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NCST Calculator Truck Adjustment

Method for adjusting NCST Calculator results to account for heavy-duty trucks

CEQA Guidelines section 15064.3 establishes vehicle miles traveled (VMT) as the most appropriate measure of transportation impacts. As a result, estimating induced travel attributed to transportation projects is a key component in evaluating VMT impacts. However, OPR guidelines exclude truck traffic from consideration in calculating induced travel. Section 15064.3, subdivision (a) of the CEQA Guidelines, states, “For the purposes of this section, ‘vehicle miles traveled’ refers to the amount and distance of automobile travel attributable to a project.” OPR further clarified in their 2018 Technical Advisory that “automobile” refers to on-road passenger vehicles, particularly cars and light trucks. Heavy-duty truck VMT could be included for modeling convenience and ease of calculation.

These circumstances have led to updated considerations when it is determined that the NCST California Induced Travel Calculator (NCST Calculator) is the appropriate tool for estimating induced travel. Specifically, the NCST Calculator does not exclude heavy-duty trucks from its elasticity estimates. Therefore, it is reasonable to allow for an adjustment to the results used in VMT analyses for transportation projects.

Upon consideration of the research associated with the NCST Calculator and input received by multiple stakeholders, both internal and external to the Department, VMT analyses related to transportation projects can use the following procedures:

  • Reduce the NCST-generated elasticity values for Interstate Freeways (Class 1 facilities) by 0.29 (from 1.0 to 0.71).
  • Reduce other highway (Class II and III) NCST-generated elasticities proportionately by 0.22 (from 0.75 to 0.53).

The source of these reduction values is one of the foundational papers used in calibrating the NCST Calculator; Duranton & Turner (2011) “The Fundamental Law of Road Congestion: Evidence from US Cities,” pp. 2638-9.

It is important to note that the above-described procedure applies only to using the NCST Calculator to predict induced travel. If VMT results from a Transportation Demand Model (TDM) are used for comparison to NCST Calculator results, the trucks should be removed from the estimates of induced travel and the procedure to exclude heavy trucks from the results would have to be documented specifically for the TDM that is used.