Phase 3 of Project E-66 was conducted using the same engine and aftertreatment system used in Phase 1 and Phase 2, namely a 1998 DDC Series 60 heavy-duty diesel engine (HDDE) equipped with a continuously regenerative technology diesel particulate filter (CRT-DPF). Overall, Phase 3 of Project E-66 verified the greatly improved and now acceptable response time of the PFSS units tested in this program. It also showed that at a PM emission level below 10 percent of the 2007 standard, both the CVS as well as the PFSS units could be used interchangeably to produce similar results under steady-state and transient engine operation. Phase 3 of Project E-66 also highlighted the usefulness of using real time particle instruments to measure PM at near or well below the 2007 PM standard. The ease of use, high sensitivity, and fast response time (less than one second) of these instruments make them good candidates for particle measurement instead of using the filter collection technique. However, more work is needed to establish a standard protocol to calibrate and demonstrate the accuracy of these systems in measuring PM mass.