Quick clarification

Are you suggesting that these shifts should be considered because people might drive the same distance, but with less sitting in traffic, thus less environmental impact?I could see maybe arguing for this if you really think there is reduced impact for the project, but I wouldn't count on it getting approved.

The SCAQMD specifically defines the "peak window" as the period of time, Monday through Friday between the hours of 6:00 AM and 10:00 AM, and used in calculating the vehicle trip emission credit.

o Per SCAQMD: Employees that do not report to the worksite during the 6:00 a.m.-10:00 a.m. window should not be included in the AVR calculation. Employees that are reporting as being on vacation, or sick, are accounted for but not included in the AVR equation. Per-diem or on-call employees (that do not meet the definition of field personnel) are not included in the AVR calculation unless they report to the worksite during the window at the time the survey is conducted.

Just to clarify, in the situation Wendy has described above I agree that the late-shift commuters are not automatically considered alt transport users due to the timing of their commute, but I want to be sure the SCAQMD notation about employee shifts isn't overextended here. As noted elsewhere, if you're in the SCAQMD you can follow their rules 100% without penalty/question, but if you aren't, some discretion and consideration of credit intent is really important. From a LEED standpoint, a commute is a commute, whether it happens at 8am or 11am or 8pm - Commutes for all shifts should be included and accounted for in your SSc4 analysis. Although SCAQMD's primary concern is air quality (and therefore commutes during rush hour are of paramount concern), EBOM's primary concern is GHG emissions which are not nearly as dependent on commute timing (as Tristan notes, beyond the marginal additional pollution created by traffic delays.)
Dan