City buses from my AU:
Left 2 belong to Thessaloniki Urban Transport Organization, right 2 in Athens Urban Transport Organization. Note that half of those Citaro buses have CNG engines. Manufacturing under license program will be completed in 2021. In ELBO bus models, numbering system is "C" for city bus and ''T" for regional buses and coaches. Then follows the year when production started, eg 2012 and 2014 for the Citaro and Citaro G. All feature the most powerful engine option, with 326hp (diesel) and 295hp (CNG), coupled to a 5 speed ZF auto.
In Athens, more numerous bus was the venerable Mercedes O405N/GN, with 1,160 from 2,400 buses in its peak in 2006. About half had CNG engines. Fleet includes also latest gen MAN Lion's City and local derivatives of Volvo B7L/LA, B9L/LA, B10L from ELBO and Sarakakis factory, plus Vanhool A300/A308 diesel or CNG. These where re-engined with EURO 4 engines some years ago. In Thessaloniki Volvo and Scania almost dominated streets until 2016. Before these Citaros previous Mercedes buses where a local derivative of MB O317, in service from early 1960's to mid 1980's. These Citaros were also first CNG buses there, while Athens operates CNG buses since early 2000's. If someone wonders about, rest city buses in Thessaloniki were Scania N112/113 and a local derivative from ELBO with Steyr diesel.
Talking about city buses, most numerous city bus in HLK is the O405, followed by local variants of Volvo B7R/B7RLE, B10L(Sarakakis exclusive), B7L/B9L while older B10M (in standard and shorter 11m version) are still in service (latest 1990's B10M MkIII chassis in Sarakakis "Alexander" derivative). Other are DAF SB220 Castrosua, Vanhool A300/Α308/320 and various minibuses in cities with narrow roads.