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Arcane facts re: the EPA and the SIL ("Shift Indicator Light"):
As some of you may recall, a few weeks ago there was a thread about Saab's shift-up light, and I was adamant that it had no connection whatsoever with the US Gov't, and that it was not a factor in the EPA's CAFE (mpg) rating. I was confident that the gov't would (rightly or wrongly) trust only the behavior of mechanisms, not people. However, when reasoned opinion came in from several quarters, I started questioning my understanding of the facts. So I contacted someone at the EPA to find out what the truth is. Here's what I discovered:
* The issue was last revisited in 1983 for application re: the 1984 model year. The policies set then are still in effect. At that time, slight modifications were made to the policies that had been implemented only a year or two before. The modification to prior policy was influenced by information acquired at a September '82 EPA workshop at which input was solicited from interested auto makers. The range of opinion was all over the map, with some manufacturers being against any credit being given for SILs, others wanting liberal credit, and so on. The EPA declined to allow no credit, declined to allow maximum credit, and declined to permit the window sticker label to carry two parallel sets of mpg numbers. Instead, EPA decided to continue the previous approach of using a single number intended to represent the "average" improvement which SILs provide. Prior to this, there had not been a consistently applied methodology for determining what the average improvement might be, and the thrust of the 1983 changes was to specify how average improvement shall be determined.
The specifics of how the SIL influences EPA mpg numbers (for both estimated fuel economy window stickers and CAFE requirements) are:
* If a manufacturer so requests, the EPA tests its cars to calculate mpg numbers in two different ways. MPG is calculated the standard way, and is also calculated based on shift-points as indicated by the car's SIL. The EPA reserves the right, however, to disregard indicated shift points that seem unreasonable for actual real-world use.
* Once the two sets of mpg numbers are determined, they are factored together to produce a single set of mpg numbers. This is calculated via a simple "usage factor" which reflects the percentage of drivers that are expected to obey the SIL in actual use. For example, if there is reason to believe that 70% of drivers obey the SIL in the manufacturer's current cars, then the EPA mpg rating for the coming year's cars will be (.70 * SIL-based.mpg) + (.30 * normal-procedure.mpg).
* The usage factor is determined in any one of three ways
1. A simple survey in which customers are asked a yes/no question, "Do you usually or usually not shift with the light or before the light comes on?" For this kind of survey, a maximum usage factor of 75% is possible, even if the survey results indicate a higher percentage.
2. A more detailed survey intended to establish an actual percentage of use, e.g. "What percentage of the time do you shift with or before the light? 0-20, 20-40, 40-60, 60-80, 80-100" For this kind of survey there is no arbitrary upper limit on the usage factor.
3. If a manufacturer wants to receive SIL credit before a survey has been completed, an arbitrary usage factor of 65% is used. This requires a commitment that actual surveys will be performed and, should they produce a lower number, re-labelling (i.e., new stickers) is required. There is no provision for re-labelling should surveys produce a usage factor greater than 65%.
Regardless of which kind of survey is used, they may be conducted either by either phone or by paper surveys. Statistical adjustments are made to achieve a 95% confidence level in the case of small survey samples, such as would be the case for a manufacturer who has a small customer base. Surveys must be cleared with the EPA in advance, and must be performed anew for each model year. I am awaiting word on what manufacturers (in addition to Saab) currently take advantage of the SIL option.
I am surprised that the EPA does this, simply because they are on thin ice when they equate customer survey responses about behavior with the actual behavior itself. I cannot find any indication that there is any other provision in any of the the EPA or NHTSA procedures in which expectations of driver compliance is given any weight whatsoever. However, being surprised is quite different than being correct. Quite simply, I was wrong and several others were right.
This is probably way more than you ever wanted to know about the EPA and SILs, but after I put out the wrong story, I wanted clear things up...
posted by 216.231....
, Thu, 9 Aug 2001 09:41:29
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