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    <title>Research in Progress (RIP)</title>
    <link>https://rip.trb.org/</link>
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    <copyright>Copyright © 2026. National Academy of Sciences. All rights reserved.</copyright>
    <docs>http://blogs.law.harvard.edu/tech/rss</docs>
    <managingEditor>tris-trb@nas.edu (Bill McLeod)</managingEditor>
    <webMaster>tris-trb@nas.edu (Bill McLeod)</webMaster>
    <image>
      <title>Research in Progress (RIP)</title>
      <url>https://rip.trb.org/Images/PageHeader-wTitle-RIP.jpg</url>
      <link>https://rip.trb.org/</link>
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    <item>
      <title>MOVES5 Project-Level Sensitivity Analysis: Evaluating Changes in On-Road Operations and Fuel Consumption</title>
      <link>https://rip.trb.org/View/2720317</link>
      <description><![CDATA[In the U.S. Environmental Protection Agency (EPA)’s regulatory model (MOVES), fuel use rates are functions of on-road operating conditions (speed and acceleration conditions). The model uses operating mode (OpMode) distributions, defined by vehicle specific power (VSP) or scaled tractive power (STP), speed and acceleration, to represent the time fraction of engine load. MOVES converts driving cycles into OpMode distributions for project-level analysis (using MOVES default or interpolated driving cycles, customized cycles from user inputs, or OpMode distribution inputs). However, the relationships between average speed and fuel use rates are non-linear.  Hence, it is critical to understand how various input variables (e.g., source type, model year, ambient temperature, and relative humidity) impact the sensitivity of these rates against average speed. The release of MOVES5 includes updates to algorithms since MOVES2014 (including VSP and STP parameters) and introduces base rates that are expected to alter these sensitivity profiles compared to the previous version, MOVES4.0.1. The research team will perform a comprehensive sensitivity analysis of the speed-fuel use relationships using the high-performance computing capabilities of MOVES-Matrix 5.0 (which generates identical results to the MOVES model but runs 200 times faster). The team will investigate the impacts of input variables on these sensitivities and explicitly compare the results against MOVES4.0.1 to document how model updates may affect planning outputs. Fuel use analysis on freeway corridors also depends on the interaction between traffic volume and operating speeds.  Because project-level analyses often aggregate data over time (e.g., one hour) and space (e.g., lane-by-lane to corridor), there is a risk of losing modal model fidelity under variable congestion conditions and variable fleet compositions. The team will perform an uncertainty analysis associated with the temporal and spatial aggregation of on-road operations data (flows and speeds) within the MOVES 5.0 framework, comparing these findings to prior studies to assess how data resolution impacts the accuracy of estimation within the simulator.]]></description>
      <pubDate>Wed, 01 Jul 2026 16:28:36 GMT</pubDate>
      <guid>https://rip.trb.org/View/2720317</guid>
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    <item>
      <title>Comparative Assessment of AERMOD v24142 with MOVES 5.0: Source Type Performance and Dispersion Model Sensitivity</title>
      <link>https://rip.trb.org/View/2720326</link>
      <description><![CDATA[The U.S. Environmental Protection Agency (EPA) recently released AERMOD v24142, the latest iteration of its regulatory dispersion model, alongside their updated MOVES5.0 fuel consumption and exhaust rate model. In prior research conducted by this NCST team for FHWA (using MOVES 2014b and AERMOD v19191), significant discrepancies in predicted concentrations were identified across various source type configurations (specifically AREAPOLY, VOLUME, LINE, RLINE, and RLINEXT) under identical conditions. This previous study suggested that AERMOD effectively integrated three separate models, depending on the source type employed, with VOLUME sources notably underpredicting concentrations at low wind speeds compared to RLINE (impacted by the MEANDER settings). This project will re-assess the source type relationships using the updated modeling framework. The research team will utilize the MOVES-Matrix 5.0 and the Partnership for an Advanced Computing Environment (PACE) supercomputing clusters at Georgia Tech to process massive iterations of source-receptor pairs for the I-75/I-575 Northwest Corridor (NWC) case study. The primary objective is to assess if the algorithmic updates in AERMOD v24142 have harmonized the output differences between source types observed in previous versions. The project involves two primary thrusts: 1) A direct comparison of the new modeling results (MOVES5.0/AERMOD v24142) against the team’s prior baseline (MOVES 2014b/AERMOD v19191) to quantify how regulatory updates alter predicted concentration magnitudes and spatial patterns; and 2) a targeted sensitivity analysis using dense, 3-dimensional receptor grids. This condensed sensitivity task will validate vertical and horizontal dispersion profiles to ensure that specific source configurations (e.g., RLINEXT with noise barriers) properly reflect plume behavior near complex infrastructure.]]></description>
      <pubDate>Wed, 01 Jul 2026 16:22:08 GMT</pubDate>
      <guid>https://rip.trb.org/View/2720326</guid>
    </item>
    <item>
      <title>The Effects of Road Types and Construction Activities on Particulate Matter and Development of Best Practices for PM2.5 Reduction</title>
      <link>https://rip.trb.org/View/2604527</link>
      <description><![CDATA[The research team will evaluate the impact of roads (paved and unpaved roads, and unpaved shoulders) and construction on 2.5 microns (PM2.5) emissions and develop strategies for reduction. Objectives include quantifying PM2.5 emissions from roads and construction sites, identifying high-risk areas using thematic mapping, and designing cost-effective mitigation measures like dust suppression and optimized paving practices. The research team will create a user-friendly decision-support toolkit to help prioritize interventions and assess emission reduction strategies. The project outcomes will provide actionable solutions for air quality planning at both project and regional levels, enabling the Texas Department of Transportation (TxDOT) to meet environmental regulations, improve public health, and reduce PM2.5 impacts. The research team will collaborate with the TxDOT project 0-7256 "Monitoring and Speciation of Particulate Matter Under 2.5 Microns (PM2.5) Composition across Texas Counties" to enhance data collection and analysis, ensuring effective mitigation efforts.]]></description>
