VMT is an integral component, and its impact on both short-term and long-term projects must be analyzed. In short, short-term impacts get evaluated at a detailed project level concerning the vehicle miles travel analysis. Cumulative or long-term impacts get demonstrated through the consistency check with SCAG RTP/SCS.
Now, what are RTP or SCS? Simply put, it’s the regional plan demonstrating compliance with the conformity needs of the air quality & GHG reduction targets. In general, land use plans and projects consistent with the plans concerning project density, development, intensity, and location are a critical part of the regional solution. That helps in meeting the air pollution & GHG reduction objectives.
Land use and project plans deemed to be constant will have a less cumulative impact on the VMT.
Locational developments where RTP or SCS does not give an indication of development might indicate an impact on transportation.
But for projects and land use plans that don’t demonstrate the project impact, a less significant project impact conclusion will be sufficient that determines there’s no cumulative impact. It might be done by applying efficiency-based impact thresholds that include the following:
- VMT per capita
- VMT per employee or
- VMT per service population in impact analysis
Projects & land use plans under the efficiency-based impact thresholds will align with long-term VMT & GHG reduction objectives considering SCAG’s RTP/SCS. These plans that demonstrate the project impact via VMT thresholds or net increase thresholds for retail are to be inconsistent. It might have an impact on the VMT figure.
More evaluation might be necessary for determining whether the land use plan or project’s impact on VMT is noteworthy.
The analysis might get conducted by SCAG RTP/SCS Travel Demand Forecasting. That may happen with the cumulative “no project” scenario that represents adopted RTP/SCS horizon year conditions & cumulative “plus project” representing the population’s reallocation and employment growth on land supply changes with the proposed project.
Citywide VMT, work VMT per employee, VMT per service population, and household VMT per capita, depending on the type of project, may get calculated for scenarios. Any increase in the following above, which get forecast in adopted RTP/SCS, may constitute an impact due to the GHG reduction findings or regional air quality conformity:
- Household VMT Per Capita
- Work VMT Per Employee
- VMT Per Service Population
Additional Steps to Consider
When evaluating VMT impacts of entertainment projects, event centers, and or regional-serving retail, the overall cumulative analysis may include certain steps to compare the cumulative “plus project” scenario with the cumulative “no project” scenario that represents the adopted RTP or SCS cumulative year conditions. That may involve these steps:
- #1 Converting the Land Development Uses
Converting project land uses into appropriate employment categories used in RTP or SCS horizon year model. The applicant needs to adjust socio-economic parameters in TAZ to reflect the removals of the land uses.
- #2 Running the SCAG RTP/SCS four-step model
Running the model process for model cumulative “no project” for four time periods in that model for base cumulative “no project” scenarios & for cumulative “plus project” scenarios.
- #3 Calculating VMZT on Model Networks
It is imperative to calculate the VMT on the model network each time. Sum the amount and determine the daily VMT for every scenario. And then, you need to subtract the VMT for base cumulative “no project” scenarios from VMT for cumulative “plus project” scenarios. That will help you determine the overall change in the VMT daily.
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