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Open research questions in Vehicle emissions and performance

26 unresolved questions extracted from the limitations and future-work sections of 466 Vehicle emissions and performance papers in our library. Each links back to the study that raised it.

What the literature leaves open

  • In recommendations are proposed: findings of line with this study, the following i. Government should strengthen the enforcement of regular vehicular emission through monitoring and stricter compliance measures. regulations ii. Functional vehicle emission testing centres should be into periodic vehicle established and inspection programmes across major cities. integrated iii. Policies should be introduced to gradually phase out old and high emission vehicles while promoting the adoption of cleaner and energy efficient alternatives. iv. Investment in safe, affordable, and reliable public reduce should be increased to transportation dependence on private vehicles. REFERENCES Ajayi, O. O., Afolabi, A. O., & Adewale, T. M. (2023). The impact of traffic mobility measures on vehicle emissions for heterogeneous traffic in Lagos City. Scientific African, 21, e01822. https://doi.org/10.1016/j.sciaf.2023.e01822 Adediran, S. A., Ojo, O. T., & Okafor, T. T. (2025). On road vehicular traffic emissions inventory and air quality on major roadways in Lagos City. African Transport Studies, 3, 100034. https://doi.org/10.1016/j.ats.2025.100034 Ayeni, T. S., & Iyeke, S. (2024). Evaluation of capacity and level of service for urban arterial road under mixed traffic conditions: A case study of Oba Adesida Road, Akure, Nigeria. Journal of Civil Engineering Science and Technology. https://publisher.unimas.my/ojs/index.php/JCEST/article/vie w/6412 International Energy Agency. (2024). Global EV outlook IEA. 2024: Moving https://www.iea.org/reports/global-ev-outlook-2024 increased affordability. towards IQAir. (2024). World air quality report 2023. IQAir. https://www.iqair.com/world-air-quality-report Krejcie, R. V., & Morgan, D. W. (1970). Determining sample size for research activities. Educational and Psychological FUDMA Journal of Sciences (FJS) Vol. 10 No. 11, June, 2026, pp 377 – 387 386 Assessment of Urban Traffic Characteristics… Maikano et al., FJS Measurement, https://doi.org/10.1177/001316447003000308 30(3), 607–610. United Nations Environment Programme. (2025). Global environment outlook 7. United Nations Environment Programme. Onyeka, O. O., Ifeyinwa, O. C., Ernest, E., Adunola, I. B., & Onyinye, N. J. (2020). Out door air pollution levels in vehicular traffic junctions in Nsukka and Enugu Metropolis, Nigeria. Open Journal of Air Pollution, 9(4), 105–115. https://doi.org/10.4236/ojap.2020.94008 Subair, S. O., Ibitoye, B. A., & Kuranga, A. T. (2024). Evaluation of traffic congestion in urban roads: A review. ABUAD Journal of Engineering and Applied Sciences, 2(2), 1–7.

    Assessment of Urban Traffic Characteristics, Vehicular Composition, and Stakeholder Perspectives on Emission Control in Major Cities of Nigeria · 2026 · DOI

  • This study provides high-resolution empirical evidence that localized roadway surface obstacles are associated with changes in vehicular emissions under real-world urban driving conditions. By integrating second-by-second PEMS measurements with YOLObased image detection, the analysis showed that obstacle-dense road sections presented higher CO2, CO, and NOx emissions than better-maintained sections. In the full dataset, the highest emission factors reached 478.2 g/km for CO2, 491.96 mg/km for CO, and 100.266 mg/km for NOx. Importantly, after filtering out major observable confounders—including curves, intersection buffers, and visible pedestrian or heavy-traffic interference—the obstacle– emission association remained observable, with obstacle-present observations showing average increases of 26% for CO2, 31% for NOx, and 42% for CO relative to obstacle-free observations. From a policy perspective, the findings indicate that roadway maintenance may generate environmental co-benefits beyond ride quality, safety, and asset preservation. In urban corridors where localized obstacles are frequent, maintenance actions may reduce operational disturbances associated with higher pollutant release and may therefore contribute to integrated transport, air-quality, and climate-mitigation strategies. However, the results should not be interpreted as definitive emission factors for pavement rehabilitation interventions. Rather, they provide evidence that roadway surface conditions are relevant enough to be considered in urban emission assessment, especially when combined with traffic, fleet, and operational variables. Several limitations should be considered when interpreting these results. First, the study was based on five urban corridors in one tropical city, which limits spatial generalization.

    Influence of localized roadway surface obstacles on vehicular emissions under real-world urban driving conditions · 2026 · DOI

  • through four complementary directions. First, the spatial and temporal coverage of field campaigns should be expanded to include more corridors, road classes, traffic regimes, seasonal conditions, and land-use contexts. This would improve statistical representativeness and clarify whether the observed obstacle– emission association is transferable across different urban environments. Second, broader vehicle and driver samples should including passenger cars, motorcycles, buses, be incorporated, and freight vehicles, because suspension response, vehicle mass, fuel type, and driving style may mediate how surface obstacles affect emissions. Third, future studies should integrate richer vehicle-dynamics variables, such as engine load, torque, road grade, acceleration, vertical vibration, and real-time vehicle specific power (VSP), enabling multivariable regression, structural equation modeling, or machine-learning approaches to separate roadway effects from traffic and behavioral effects more explicitly (Muhammad et al., characterization should be improved by distinguishing type, severity, geometry, spatial concentration, and recurrence, while distance-based image acquisition and before–after monitoring of maintenance interventions should be used to estimate potential emission reductions associated with roadway surface improvements. Together, these advances would strengthen the robustness, transferability, and policy relevance of the proposed framework. 2024).

