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III. Smog and congestion impacts of different congestion- and emission-charge strategies

The Appendix compares estimated yields and costs of 16 different congestion- and emission-charge strategies under assumptions described in Section I above. Their cost and yield estimates are drawn from three sources: (1) the Wilbur Smith Associates/Comsis studies performed for the REACH Task Force, applying congestion charges to freeways only; (2) the author's extrapolations of WSA estimates to include surface streets, as well as freeways; and (3) estimates by Elizabeth Deakin and Grieg Harvey for the California Air Resources Board (CARB) (CARB, 1995; see also Cameron, 1994, Harvey, 1994). For further details, request the longer version of this article.

The WSA estimates modeled traffic specifically on every freeway, but globally on surface streets, none of which were charged in the model. The Deakin-Harvey estimates modeled traffic globally for all roads in the Basin but, unlike WSA, applied congestion charges both to freeways and surface streets. Thus, the two basic models, WSA and Deakin-Harvey, had contrasting strengths and weaknesses. WSA looked stronger and more detailed on freeways, but weaker on surface streets, and weaker in its inability to model for charges on surface streets. Deakin-Harvey was broader, much less detailed about freeways, much more detailed about impacts on different economic classes, and able to model globally for charges on surface streets. Deakin and especially Harvey were reticent about their modeling assumptions, and Harvey died shortly after the Task Force shut down, leaving many loose ends. But some of the missing assumptions could be gleaned from earlier, more explicit Harvey studies, such as Harvey, 1994, and Cameron, 1994. Others have been borrowed or adapted from WSA and other sources. The notes to the Appendix discuss a number of such borrowings and adaptations, attempting to make the two studies as comparable with each other, and with available planning documents, such as the AQMP and the SCAG RTIP, as circumstances would permit. Though the comparisons and adaptations are far from perfect, the two main studies are generally consistent with each other and with the planning documents. They and the two landmark 1994 studies, by Cameron and by the Transportation Research Board, put transportation planners far ahead of where they were prior to 1994. They do present a valuable, coherent, instructive set of approximations of the most probable impacts of emissions, congestion, and mileage charges of varying levels.

The Appendix gives an overview of all the impacts, costs and yields, with most impacts presented both in percentage variation from baseline and in dollar values. These are: $9,000 per average ton for TOG; $10,000 per average ton for NOx; $21,000 per average ton for PM10; and $6.80 per average person hour for travel time. Readers are free to experiment with different figures, but these are as close to the "going rates" as are likely to be found, and they are, for the most part, the same rates currently in use for regulatory cost cutoffs (See Section I above).

Figure 1: Gross Smog Reduction Benefits, 2010, Selected Strategies

Figure 1: Gross Smog Reduction Benefits, 2010, Selected Strategies

Figure 1 (above) breaks out the estimated smog reduction yields of seven of the 16 strategies. A penny-per-average-mile emissions charge, variable by the emission level of each car, is about as high as the current "going rate" cost cutoffs for industrial polluters. By itself it would control more than $100 million worth of smog per workyear. So would a 15/30-cents a-mile peak-hour congestion charge on all roads, also by itself, assuming the charges had the same impact on surface streets as WSA calculated for freeways (See Appendix). A lower, freeways-only congestion charge would control just under $100 million worth of smog per workyear. Conclusion: either reasonable, "going-rate" emissions charges or reasonable congestion charges could cut smog damage by at least about $100 million a workyear. Deakin and Harvey say the control yield could be more than twice that figure for a 1-cent/mile emissions charge (Appendix), but let us leave that aside for the moment and suppose that $100 million is a conservative, round-number guess for the yield of either strategy by itself.

Figure 1 also says that a combination of reasonable-rate emissions charges and congestion charges would produce at least $200 million worth of annual smog savings, and maybe well over $300 million. $200 million is about equal to the officially-estimated control yield of mandatory ridesharing.

Figure 2 (below) is in some ways the most plainly revealing of pertinent tradeoffs. See Glossary, below, for full definitions of the various strategies. WSA means 'Wilbur Smith Associates." EM1 means "first emissions-charge variant." CP1 means "first congestion pricing variant," freeways only. WE means "Ward Elliott." CP3+ means "third WSA congestion-pricing variant, extended to surface streets." D-H Mod Combo means "Deakin-Harvey 'moderate-impact' combination." ET means $12.5 billion worth of "enhanced transit."

Figure 2: Gross Smog, Congestion Benefits, 2010, Selected Strategies

Figure 2: Gross Smog, Congestion Benefits, 2010, Selected Strategies
Figure 2: The three modeled congestion-charge alternatives that cover freeways and surface streets could save billions of dollars a year in smog and congestion costs. In dollar value, at least 90% of the savings would be congestion costs. Even a penny-a-mile charge, aimed solely at smog, would save four times as much cost from congestion as it would save in costs from smog alone.


Figure 2 compares the yields of the same seven strategies as Figure 1, but with congestion-control benefits included, as well as emission-control benefits. Two features stand out:

    (1) none of the official WSA scenarios listed -- neither the reasonable, penny-a-mile emissions charge, which affects all roads, but is not time-specific, nor any of the congestion-charge combination scenarios, which are time-specific but affect freeways only -- has much effect on speed.

    (2) the two scenarios combining reasonable penny-a-mile emissions charges with reasonable 10-30-cents-per-peak-mile systemwide congestion charges show enormous time savings, about 15 times greater in dollar value (at $6.80 per person hour per Section 1 above) than the very sizeable smog savings (at $9,000 to $21,000 per ton per Section 1) also produced. The lower estimate, WE CP3+, EM1, would save 680 million person hours a year, the higher, D-H mod, would save 950 million person hours a year (calculated from the Appendix). A third scenario, with 15-30-cents systemwide congestion charges, but no emissions charge at all, equals the WSA penny-a-mile emissions charge in smog reduction and produces 30 times as much savings from congestion relief. In each case, the higher figure (e.g., 30 cents a mile) is the charge for currently crowded links, the lower (10 cents a mile) is a "balancing" charge to keep traffic in charged crowded links from simply shifting to uncrowded links.

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