      <pubDate>Mon, 29 Sep 2025 16:24:57 GMT</pubDate>
      <guid>https://rip.trb.org/View/2604527</guid>
    </item>
    <item>
      <title>Monitoring and Speciation of Particulate Matter Under 2.5 Microns (PM2.5) Composition across Texas Counties</title>
      <link>https://rip.trb.org/View/2593191</link>
      <description><![CDATA[Texas needs a detailed understanding of statewide particulate matter under 2.5 microns (PM2.5) sources, as current regulatory monitoring lacks the granularity for source apportionment. Since speciated PM2.5 data is limited, the research team will collect and analyze samples from multiple regions nearing or exceeding the 9.0 µg/m3 threshold set by the Environmental Protection Agency (EPA). The research team will conduct source apportionment analysis and highlight the prominent sources of PM2.5 emissions by region. This will support future research and regulatory efforts, such as developing and implementation appropriate emission reduction strategies. The research team will collaborate with state and local governments, academia and other stakeholders, to acquire any existing data and ensure local regulations and best practices are met. The research team will collaborate with the Texas Department of Transportation (TxDOT) project 0-7257, "The Effects of Road Types and Construction Activities on Particulate Matter and Development of Best Practices for PM2.5 Reduction" by sharing data, resources, and coordinating efforts to enhance data collection and analysis.]]></description>
      <pubDate>Tue, 26 Aug 2025 12:42:34 GMT</pubDate>
      <guid>https://rip.trb.org/View/2593191</guid>
    </item>
    <item>
      <title>An Economical and Sustainable Dust Suppressant for Gravel Roads</title>
      <link>https://rip.trb.org/View/2508967</link>
      <description><![CDATA[The 66,000-mile-long network of unpaved gravel roads connect 1.2 million rural Iowa population and serves as a backbone to Iowa’s $27 billion per year agrarian economy. On unpaved roads, fugitive dust emanates from the mechanical interaction between the moving vehicles and the crushed aggregates. Fugitive dust primarily comprises of soil minerals (e.g., oxides of silicon, aluminum, calcium, and iron) with particulate material sizes lower than 10 μm (PM10) [4]. According to the National Transportation Statistics (NTS) report published in 2018, approximately 18.5 million short tons of PM10 and 5.34 million short tons of PM2.5 particulates (size lower than 2.5 μm) are entrained into the air annually. About 35% of this particulate material comes from unpaved roads. From the health, economic, and safety points of view, the generation of fugitive dust poses a serious threat to road users and people living in the vicinity of the unpaved roads. Furthermore, the unpaved roads will deteriorate faster due to the loss of fines that bind the larger aggregates. Fugitive dust lowers the visibility on gravel roads leading to accidents. Examples of some accidents occurred in the past due to fugitive dust include a chain of vehicle crashes near I-39 Wisconsin, accidents near Interstate 5 in Coalinga, California, a fatal ATV rollover crash in Carlton country, Minnesota, crashes in the intersection of Conejo Avenue and Highway 41, California; crashes on U.S. Highway 87 between Great Falls and Fort Benton, accidents in Butler County, Missouri, etc. Currently, chlorides especially Calcium Chloride are applied on gravel roads to lower the fugitive dust. Calcium chloride being a hygroscopic material absorbs moisture from the atmosphere that cements the fine particulate material. However, chlorides are detrimental to concrete, corrode automobiles, lower the fertility of soils, and contaminate water bodies. The objective of this project is to synthesize and characterize a low-cost and sustainable dust suppressant that has both hygroscopic nature and agglomeration capability. To this end, both wet and dry formulations will be synthesized. Evaporation tests and wind tunnel tests will be conducted followed by field tests. Preliminary studies suggest that the wet formulation is at least 6 times better than traditional chloride-based dust suppressants.  ]]></description>
      <pubDate>Wed, 12 Feb 2025 12:37:54 GMT</pubDate>
      <guid>https://rip.trb.org/View/2508967</guid>
    </item>
    <item>
      <title>Highway Construction Impact on Air Quality</title>
      <link>https://rip.trb.org/View/2417309</link>
      <description><![CDATA[This project will collect air quality measurements along I-270 in Denver as part of a roadway reconstruction research project. The project will help determine the levels of particulate matter and other pollutants in the air along I-270 before and during different phases of construction. The project will also inform the Colorado Department of Transportation (CDOT) of the utility of a range of measurement instruments and configurations allowing CDOT to select appropriate measurement strategies for future needs. With the data, mitigation efforts can be implemented to reduce pollution levels. The data will also allow the general public to be aware of these pollution levels and make more informed decisions on their potential exposure. Measurements will occur at approximately ten (10) primary locations along I-270 using a variety of technologies. Measurements will be real-time with data uploaded to the cloud and a public-facing website.]]></description>
      <pubDate>Wed, 14 Aug 2024 14:07:14 GMT</pubDate>
      <guid>https://rip.trb.org/View/2417309</guid>
    </item>
    <item>
      <title>Update ACRP Report 84: Guidebook for Preparing Airport Emissions Inventories for State Implementation Plans</title>
      <link>https://rip.trb.org/View/2413894</link>
      <description><![CDATA[The Environmental Protection Agency (EPA) regularly updates its National Ambient Air Quality Standards (NAAQS) for criteria pollutants, classifying areas that do not meet these standards as nonattainment areas. Such designations require states to develop State Implementation Plans (SIPs) that estimate future emissions and outline necessary control measures. The Clean Air Act (CAA) mandates that federally approved projects demonstrate conformity with the applicable SIP, known as General Conformity. Projects exceeding the minimums thresholds must undergo a General Conformity Determination, highlighting the need for accurate emissions inventories in SIPs.