    Influence of localized roadway surface obstacles on vehicular emissions under real-world urban driving conditions · 2026 · DOI

  • 3 t/a, though its realization faces transaction cost barriers including the lack of standardized transfer mechanisms and formal VOC trading infrastructure.

    VOC Emission Idle Rates and Differentiated Control Strategies for Chemical Enterprises Under China’s Discharge Permit System: Evidence from Jiangsu Province · 2026 · DOI

  • Vehicle emission inventories are highly sensitive to vehicle activity data, yet annual vehicle kilometers traveled (VKT) is still commonly represented using generalized default values whose representativeness at the city scale remains uncertain.

    Representativeness of Generalized Vehicle Activity Assumptions in Urban Emission Inventories and Policy Evaluation: Evidence from Haikou, China · 2026 · DOI

  • Based on the results of the bibliometric analysis, which demonstrate the dominance of topics related to Multi-Objective Optimization and carbon emissions alongside the limited application of hierarchical optimization methods in the context of developing countries, the primary agenda for future research is the development of a GPS-based eco-friendly path optimization model. This proposed framework is designed to directly address the gap identified in the literature, specifically the limited integration of dynamic optimization and emission analysis in green path models. By prioritizing carbon emission minimization through a strict lexicographic structure, the upcoming research aims to ensure that environmental sustainability is not merely an optional variable but the governing constraint of the optimization process. This approach is specifically tailored to address the unique challenges of developing countries, where traffic unpredictability often renders static models ineffective. To ensure the proposed framework is systematic and reproducible, the research stages are organized linearly from data acquisition to model validation. The process begins with the extraction of real-time traffic parameters via Google Maps API, which are then converted into a weighted graph representation. Subsequently, the optimization engine applies the Binary Integer Programming (BIP) formulation to solve the multi-objective problem hierarchically. This structured workflow allows for a clear translation of theoretical mathematical models into executable Python computations. Crucially, the framework includes a validation phase, where a sensitivity analysis using a 5% emission reduction threshold serves as a decision gate. This benchmark is established to distinguish meaningful environmental benefits from stochastic traffic variations and GPS data noise, which are particularly high in heterogeneous traffic environments like Indonesia. By setting this minimum viability margin, the model ensures that the recommended green routes offer genuine savings beyond the margin of error, balancing sustainability with operational efficiency.

    Systematic Literature Review of GPS-based Multi-Objective Environmentally Friendly Shortest Path with a Proposed Lexicographic Framework · 2026 · DOI

  • The tests discussed in the article are introductory in the area of RDE tests and provide an introduction into further studies of exhaust emissions and energy consumption in real driving conditions in conventional vehicles and vehicles with alternative engines, e.

    Determining the route for the purpose light vehicles testing in Real Driving Emissions (RDE) test · 2019 · DOI

  • China’s pollutant discharge permit system mandates total-quantity emission control for industrial volatile organic compounds (VOCs), yet the actual utilization of permitted capacity remains poorly studied.

    VOC Emission Idle Rates and Differentiated Control Strategies for Chemical Enterprises Under China’s Discharge Permit System: Evidence from Jiangsu Province · 2026 · DOI

  • The carbon emission constraint optimization framework has universality and can be extended to other traffic management scenarios such as ramp control, dynamic lane management, and regional traffic guidance.

    A Deep Reinforcement Learning Signal Control Algorithm for Traffic Carbon Emission Optimization · 2026 · DOI

  • Before actual deployment, it is necessary to build a full-chain trusted mechanism from training to deployment combining edge computing, data fusion, and security verification technologies.

    A Deep Reinforcement Learning Signal Control Algorithm for Traffic Carbon Emission Optimization · 2026 · DOI

  • Real-world signal control involves multi-department coordination and strict verification processes, imposing higher requirements on algorithm interpretability and reliability.

    A Deep Reinforcement Learning Signal Control Algorithm for Traffic Carbon Emission Optimization · 2026 · DOI

  • Actual deployment faces uncertainties in real-world traffic systems, sensor noise, and communication delays that may cause state estimation bias and affect policy effectiveness.

    A Deep Reinforcement Learning Signal Control Algorithm for Traffic Carbon Emission Optimization · 2026 · DOI

  • The state representation mainly relies on traditional traffic parameters and has not fully utilized lane-level and individual-level refined data available in the Internet of Vehicles environment, such as vehicle trajectories and signal phase timing.

    A Deep Reinforcement Learning Signal Control Algorithm for Traffic Carbon Emission Optimization · 2026 · DOI

  • The instantaneous emission model based on speed and acceleration does not account for differences in vehicle type, fuel type, and engine thermal state on emissions, limiting accuracy of emission estimation.

    A Deep Reinforcement Learning Signal Control Algorithm for Traffic Carbon Emission Optimization · 2026 · DOI

  • The determined toxicity indicators allowed to indicate their usefulness, to make comparisons between tested vehicles, and to identify directions for further work on the application and interpretation of these indicators.

    Determining the environmental indicators for vehicles of different categories in relation to CO2 emission based on road tests · 2017 · DOI

  • Since the current practice of estimation of vehicular emissions by aggregate emission factors does not account for the improved speeds resulting from capacity improvements, speed-dependent emission functions for various transport modes and pollutants are used in this study.

    Multiobjective Network Design for Emission and Travel-Time Trade-off for a Sustainable Large Urban Transportation Network · 2011 · DOI

  • However, a massive increase in the number of cars on the road have meant that pollution due to a number of gases and particulate species remains to be a problem.

    On Board Exhaust Emission Monitoring of Road Vehicles - A High Tech Solution to Pollution from Traffic? · 2008 · DOI

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26 open questions have been extracted from the limitations and future-work passages of 466 Vehicle emissions and performance papers in our library. Each one below links back to the study that raised it, so you can read the original claim in context.

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