Research Idea Details

Research Idea Scope

Emission factors versus speed curves generated using the MOVES3 model exhibit very anomalous behavior at higher road grades that are within the range encountered in project-level air quality analyses for NEPA and conformity. The effects are most pronounced for particulate matter (PM) and carbon monoxide (CO), particularly above road grades of about 5%, but are also observed for greenhouse gases (GHGs) and other pollutants. The anomalous behavior varies by vehicle type (heavy duty versus light duty), fuel type (gasoline versus diesel primarily) and road type (freeway versus arterial street.) Freeway ramps and arterial streets can have much higher road grades than freeway mainlines, so project-level air quality analyses conducted for state DOTs that include these facilities may involve modeling for higher road grades more frequently than may be generally recognized. In the absence of a study characterizing the extent of the issue with modeling higher road grades, state DOTs may unknowingly apply the model for projects involving higher road grades than could be defended from a technical basis or – worst-case – in litigation. The proposed study would systematically and rigorously document the anomalous behavior (including a sensitivity study) in emission factor/rate versus speed curves for a broad range of road grades that may be encountered in practice, seek to identify possible underlying cause(s) for any anomalous behavior, and make recommendations for resolving the identified issues.

Depending on funding availability, data may be obtained or  collected to better characterize drive cycles or operating mode distributions for higher road grades, as the use of default driving cycles developed for at-grade operations may be a significant contributor to the observed anomalous behavior. The high road grade drive cycle or opmode data would then be used in sensitivity testing to assess whether modeling results are improved. To limit costs, the use of readily-available drive cycle data for higher road grades  (e.g., as collected by the Texas transportation Institute, which however may be limited to select facility types) would be preferred over conducting field tests for new data. A literature search would be conducted to check for all available high road grade drive cycle data.

Urgency and Payoff

NEPA documents that rely upon MOVES modeling involving higher road grades may be inaccurate and subject to increased risk of litigation for PM, CO and GHGs. It is important to identify the underlying causes in order to begin the process to resolve them, and this proposed study would be the first step.