Since the release of the Airport Cooperative Research Program (ACRP) Report 84: Guidebook for Preparing Airport Emissions Inventories for State Implementation Plans (2013), the EPA has lowered the NAAQS for ozone and PM2.5. This has resulted in an increased number of nonattainment areas, subjecting airport improvement projects to greater scrutiny. As airport operations are projected to grow, it is crucial that SIPs accurately account for the resulting emissions, particularly for projects like new runways and terminals.

Research is needed to update ACRP Report 84: Guidebook for Preparing Airport Emissions Inventories for State Implementation Plans and for airport operators,  inside and outside attainment areas, who are more frequently conducting inventories for reasons beyond SIP, such as voluntary commitments, environmental, social, and governance (ESG) reporting, and state and local initiatives.

OBJECTIVE: The objective of this research is to develop a guide for US airports on how to develop emissions inventories for purposes beyond federal actions, while building on and updating ACRP Report 84: Guidebook for Preparing Airport Emissions Inventories for State Implementation Plans.]]></description>
      <pubDate>Mon, 05 Aug 2024 17:57:57 GMT</pubDate>
      <guid>https://rip.trb.org/View/2413894</guid>
    </item>
    <item>
      <title>Impact of Freight Activity in and Around Ports</title>
      <link>https://rip.trb.org/View/2335159</link>
      <description><![CDATA[In many parts of the United States, air pollution from freight-related sources, such as heavy-duty diesel trucks, is prevalent in and around communities near freight hubs, such as ports, railyards, and warehouses, causing disproportionate burdens on the community members, especially children, seniors, and people with underlying medical conditions. The objective of this collaborative project is to assess the air quality impacts of goods movement in communities near freight hubs. As part of this project, the project team will conduct an evaluation of the freight movement near warehouses and distribution centers in Inland Southern California, measure air quality in the nearby communities, identify actionable solutions for mitigating the air quality impacts, and engage with the communities to translate the identified solutions into community actions.  ]]></description>
      <pubDate>Tue, 06 Feb 2024 16:53:49 GMT</pubDate>
      <guid>https://rip.trb.org/View/2335159</guid>
    </item>
    <item>
      <title>Evaluating Carbon Reduction in Project Selection and Planning</title>
      <link>https://rip.trb.org/View/2329694</link>
      <description><![CDATA[No abstract provided.]]></description>
      <pubDate>Wed, 31 Jan 2024 17:48:16 GMT</pubDate>
      <guid>https://rip.trb.org/View/2329694</guid>
    </item>
    <item>
      <title>Air Quality Inside Buses</title>
      <link>https://rip.trb.org/View/2149961</link>
      <description><![CDATA[The COVID-19 pandemic brought air quality to the forefront of the transit industry. In the summer of 2022, due to the immediate need to understand the issue, the Transit Cooperative Research Program (TCRP) conducted its first Insight Event. TCRP Insight Event--Air Quality in Transit Buses explored how air quality inside transit vehicles, especially buses, may contribute to the spread of infections. During that event, presentations and conversations about dispersion, ventilation, circulation, and filtration issues were held. Presentations from the event and the literature search results are available on the TCRP Insight Event web page at https://www.nationalacademies.org/event/06-21-2022/trb-tcrp-insight-event-air-quality-in-transit-buses. 

