A graph shows a potential timeline for CTA’s electrification of its buses.

The process of switching the city’s fleet from diesel to electric-powered vehicles is slow moving as the city makes plans to phase out old vehicles and waits for federal funding to be unlocked to move the process along, according to information presented Tuesday during a City Council committee hearing. Still, the CTA has charted out an aggressive plan to electrify its bus fleet during the course of the next two decades, agency officials said.