In April 2021 the TRPA Governing Board updated AQ14. The update replaced the 40 year old NOx based standard (AQ14), with a standard grounded in the Region’s transportation and land-use goals and the vision for a more walkable, bikeable, transit-oriented, sustainable Tahoe, laid out in the Regional Plan and Regional Transportation Plan. Additional detail can be found in the staff report.

Threshold standard (AQ14) was established in 1982, and set a goal of reducing in-basin nitrogen emissions by 10% from 1981 levels, and benchmarked its performance to total regional VMT. In 1981 increased algal growth because of elevated nutrient inputs (phosphorus and nitrogen) was thought to be the primary driver of Lake Tahoe's clarity loss. Since 1982 a number of developments have occurred that have functionally rendered the original intent of the nitrate reduction threshold standard (AQ14) moot. First, improvements in tailpipe emissions controls have reduced nitrogen emissions by more than 66%, far greater than the 10% objective of the adopted standard, functionally accomplishing the goal of the standard. Second, the Total Maximum Daily Load (TMDL) scientific research established that fine particles were the principal driver of clarity loss. Each of the last four threshold evaluations have recommended that the 1982 VMT nitrogen deposition threshold standard (AQ14) be reviewed and updated.

The Governing Board is considering an update to the standard, that would relaign the standard from one rooted in concerns over nitrogen emissions to a standard that estimates a goals for reducing reliance on the automobile, reducing GHG emissions, and promoting mobility. 


2023 Evaluation

The 2023 Threshold Indicator evaluation is not available yet. Check back soon for updates.
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Applicable Standard

AQ14: Reduce vehicle miles of travel in the Basin by 10 percent of the 1981 base year values.

Key Points

  • The goal of the standard, a 10% reduction of mobile source NOx emissions from 1981 levels was accomplished more than 25 years ago. Mobile source NOx emissions today are less than a third of what they were in 2000 and are forecast to continue to decline as a result of increasingly clean automobiles.

  • While the intent of the standard was reducing NOx emissions, and four consecutive threshold evaluations have suggested the NOx - VMT relationship should be revisited, the standard has typically been evaluated as it is written, through VMT. VMT in 2018 was estimated to be 1,393,994, 3.4% lower than it was 1981 (1,443,319). The 3.4% drop in VMT is short of the 10% reduction identified in the standard.

  • NOx emissions from mobile sources have rapidly declined over the last 20 years.

  • VMT in Tahoe has remained within a relatively narrow band since the standard was adopted in 1982. VMT has generally fluctuated with macro-economic conditions, but never increased or decreased more than 10% 1981 levels.

Delivering and Measuring Success