Since that event and the end of the pandemic’s restrictions, the public transit industry has learned that air quality inside transit buses matters to bus operators and passengers. There is an increased focus on reducing the concentration of pathogens containing respiratory aerosols and other harmful pollutants in the air inside a bus cabin. Transit agencies are working to increase operators and passenger confidence in air quality. With increased confidence, riders will return, and it will be easier to hire bus operators. 

Transit systems are analyzing the current air quality inside their buses to better understand current airflows and possible risks. Measuring and controlling air quality inside the bus cabin has proven difficult.  Buses idle, constantly open their doors to embark or disembark passengers, and are exposed to traffic-related air pollutants, such as  exhaust.  

This reality has not hampered the desire to improve air quality inside cabins. Transit agencies are employing the following solutions to mitigate poor air quality: dilution, which consists of bringing more fresh air inside the bus while sending indoor air out; filtration with the use of better-quality filters; and cleaning, including the use of ultraviolet light and photocatalytic oxidation.  

Research is needed to find clear solutions to improve air quality on buses for operators and passengers. Transit systems are doing the best that they can to protect their employees and passengers. However, research can provide information to improve air quality and standardization of practice. 

The objective of this research is to create a research document that helps transit agencies understand air circulation inside a typical 40-foot heavy-duty transit bus and finds solutions to protect employees and passengers without decreasing passenger comfort, safety, and reliability of the system. The research should help guide the development of future design and performance criteria to support better transit rolling stock procurement and heating, ventilation, and air conditioning (HVAC) operations in emergency conditions (e.g., airborne diseases and wildfires).]]></description>
      <pubDate>Mon, 10 Apr 2023 17:08:13 GMT</pubDate>
      <guid>https://rip.trb.org/View/2149961</guid>
    </item>
    <item>
      <title>Modeling and Analysis Tools</title>
      <link>https://rip.trb.org/View/1859214</link>
      <description><![CDATA[The purpose and need for this lAA is to support the administration
of FHWA's air quality and highway noise programs, compliance with current statutory and regulatory requirements, and the development of future legislature, regulatory and policy development for the following requirements:
(1) Transportation Conformity provisions of the Clean Air Act and its implementation regulations; 
(2) Highway noise levels and standards; 
(3) Congestion Mitigation and Air Quality Improvement (CMAQ) program; 
(4) Provide technical assistance to State Departments of Transportation (DOTs) and metropolitan planning organizations (MPOs) to ensure the timely delivery of highway projects to address requirements such as the South Coast Air Quality Management District v. the Environmental Protection Agency decision and the new nonattainment areas designated for the 2015 ozone standards. This technical assistance to State DOTs, MPOS, and other transportation stakeholders in conducting emissions modeling and analysis will make certain that these areas meet conformity requirements for their plans, programs, and projects.]]></description>
      <pubDate>Tue, 15 Jun 2021 16:34:05 GMT</pubDate>
      <guid>https://rip.trb.org/View/1859214</guid>
    </item>
    <item>
      <title>CMAQ Scenario Testing</title>
      <link>https://rip.trb.org/View/1662705</link>
      <description><![CDATA[The objective of this task order is to assess the potential of synergistic emissions benefits of grouped projects funded by the Congestion Mitigation and Air Quality (CMAQ) program. This research will help inform investment decisions by States and Metropolitan Planning Organizations (MPOs) by assessing the synergistic effects of grouping multiple CMAQ funded projects in producing emissions and congestion reductions. This research may also serve to inform the application of 23 USC 149(j) which allows for optional programmatic eligibility for CMAQ projects.
]]></description>
      <pubDate>Wed, 30 Oct 2019 12:01:51 GMT</pubDate>
      <guid>https://rip.trb.org/View/1662705</guid>
    </item>
    <item>
      <title>ASCENT Project 20 - Development of NAS Wide and Global Rapid Aviation Air Quality</title>
      <link>https://rip.trb.org/View/1502039</link>
      <description><![CDATA[No abstract provided.]]></description>
      <pubDate>Tue, 13 Feb 2018 11:38:36 GMT</pubDate>
      <guid>https://rip.trb.org/View/1502039</guid>
    </item>
    <item>
      <title>ASCENT Project 19 - Development of Aviation Air Quality Tools for Airport-Specific Impact Assessment</title>
      <link>https://rip.trb.org/View/1502038</link>
      <description><![CDATA[No abstract provided.]]></description>
      <pubDate>Tue, 13 Feb 2018 11:31:41 GMT</pubDate>
      <guid>https://rip.trb.org/View/1502038</guid>
    </item>
    <item>
      <title>Methods for State DOTs to Reduce Greenhouse Gas Emissions from the Transportation Sector</title>
      <link>https://rip.trb.org/View/1467498</link>
      <description><![CDATA[Many methods and tools are available to measure greenhouse gas (GHG) emissions and to evaluate expected GHG emissions reductions from transportation-related strategies. Despite the availability of methods, state DOTs face challenges to the integration of these methods into their planning and programming processes, including limited funding, incomplete data, lack of staff capacity, absence of strong incentives, and the addition of another layer of analysis to an already complex transportation decision-making process. These challenges make it difficult for state DOTs to develop and manage the transportation system in a way that will reduce GHG emissions, and to document changes in GHG emissions from the transportation sector. 
 
