Air Quality & Emissions, California, SB 375

An alternative approach to setting SB 375 targets

Bay Bridge toll plaza

Bay Bridge toll plaza. Courtesy of gohsuket.

Earlier this month, agency staff at the State Air Resources Board (ARB) recommended a set of targets, which quantify how much regions throughout California should plan to reduce greenhouse gas emissions from passenger vehicles and light duty trucks.  Those targets will soon be evaluated by the Board, which is required under Senate Bill 375 to adopt a final set of regional targets next month.  The proposals suggest per capita targets measured from a year 2005 baseline: 7-8% reduction in 2020 (13-16% in 2035) in California’s urban areas by 2020, and 5% reduction in 2020 (10% in 2035) in the San Joaquin Valley.

In a previous post, we asked whether these targets would be good enough to put California on the path to achieving its stated goals: (1) Assembly Bill 32’s requirement that emissions be reduced to 1990 levels in 2020, and (2) achieving emissions 80% below 1990 levels in 2050.  By estimating combined GHG reductions from SB 375, the Pavley standards, and the Low Carbon Fuel Standard, a few calculations suggested that although ARB’s proposed targets for 2020 were good enough, the targets for 2035 may be too restrained to realize the desired reduction in emissions.  But if the ARB target isn’t good enough, then what is?  How much would we need to reduce driving in California in 2035?

Following the reasoning in the previous post, another calculation suggests that a 37% per capita VMT reduction target will achieve the desired greenhouse gas reductions in 2035:

(1 – 0.37)(1.36)(1 – 0.1)(1 – 0.32) = 0.524

In other words, there would be a 48% combined reduction, which is good enough to keep California on track in meeting its 2050 goal (assuming a linear model of emissions reduction between 2020 and 2050).  But this 37% target represents a weighted statewide average.  In reality, there would be distinct regional targets.  ARB’s regional targets are based on the analysis supplied to it by California’s metropolitan planning organizations (MPOs).  But as we have seen, MPO suggestions may not be good enough — so what is an alternative approach?

Growth-Based Regional Targets

One possible way to distribute the responsibility among regions is by growth rate: The faster a region is growing, the more it could be held responsible for reducing its vehicle emissions.  Please note that this is not the approach ARB has adopted to date.  The rapid growth of San Joaquin Valley is expected to outpace the rest of the state by far, and yet, the Valley MPOs have been assigned a target that is less ambitious than those assigned to urban MPOs.  That said, the Valley placeholder target is essentially a ballpark estimate, offered so that ARB can comply with the legislative deadline.  It is subject to change in the next few years, but it is too soon to tell whether it will ultimately be more ambitious, less ambitious, or simply stay the same.

How would growth-based targets compare to ARB’s proposals?  We first make the simplifying assumption that regions uniformly achieve the state’s overall reduction objective.  Then, taking into account each individual region’s projected growth, we can calculate a new set of per capita regional targets for the year 2035. In the table below, the growth-based targets are listed in the middle column, and ARB’s proposed targets are provided in the right column:

Growth-Based Target
ARB Proposed Target
Los Angeles
Bay Area
San Diego
San Joaquin
Valley total
Monterey Bay
San Luis Obispo
Santa Barbara
Tahoe Basin

Using a growth-based methodology, the table quantifies approximately how much, on average, citizens of each metropolitan region would have to reduce their driving in order to keep California on track to meet its stated climate change goals.  The table suggests that very substantial reductions in driving will be necessary.  The growth-based targets are significantly more aggressive than the ARB proposal — unrealistically aggressive under current practices — because rather than passively accepting MPO data, this approach is specifically designed to be more proactive in achieving emissions 40% below 1990 levels.  In other words, these growth-based targets are “top down” rather than “bottom up.”

Comparing the absolute reduction in emissions for these growth-based targets vs. ARB’s proposed targets is also rather dramatic.  According to ARB, its proposed targets would realize a 15.1 MMTCO2 (million metric ton) reduction per year from 2035 baseline emissions.  In contrast, the growth-based targets would realize a 51.9 MMTCO2 reduction from the 2035 baseline.

The next post will consider some implications of developing growth-based targets.  For now, we note only that achieving these targets would require an unwavering commitment to crafting smarter land use patterns, expanding high-quality transit networks throughout the state, calling a moratorium on the construction of new roads, and implementing aggressive pricing mechanisms that encourage motorists to shift travel modes.  At the present time, MPOs might conclude that such measures are politically unpalatable, and thus decline to pursue some of them.  But they may ultimately prove to be necessary if California is to be successful in achieving its climate change goals.



6 thoughts on “An alternative approach to setting SB 375 targets

  1. Why are per-capita decreases in driving weighted towards high-growth rather than low-growth regions? I would imagine that high-growth areas would need a more flexible ceiling to avoid stifling the growth needed to densify their regions, whereas the low-growth areas already have a density that would support more intense transit development.

    Posted by OctaviusIII | 19 August 2010, 2:06 pm
  2. Hi Octavius,

    These targets make a simplifying assumption that regions uniformly reduce their vehicle emissions, so places that are growing faster would have to compensate accordingly. As you mentioned, there are difficulties with this approach that I hope to get into some more in an upcoming post.

    Another thing to keep in mind is the timescale, in that one could expect more reduction in the short-term from more developed urban areas, while targeting higher reduction from fast-growing areas in later years. There is more flexibility in terms of setting and accomplishing goals in the 2035-2050 timeframe than there is in the 2010-2020 timeframe.

    I should clarify that the point of this post is not to advocate for these exact numbers, because there are any number of policies you could advance when allocating targets among the regions, and those policy choices will give you different numbers. Rather, the point here was mostly to illustrate that whatever scheme you do go with, the “ambitious” targets offered to date probably won’t do the job because they aren’t tied to absolute GHG reduction objectives.

    Posted by Eric | 19 August 2010, 3:02 pm
  3. hey, thanks for posting this! i think “peak resources” and domestic collapse/war will greatly aid us in reaching these old lows. maybe i am pessimistic.


    Posted by Ken O | 19 August 2010, 9:39 pm
  4. It’s funny: because of high gas prices a couple years ago and the ongoing recession, there have actually already been per capita VMT reductions that are in line with ARB’s proposed 2020 target (-7 to -8% in urban areas). Probably not quite that high, but in the ballpark — and that’s before any intense land use changes, before congestion pricing, and without expanding transit capacity. That was just people responding to changed circumstances.

    Of course, the trick is to sustain that reduction over a longer time-scale, through 2020, even when the economy bounces back. The more catastrophic events you mention would certainly have an effect, but even without those, there is room to reduce.

    Posted by Eric | 19 August 2010, 10:03 pm
  5. This is some of the most in-depth information I’ve found for alternative targets in the Bay Area. If SB 375 really is a ‘process’ then we’ll need this kind of thinking when we revisit our targets in the coming years. Keep up the good work!

    Posted by Brant | 21 October 2010, 10:25 am
  6. Eric,
    Spot on about percapita assessment! Percapita is part of the issue, but the real issue is the quality of our air. We need to lower aggregate GHG emissions. Agree whole heartedly about the top-down approach. If we are going to attack our climate problems we need to look at where we need to be, and then get there.

    2009 GHG were down because of the economy (less freight, less people commutting, less family vacations ect)

    Great post!

    Posted by Brian B. | 26 October 2010, 9:42 am

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