New Mineta Transportation Institute (MTI) research, “Consistent VMT Mapping and Modeling in California: How Can We Better Assess the VMT Impacts of State and Local Transportation Projects?,” uses both qualitative and quantitative data, to answer the question: “What are the advantages and limitations of existing VMT calculators to determine the climate impacts of transportation projects to help meet California’s climate goals?” 

The study divided the evaluation of VMT impacts into two main steps: 

1. Qualitative analysis of the advantages and limitations of the existing VMT mapping and modeling tool, which included expert interviews.

2. Quantitative analysis of VMT mapping and modeling tools.

MTI Study Findings

Findings indicate that the consistency, contextual relevance, complexity, data accuracy, and user-friendliness of the VMT tools vary significantly based on their design and methodology, and each tool presents a set of limitations and advantages, making it suitable for a specific use or context but not necessarily for another. 

Recommendations for the state include the following:

• Improve access to accurate, validated data for creating and inputting into VMT models and tools.

• Help create context-sensitive VMT tools capable of capturing local context and change over time.

• Strengthen dialogue between jurisdictions to share information and tools.

• Encourage using an integrated approach to VMT analysis — which often combines the use of different tools and datasets for various stages of decision-making and scenario planning.

“Potential for exploitation or loopholes exists in some of the VMT tools,” explain the study’s authors. “For example, the NCST Induced Travel Calculator might potentially produce misleading results due to its conservative estimates and fixed elasticity values. In contrast, VisionEval minimizes loopholes through its detailed and comprehensive scenario analysis, though its complexity could lead to misinterpretation of the findings. Users need to fully understand these tools so they can choose the best one for their specific needs.”

Identifying Best Tools

The research demonstrates that each VMT tool has its own strengths and weaknesses. 

By understanding the consistency, context of use, data usage, complexity, ease of use, and potential for misuse or misinterpretation of these tools, policymakers and planners can choose the best tool for their needs and ensure accurate VMT assessments to help California meet its climate goals.