Selecting appropriate methods requires matching the needs and decision-making context of a state DOT with the characteristics of the method. Some state DOTs have adopted a method to evaluate GHG emissions reductions, yet struggle to link it with planning and programming decisions. State DOTs mandated to reduce GHG emissions from the transportation sector need a robust method to evaluate reductions that provides clear direction for selecting effective transportation strategies and defensible estimates of expected impacts on emissions while accounting for confounding factors and uncertainty. Other states may be interested in methods to calculate cost-effectiveness of transportation strategies in reducing GHG emissions.
 
Guidance on GHG emissions reduction strategies for state DOTs was developed under the second Strategic Highway Research Program (SHRP2) Capacity Project C09, titled Incorporating Greenhouse Gas Emissions into the Collaborative Decision-Making Process (https://www.trb.org/Main/Blurbs/166936.aspx). The practitioner guide and accompanying research report include information on GHG-reducing transportation strategies and a technical framework for assessing baseline GHG emissions and the effects of potential projects and strategies. The technical information was accompanied by a series of case studies of state DOT and metropolitan planning organization (MPO) efforts to assess GHG emissions in planning and project development. Although the SHRP2 project provided considerable detail on available methods, implementation of the framework has been limited. 
 
Since the SHRP2 effort, new methods and tools have been developed. Among these is FHWA’s Energy and Emissions Reduction Policy Analysis Tool (EERPAT), which evaluates the energy implications of a wide variety of policy options at the state or county level. Currently available methods vary considerably in their level of detail, data requirements, rigor, and applicability to state DOT planning and programming decisions. Selecting a method to evaluate GHG emissions reductions requires understanding the appropriateness of the method for the decision-making context, identifying opportunities to integrate GHG considerations into the decision-making process, as well as gaining leadership support and building organizational capacity to apply the method. Technical issues including data availability must also be resolved.
 
The objective of this project was to provide guidance on currently available, practical, and innovative methods for state DOTs to assess and advance transportation-related GHG reduction strategies in planning and programming. The guidance will support state DOTs’ efforts to integrate GHG emissions considerations into their decision-making processes as well as methods appropriate for collaborative activities undertaken with partners to shape outcomes outside the purview of a state DOT. The guidance should be relevant for the evolving role of state DOTs and be adaptable to a changing regulatory environment at the state and federal levels, while also considering uncertainties related to future travel behavior, the future vehicle fleet, and other demographic and technological changes.
 
The project also sought to broaden the practice of addressing GHG emissions in state DOT decision making through targeted implementation activities to support state DOT adoption or updating of GHG emissions reduction methods.]]></description>
      <pubDate>Fri, 19 May 2017 08:49:25 GMT</pubDate>
      <guid>https://rip.trb.org/View/1467498</guid>
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