, data demands, increasing accuracy and time spans for express lane projects. It was noted that each FDOT District functions differently, so no single template can easily be applied to all Districts in terms of warehousing the models. No single position or department can be designated, so this issue should be discussed and decided at the District-level.