Key challenges in California’ greenhouse gas reduction target setting process under SB 375 (2008) surfaced during the Regional Targets Advisory Committee (RTAC) lifespan. SB 375 requires the California Air Resources Board (ARB) to set regional targets for the purpose of reducing GHG emissions from passenger vehicles, for 2020 and 2035 for each of the 18 MPOs.

The California Air Resources Board played the role of conductor, orchestrating a symphony of unharmonized MPO models, data benchmarks, geographic diversity, and political support for this process.  The RTAC process in coordination with ARB created an MPO-driven GHG reduction target setting process utilizing existing regional scenario planning efforts. The nine-month evaluation process of best methods to assign GHG emission reduction targets included four central questions, which framed many technical challenges:

  • Should targets be for GHG or VMT?
  • Is an Absolute or Relative target better?
  • Do we measure per capita or per household metrics?
  • What baseline is more realistic: 2005 or 2020?


Despite SB 375’s language requirements to assign GHG reduction targets specifically, the RTAC still struggled initially in determining the use of a metric – namely GHG emissions versus vehicle-miles-traveled (VMT).  In addition to the statue not giving ARB direction to establish VMT targets (explicitly directing GHG targets), there was concern that a VMT metric would not fully capture GHG effects due to local actions for system efficiency and vehicle fleet/fuel programs which go beyond ARB’s statewide requirements.

Absolute vs Relative

While the AB 32 Scoping Plan held a temporary placeholder of an absolute GHG reduction of 5 MMTCO2E[1], a relative “percent reduction from base year” was ultimately chosen during the RTAC process because a percent reduction from a base year is a more practical method for local governments to understand and relate to what the region needs to achieve – despite the fact that they would achieve the same reduction result.

Measurement Metrics

After several RTAC meetings, a per capita GHG reduction methodology was recommended to ARB – resulting in overall acceptance when the final target percent reductions were allocated to the MPOs.  The League of California Cities describes a per capita metric as being “fair, easily understood, and supported with current data.”  After much discussion around how to meet affordable housing targets also set in SB 375, the RTAC process resulted in a per capita metric as a means to not penalize growing regions.  Likewise, there was stakeholder concern over encouraging regions to stop growing if a per capita metric was not used, driving housing prices up.  With a per capita GHG metric, the expectation was around individual ability to reduce emissions by a given percentage.

Benchmarking: Baseline vs Trend

The challenge area which received the greatest level of attention during the RTAC process was the insensitivity and inconsistency in travel demand models across the MPOs to measure GHG emission reduction from various land use and transportation strategies.  As a result of these concerns, the need for modeling updates and the development of tools which could be used transparently to engage local governments took the spotlight.  Limited faith in modeling capabilities was a strong motivator for not using a trend projection to benchmark targets.  Because of the difficulty in projecting trend conditions, particularly related to the current economic downturn, ARB chose a base year of 2005 to apply the MPO per capita GHG percentage reductions.

Other Issues

Other challenge issues included MPO allocation for interregional travel and regional jobs/housing needs, as well as demographic forecasting limitations and variations in benchmarking data to establish a base year for target reduction.  The Strategic Growth Council announced $12 million from Proposition 84 funding would go to modeling updates across California’s MPOs, and other state agencies such as ARB and Caltrans are investing in regional data improvements.  However, for the purposes of setting initial targets ARB relied heavily on existing data from each of the MPOs who then proposed targets which were compared to research from the University of California at Davis for various land use and transportation strategies.

Target Recommendations

California saw overall success in the target setting phase with a unanimous vote by the ARB Board to adopt the staff-recommended targets for the State’s four largest MPOs — 13-16% by 2035, and 10% for the Valley. The targets for the Valley act as a placeholder to be revisited in 2012 when better data and tools in the Valley are expected.  The State, MPOs and major stakeholders felt that the process yield “ambitious and achievable” per capita GHG reduction targets.

The following recommendations for target setting provided by the RTAC to ARB were addressed – with the exceptions of addressing co-benefits, housing/equity, economic considerations, and limited local resources to the extent desired by stakeholders due to technical and capacity building limitations at the MPO and State levels.

  • Uniform Statewide Metric
  • Regional Flexibility Recognized
  • Ambitious Achievable Targets
  • Collaborative Process
  • Existing Tools/Models
  • Policies & Practices
  • Public Engagement
  • Economic Considerations
  • Housing/Equity
  • Co-Benefits
  • Support Locals with Resources
  • Monitor and Assess Targets

Lessons Learned

California was successful in crafting ambitious and achievable GHG reduction targets largely because the political landscape had been laid throughout the state with regional Blueprint plans.  This created a foundation from which Senate Bill 375 could springboard – with many stakeholders believing that SB 375 was more of a legislative recognition of where California is on the path toward integrating land use and transportation planning.  The Caltrans Blueprint Planning Incentive Program made critical early investments in the process of regional collaboration in the RTP planning process to introduce regional governments to scenario planning through an incentive based approach.

Even California’s challenges became success stories – as the state’s major MPOs began to create an ongoing dialogue over the lack of consistency and sensitive tools/methods to measure GHG emission reduction from land use and transportation strategies.  This statewide MPO collaboration has spawned a greater dialogue related to equity and economic co-benefits from GHG emission reduction, which indicates that any federal framework that requires scenario planning could have the same benefits as a requirement to achieve a GHG emission reduction target.  However, California still struggles with state agency coordination and often encounters repeat efforts and conflicting policy objectives.  Even with the establishment of the State’s Strategic Growth Council, many of the state agencies and critical staff members focused on SB 375 implementation are not included as part of the Council.

Overall, California’s successful target setting process resulted in communication co-benefits across statewide stakeholders – a result which could not have occurred in absence of an extensive process to determine ambitious yet achievable targets.

[1] million metric tons carbon dioxide equivalent