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EPA Testing Methods
EPA gas mileage standards were originally developed based on a mid-1960s project where surveyors were sent to all major United States cities to discover the conditions of a typical commute. Traffic was much lighter at that time, and the highway test did not exceed 70 mph. Thus, the test was, before 2008, optimistic for most cars, and applying a simple correction factor would result in more bias. The 2008 and newer test is more realistic for most drivers, including air conditioning, faster speeds, and more time spent stopped at simulated traffic lights.
EPA Federal Test Procedure (FTP75) for emissions compliance
(Posted by Mark Shaw Around 1994; 2008 methods are similar but with some variations)
These are done on only a few vehicles of each model. The test is run on a simulated driving cycle lasting 2,477 seconds and 11.1 miles. It starts with a cold start after an overnight cool down (12 hours) at an ambient temperature of 20-30C. Test includes a shutdown for 10 minutes with a repeat of the first 505 seconds after a hot restart.
The overall average speed is about 21.1 mph with maximum of 56.7 mph, and around 17.9% of the time, the engine is at idle.
The measurement method uses diluted air with a makeup pump supplying a known quantity. Samples of known percentage are collected in bags during various phases of the test. Total mass of each emission is calculated and averaged over the total test distance for data in grams/mile.
There are some adjustments made for the weight (for dynamometer loading) and total diluted air to be included.
For more detail see the SAE Handbook, Section 13. Particularily the following standards/practices: J254, general testing; J1094 - CVS testing; and J1506 - the FTP75 driving cycle.
Test limits are expressed in grams/mile and depend on class, weight, and year. Generally, light trucks are allowed 1.5-5X what passengers cars are allowed (this was phased out). Heavier versions of light duty trucks are allowed even more. For the 1981-1995 model years which are subject to local IM240 testing the limits look like:
EPA gas mileage standards were originally developed based on a mid-1960s project where surveyors were sent to all major United States cities to discover the conditions of a typical commute. Traffic was much lighter at that time, and the highway test did not exceed 70 mph. Thus, the test was, before 2008, optimistic for most cars, and applying a simple correction factor would result in more bias. The 2008 and newer test is more realistic for most drivers, including air conditioning, faster speeds, and more time spent stopped at simulated traffic lights.
EPA Federal Test Procedure (FTP75) for emissions compliance
(Posted by Mark Shaw Around 1994; 2008 methods are similar but with some variations)
These are done on only a few vehicles of each model. The test is run on a simulated driving cycle lasting 2,477 seconds and 11.1 miles. It starts with a cold start after an overnight cool down (12 hours) at an ambient temperature of 20-30C. Test includes a shutdown for 10 minutes with a repeat of the first 505 seconds after a hot restart.
The overall average speed is about 21.1 mph with maximum of 56.7 mph, and around 17.9% of the time, the engine is at idle.
The measurement method uses diluted air with a makeup pump supplying a known quantity. Samples of known percentage are collected in bags during various phases of the test. Total mass of each emission is calculated and averaged over the total test distance for data in grams/mile.
There are some adjustments made for the weight (for dynamometer loading) and total diluted air to be included.
For more detail see the SAE Handbook, Section 13. Particularily the following standards/practices: J254, general testing; J1094 - CVS testing; and J1506 - the FTP75 driving cycle.
Test limits are expressed in grams/mile and depend on class, weight, and year. Generally, light trucks are allowed 1.5-5X what passengers cars are allowed (this was phased out). Heavier versions of light duty trucks are allowed even more. For the 1981-1995 model years which are subject to local IM240 testing the limits look like:
Year For Cars HC CO NOx Total 1981-95 0.41 3.4 1.0 4.81 1994-95 0.25 3.4 0.6 4.25 (1994 starts phase in of Tier I standards, completed by 1996)