Forest Trail


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Ultra Low Emissions Vehicle (ULEV)

A vehicle that meets the ARB's ultra-low emission standards of 0.125 grams per mile of NMOG + NOx. The average 2010 car sold in California is a ULEV. See our Drive Clean website.

Underground Storage Tank (UST)

Refers to tanks used to store gasoline underground. For more information, visIt the underground storage tank website.

Unit Risk Number

The number of potential excess cancer cases from a lifetime exposure to one microgram per cubic meter (µ/m3) of a given substance. For example, a unit risk value of 5.5x10-6 would indicate an estimated 5.5 cancer cases per million people exposed to an average concentration of 1 µ/m3 of a specific carcinogen for 70 years.

United States Environmental Protection Agency (U.S. EPA)

The federal agency charged with setting policy and guidelines and carrying out legal mandates for the protection of national interests in environmental resources. For more information, visit the U.S. EPA website.

Upstream Emissions

Emissions from processes that take place up to when the fuel enters a vehicle---typically during extraction, production, distribution and dispensing of the fuel.

Urban Airshed Model

A three-dimensional photochemical grid model designed to calculate the concentrations of both inert and chemically reactive pollutants in the atmosphere. It simulates the physical and chemical processes that affect pollution concentrations.

Used Vehicle

Any vehicle that has been transferred after being issued a title and has over 7,500 miles. (Reference statute: H&S code 43150-43156.)