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| How MDBF is Figured (was:Worst NYC subway car MDBF rating ) (432422) | |||
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How MDBF is Figured (was:Worst NYC subway car MDBF rating ) |
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Posted by Train Dude on Fri May 18 19:05:34 2007, in response to Re: Worst NYC subway car MDBF rating (2006 year) goes to.., posted by Mitch45 on Mon May 14 12:18:18 2007. MDBF stands for the MEAN DISTANCE BETWEEN FAILURES!The computation is matematically simple - The number of miles traveled/# of failures for the same period of time. MDBF can be computed for a single car. A single class of cars, a single car fleet, a single shop fleet or the entire fleet. For example: The Jamaica shop fleet accumulates approximately 6 million miles per month. If they have 30 charged delays during that month the MDBF is 6,000,000/30 or 200,000 miles. If the R-46s accumulate 4.5 million miles during that month and have 15 charged delays then their MDBF is 300,000 miles while the R-32s with the remaining 1.5 million miles and 15 remaining delays would mean an MDBF of 100,000 miles. The MDBF numbers posted appear to be the 12 month moving MDBF numbers for individual car classes. This is the most accurate indicator of overall performance because it mutes one-month spikes or plunges in the MDBF statistics. It's hardly a perfect measure but it does accurately reflect relative performance of various fleets and shops. The hardest part of the MDBF equation to understand is the determination of what delays are charged and what delays are not. Not every incident of mechanical failure gets charged to car equipment and in some instances car equipment gets charged for delays that are unrelated to car performance. |
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