Evaluating Vehicle Emissions Inspection and Maintenance Programs (2001) / Chapter Skim
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6 Evaluating Inspection and Maintenance Programs: Methods for Estimating Emissions Reductions
6 Evaluating Inspection and Maintenance Programs: Methods for Estimating Emissions Reductions
Pages 146-168
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From page 146... ...
Difficulties in estimating emissions reductions arise because vehicle emissions are variable over time and with driving method, emission tests themselves are variable and imperfect, and perhaps most important, the behavior of motorists, technicians, 146
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From page 147... ...
METHODS FOR MEASURING EMISSIONS REDUCTIONS There are several inherent difficulties in evaluating the emissions reductions from an I/M program. One is defining the baseline, the condition against which the I/M program is compared.
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From page 148... ...
Because of these issues, the approaches for evaluation described in this chapter include data needs and methods that attempt to account for all the factors that influence emissions reductions technical, behavioral, and others. All the categories of emissions reductions listed in Table 6-1 must be evaluated to determine the effectiveness of a program.
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From page 149... ...
As aresult,although many tailpipe emissions data are available, there are no evaporative emissions measurements that directly measure I/M effectiveness to reduce all sources of non-tailpipe emissions. As discussed in Chapter I, evaporative emissions represent a significant but unquantified source of overall vehicle HC emissions.
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From page 150... ...
That is a problem if it is assumed that all vehicles are tested and that failing vehicles receive repairs yielding some average emissions reduction. Owners might collude with technicians running the test program to falsify the emissions level of a failing vehicle so that it passes.
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From page 151... ...
year ~ 98 ~ and ~ 982 vehicles and is plotted on a logarithmic scale to reduce data scatter. Data from Roadside Testing Exhaust emissions test data can also be obtained from vehicles subject to roadside tests.
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From page 152... ...
EPA' s national tampering surveys, conducted from the late ~ 970s through ~ 992, measured about 7,500 vehicles per year between lL985 and 1992. Because ofthe costs and time required to perform roadside testing and for political reasons, emissions on far fewer vehicles are measured in this manner than are measured in the inspection lanes.
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From page 153... ...
Roadside testing coupled with a vehicle's I/M history can demonstrate the effectiveness of an I/M program or changes to a program, the duration of repairs, the occurrence of pretest repairs, the level of compliance with the program, and whether there is a need to increase enforcement. Data from Remote Sensing Remote sensing is a third source of tailpipe emissions data (see Chapter 4 for a Ascription of remote sensing)
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From page 154... ...
Remote sensing can also determine the percentage of vehicles exempt from testing but Diving in the I/M area, together with an estimate oftheir contnbution to overall vehicle emissions. Data on Evaporative Emissions The evaporative emissions reductions possible from periodic inspection and repair programs are difficult, if no/impossible, to estimate.
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From page 155... ...
found in a California study that on average vehicle emissions ofthe repaired vehicles returned to their original level after 2 years. There is also evidence that some emission reductions lastformuchiongerperiods.
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From page 156... ...
Critiques of this method are discussed in the following section. An advantage ofthe reference method is thatit canbe applied at any point during the program' s lifetime as opposed to only when there is an incremental change in the program (as with the step method of evaluation described below)
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From page 157... ...
This guidance for I/M evaluations of state programs also was discussed in the I/M Program Evaluation Panel at the ~ 6th Annual Mobile Sources/Clean Air Conference, September 2000, sponsored by the National Center for Vehicle Emissions and Safety at Colorado State University. Richard Joy, of Sierra Research, stated that previous applications ofthe EPA Guidance on I/M program evaluation were not valid because vehicles in the benchmark pro gram in Phoenix were not uniformly preconditioned.
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From page 158... ...
differences, and other factors might be responsible for the differences in vehicle emissions reductions. Such factors are not accounted for or estimated in the current EPA guidance for evaluating I/M using the EPA-approved method.
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From page 159... ...
The step method can be applied to estimate the impact of a change to an I/M program or to estimate the deterioration in vehicle emissions from one test cycle to the next. Comprehensive Method In this method, vehicles are split into groups according to their test results: initial pass, faiVpass, faiVwaiver, and faiVno-pass (see Table 6-2~.
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From page 160... ...
Methods for Estimating Emissions Reductions From Induced Fleet Change In some cases, the methods descnbed above will provide estimates of emissions changes resulting from both vehicle repair and changes in the makeup of the fleet. The step method can evaluate both of these effects.
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From page 161... ...
If motorists do scrap their vehicles early because of I/M, the resulting emissions reductions depend on what the vehicles' remaining lifetimes would have been without I/M and the difference in emissions between the scrapped vehicles and the replacement vehicles or alternative transportation modes. If a scrapped vehicle is marginal rather than a high emitter, the emissions reduction induced is not large.
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From page 162... ...
Induced Relocation Motorists or dealers might sell vehicles outside the region rather than pay large repair bills. These vehicles can be treated just like the scrapped vehicles described above forthe purposes ofthis analysis, if itcanbe demonstrated that they do indeed remain outside the program area.
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From page 163... ...
We distinguished between these fail/pass cars and the fail/pass cars that do not get repairs but rely on improved preconditioning or the variable nature of vehicle emissions to pass an emissions test after initially failing.
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From page 164... ...
Besides providing for an estimate ofthe emissions reductions, comprehensive evaluations could tee usedby all programs to improve forecasts of I/M benefits from the MOBILE and EMFAC models and to assess the potential emissions impacts from changes in program design. Full evaluations could also be used to help less comprehensive program evaluations estimate allpotential sources of emissions impacts due to I/M.
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From page 165... ...
There is no perfect method for evaluating all emissions impacts from I/M the reference, step, and comprehensive methods all have their own inherent limitations. The ideal evaluation is a reference method comparing an I/M area with a non-~/M area, which would take into account normal repair (from the non-~/M area)
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From page 166... ...
A review committee should be established to advise EPA in the selection of shortened evaluation methods and in selection of what information can be drawn from comprehensive evaluations to inform the shortened evaluation.
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From page 167... ...
States conducting comprehensive evaluations oftheirI/M programs also should do a shortened evaluation. EPA will review the differences between the results ofthe comprehensive evaluation and the shortened evaluation and will modify the shortened evaluation method so that its results are more similar to the comprehensive evaluation" Validation of the shortened evaluation should be done at least once every 3 years.
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From page 168... ...
Over time, alternative programs to reduce in-use vehicle emissions might be developed by states. Systems that rely exclusively on remote sensing or OBD may be used as technology improves in the future.
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