An Evaluation of a Colorado Short Vehicle Emission Test (CBH-226) In Predicting Federal Test Procedure (FTP) Failures

Increasingly stringent Federal exhaust emissions standards being applied to new automobiles necessitates an accurate short test to indicate vehicle emission failures for Inspection Maintenance (I/M) Program purposes and to trigger the Emission Control System Warranty provided in Sections 207 (a) and 207 (b) of the Clean Air Act. It was the intent of the Colorado Department of Health to develop a test that would accurately identify excess exhaust emissions and have an acceptable mathematical correlation to the results of the Federal Test Procedure (FTP). In an attempt to decrease the errors of omission exhibited by existing short tests, a short loaded mode, mass emissions test was considered. A basic statistical analysis of the EPA Urban Dynamometer Driving Schedule was performed and a 226 second driving schedule was developed. This driving schedule was entitled the CDH-226.

The CDH-226 has been performed on one hundred seventy six (176) 1981-1984 in-use vehicles at high altitude. The results discussed in this paper are a statistical comparison of the CDH-226 with Federal Test Procedure results. The CDH-226 shows a high positive mathematical correlation to the FTP for hydrocarbons, carbon monoxide and oxides of nitrogen and proves to be an accurate identifier of excess emissions for all three regulated pollutants.