The parallel hydraulic hybridization, thanks to its simplicity and high specific power, is a suitable solution for the retrofitting of off-highway vehicles subject to work cycles with frequent stop-and-go. This work is focused on the potential of the low-cost parallel hybrid solutions, i.e. characterized by current-technology components, for a specific class of heavy vehicles: city buses. After functional sizing, the hybrid vehicle was modelled and simulated in the Amesim environment. The comparison with the non-hybridized reference vehicle highlighted an interesting consumption reduction, which in any case varies with the type of route. Finally, an optimization of the hybrid vehicle was carried out by means of genetic algorithms, which led to a further, and not negligible, consumption reduction compared to the hybridized version. Optimization, therefore, can be seen as a tool to overcome those minimum benefit thresholds that manufacturers consider as necessary for the industrialization and marketing of new energy recovery systems.