The Optare Sigma was powered by the Cummins C-platform engine, while the Optare Excel was powered by the Cummins B-platform engine.

Like the Metrorider, the Excel was also available with an Allison transmission.

The Sigma and it’s successor-the Excel are midsize buses, whereas the Metrorider is a compact-sized bus.

Videos of the Optare Sigma and it’s successor-the Excel: