A couple of e-mails came in over the weekend about the Examiner story on Proposition I, the March ballot battle over polluting diesel buses. Readers want to know whether biodiesel alternatives have been explored for the old buses – particularly since some can’t even be upgraded with pollution filters. The biggest controversy with Prop. I, it seems, is the reserve fleet and its replacement costs vs. overuse. Under Prop. I, the reserve fleet would have to be replaced, even if it could be made cleaner with biodiesel. These kinds of controversies are best worked out through the legislative process, which is why The Examiner is generally opposed to legislation rammed onto the ballot by four supervisors, as happened with Prop. I. More on biodiesel and Muni later.