Dr. David Brownstone of the University of California, Irvine, presented modelled consumer responses to weight‑based fees using the DynaSim forecasting framework maintained by the California Energy Commission. Brownstone grouped light‑duty vehicles into 27 vehicle classes by size and fuel type and ran counterfactual simulations comparing a baseline (no new fee) to two stylized fee designs.

Key modeled scenarios and results

1) Onetime purchase surcharge (point of sale): Brownstone simulated a linear surcharge of $5 per pound on the portion of a vehicle’s weight exceeding 3,800 pounds (the approximate 2024 mean weight). Under that design the model projects, by 2040, a 2.5% decline in the 90th‑percentile vehicle weight, a 1.2% decline in the mean fleet weight, a 17% decline in the number of “large SUVs,” and a 10.5% decline in heavy and standard pickup trucks. The scenario produced an estimated annual revenue in the model of about $4.6 billion by 2040 (the figure accounts for modeled behavioral response). Brownstone cautioned that manufacturer responses (making new vehicles lighter) were not modeled, and such responses would probably reduce revenue while amplifying fleet‑weight declines.

2) Annual registration surcharge: The study tested a recurring fee of $0.10 per pound on the portion of vehicle weight above 3,800 pounds applied to registered vehicles. That annual charge produced much smaller projected fleet effects by 2040: mean weight down ~0.26%, large SUVs down ~4%, heavy/standard pickups down ~3%, and modeled annual revenue of roughly $1.45 billion by 2040. Brownstone explained purchase fees are more salient and certain to buyers at the point of sale and therefore produce stronger simulated shifts in purchase choices; annual fees are discounted or perceived as politically uncertain and thus have smaller modeled effects on purchase behavior.

Electric vehicles and exemptions

Brownstone’s simulations show that exempting electric vehicles (EVs), or EVs and plug‑in hybrids, from a purchase surcharge raises EV market share relative to a non‑exempted surcharge but substantially lowers projected revenue and removes most of the fleet‑weight reduction. For example, the baseline purchase‑surcharge scenario decreased EVs by 2.3% (2040) and plug‑in hybrids by 4.3%; exempting EVs reverses the EV decline but reduces revenue from about $4.6 billion to roughly $1.8 billion.

Model caveats and policy implications

Brownstone emphasized data limitations: vehicle weights are not publicly available for all make/model/year combinations and much of the detailed data used in DynaSim is proprietary or expensive. The model does not incorporate a full manufacturer response function (vehicle redesigns) and assumes used‑vehicle depreciation factors that were updated with purchased data. Brownstone noted fleet turnover is slow (only about 10% of vehicles are new in a given year), so any purchase‑driven policy will take many years to reach full effect. He and task force members discussed side effects: rising used‑vehicle prices, possible cross‑border registration shifts, equity implications for households and professions that rely on larger vehicles, and the tradeoff between safety and climate policy if EV exemptions are adopted.

Task force reaction

Members asked for more study of income and geographic distribution effects, potential exemptions for disability and professional needs, and the interplay between fees and investments in safe infrastructure. CTC staff said it will circulate a draft summary and asked members to submit written comments that can be incorporated into the commission’s findings.