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143 approval of the interim report and 1 month for NCFRP Objectives review and contractor revision of the final report. It is anti- This research aims to address the following objectives: cipated that the research will not require fieldwork, labo- ratory testing, or travel in addition to meetings with the Determine the best methods/models to capture the effects project panel. of local traffic and vehicle parameters on vehicle emissions for different types of application and Determine how to best capture local traffic activity and 5.2 Refining Road Project-Level local vehicle characteristics for use in different emission Emission Estimates models. Methodologies Background Description of Tasks Previous research has indicated the importance of accurately Task descriptions are intended to provide a framework for reflecting the effects of local parameters on vehicle emissions, conducting the research. The panel is seeking the insights especially at the project or corridor level. These parameters of proposers on how best to achieve the research objectives. can include road grade, road capacity, congestion, and vehicle Proposers are expected to describe research plans that can aerodynamic coefficients, among others. Although there have realistically be accomplished within the constraints of avail- been many advances in methodologies to capture such effects, able funds and contract time. Proposals must present the there still is no clear guidance on the best methods for different proposers' current thinking in sufficient detail to demonstrate types of applications. With the release of the final version of their understanding of the issues and the soundness of their MOVES, scheduled for the end of 2009, EPA is indicating that approach to meeting the research objective. MOVES will be the required model for SIP and conformity analyses. However, it is unclear how MOVES should be utilized for project-level analyses. Task 1: Conduct Kick-Off Call MOVES employs a "modal" emission rate approach as a prelude to finer-scale modeling. It relies primarily on sec- Conduct a conference call with the panel within 30 days after ond-by-second vehicle emissions data to develop emissions contract initiation to discuss the revised work plan developed in rates, and better represents the physical processes from ve- response to the panel review of the research plan in the agency's hicles, including the ability to model cold starts and ex- original proposal. tended idling, which is especially critical for heavy-duty trucks. Although the modal approach taken by MOVES Task 2: Review Effects of Local Parameters seems appropriate to capture some local impacts, other tools, on Vehicle Emissions such as the Comprehensive Modal Emissions Model, devel- oped by UC Riverside under an EPA contract, provide a more Conduct a brief literature review on the effects of local direct and transparent way to account for factors such as parameters on vehicle emissions, aiming at selecting a list of vehicle aerodynamics, pavement quality, and road grade. parameters that should be included in the research (i.e., those As a result, it is unclear as to whether it will the best tool for with the most substantial effects on vehicle emissions). At a all applications, or how local traffic and vehicle data will minimum, congestion, road grade, and vehicle aerodynamics need to be collected for use in MOVES or other applicable should be considered. Other parameters such as pavement emission models. quality could also be included. Although this research does not strictly apply to heavy-duty trucks, the evaluation of truck emissions would greatly benefit Task 3: Determine Accuracy Needs and Limitations from this research project. Despite the fact that some trucks can avoid congestion by traveling during off-peak times, Determine the accuracy requirements and limitations for congestion is expected to worsen over time. Thus, the trend emissions analyses that aim at capturing the effects of local is that trucks will become more affected by congested roadways parameters on vehicle emissions. in the future. Additionally, voluntary programs such as EPA's This research needs to be framed by accuracy requirements. SmartWay, have been advocating for the use of devices that On one end of the spectrum, accuracy requirements for air improve either aerodynamic coefficients or rolling resistance quality analyses and emission estimation need to be determined. coefficients, and these parameters need to be properly captured This will guide the selection of appropriate methods to quantify in emission calculations. the effects of local parameters on emissions. At the other end

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144 of the spectrum, the limitations of methods (data collection, conversions would yield accurate estimates of the effects of traffic modeling, emission modeling) need to be assessed. such parameters on vehicle emissions. In other words, the right balance between how accurate methods should be and how accurate methods can be needs to be achieved. Task 5: Provide Interim Report This task will also consider the different types of applications Provide an interim report to panel members summarizing that might require the evaluation of effects of local parameters the findings from Tasks 2, 3, and 4. Panel members would on vehicle emissions. For example, projects that add road review the report and provide supporting concurrence and/or capacity, improve traffic operations, or manage travel demand recommendations for additional data gathering as needed. could have impacts on road congestion, and consequently on vehicle emissions. It will be important to consider these dif- ferent applications when evaluating accuracy requirements Task 6: Improve Methods to Model Traffic Activity and limitations. Task 6 will improve the methods to model traffic activity to reflect congestion impacts on vehicle emissions more accurately. Task 4: Evaluate Current Methods This will be accomplished by (1) the development of new con- gestion metrics that can be used in emissions calculations and Conduct an evaluation of current methods to capture the (2) the development of new methods for traffic data collection effects of local parameters on emissions, including the tradeoffs to gather the right type of information for emissions calcula- between accuracy and data limitations. tions, including information on vehicle mix. Current methods to evaluate congestion effects can be The modeling of traffic activity needs to be conducted in such roughly divided into three types: (1) speed correction factors, a way that it fulfills the needs of emissions and air quality (2) customized driving cycles, and (3) vehicle-specific power. analyses that aim to incorporate the effects of congestion. Currently MOBILE6 and EMFAC estimate the effects of In such a context, traffic modeling relies on three elements: congestion on emissions by using speed correction factors congestion modeling, traffic data, and vehicle configuration. that differentiate emission factors by average speed. Previous Congestion has traditionally been represented in terms of research has indicated that this method might work reason- road level of service (LOS) or total vehicle delay, and there are ably well for uncongested freeways but it is ill-suited to assess concerns about the use of such metrics as inputs in emissions the congestion effects on arterials and local roads or on con- models. LOS is a discrete measure of traffic conditions, while gested freeways. The use of modal emission models such as the estimation of emissions depends on continuous variables. CMEM can provide a more accurate representation of the Although LOS can be represented by an "average" driving cycle, effects of congestion on emissions, but they rely on the devel- there are criticisms associated with representing a level of opment of customized driving cycles that depend on heavy service by a single driving cycle, given that an LOS represents data requirements, and might not be representative of driving a wide variety of traffic conditions. As a result, there is a need to conditions other than those for which they were originally develop new congestion metrics that can be used in emissions developed. Somewhere in between are methods such as those estimation. proposed by MOVES, where a binning approach could pro- Traffic data need to be collected in a way that enables the vide a more accurate representation of driving conditions by calculation of such new congestion metrics. The basic concepts assigning the share of time in each combination of speed range of traffic theory, which model traffic based on traffic flow, and vehicle-specific power. However, it is uncertain how local traffic density, and average speed, currently determine traffic input driving parameters will be used to feed into the binning data collection processes. New methods for traffic data collec- approach. New methodologies need to be developed and tested tion need to be developed and implemented to gather the right to bridge the gap between traffic data availability and emis- type of information for emissions estimation. For example, sion methodologies that provide an accurate representation new technologies (e.g., GPS, cell phones) can collect traffic data of congestion. in real time, and methods to aggregate traffic data could both Regarding other parameters such as road grade and vehicle protect drivers' privacy and provide the appropriate inputs aerodynamic coefficients, some models can consider them for emission models. explicitly (CMEM), while others (MOVES) might require The VMT share by vehicle type is a key input to emission additional steps to convert these parameters into modified models, but information on vehicle type is rarely collected vehicle-specific power estimates. This research should exam- on site. Instead, it typically relies on vehicle registration data, ine the feasibility and levels of effort and technical expertise which can be a poor proxy for local traffic mix, especially for required to make such conversions, and describe whether the heavy-duty trucks. With the requirements of emission models