Development of the IM147: An Alternative Inspection/Maintenance Mass-Emission Transient Test to Address Vehicle Preconditioning Concerns

Abstract

A series of studies was performed to develop an alternative to the U.S. Environmental Protection Agency's gold standard IM240 mass-based emission test. The new IM147 test was based on the second phase of the IM240 that consists of 147 sec of transient vehicle operation. Paired IM240/ IM147 tests were conducted on vehicles ranging from 1981 to 1996 to determine IM147 cutpoints and excess emissions were identified. Additionally, an optimized test procedure was developed that combined possible triplicate IM147s with improved drive trace quality control, fast-pass, and retest methods. The optimized procedure was found to provide improved vehicle preconditioning with a relatively minor decrease in excess emissions identification. Resulting identification rates ranged from 96 to 100% for hydrocarbons (HC), 93-100% for CO, and 93-100% for NO x , depending on cutpoint selection, while false failures caused by lack of vehicle preconditioning were reduced to essentially zero. Significant vehicle throughput improvements were achieved through the development of software algorithms involving modal fastpass and retest procedures. Modal drive trace variation limits also were developed to improve test accuracy. The combination of the algorithms reduced average IM147 test times by nearly 60%.

Regulating Untaxable Externalities: Are Vehicle Air Pollution Standards Effective and Efficient?

“…While many states test vehicle emissions, recently only Colorado has used the highest-quality test, called IM240 (the inspection and maintenance test that lasts 240 seconds). This test provides a short version of the Federal Test Procedure and is considered the "gold standard" of smog check tests for its quality and comparability to the Federal Test Procedure (Sierra Research 1997;Joy et al 2004;U.S. EPA 2006); Appendix B.1 discusses this comparability.…”