>make bigger buses Nontrivial after adding the second deck (common in UK & Hong Kong), or an articulation (common in EU and mainland China) However for tram, t

>make bigger buses Nontrivial after adding the second deck (common in UK & Hong Kong), or an articulation (common in EU and mainland China) However for tram, the upper limit is your platform length. It's also common to run single trains off-peak, couple two together during busy hours to double the capacity.