(03 Aug 2014, 11:06 am)cumbria0902150 wrote Extra capacity, less road space, but they cost roughly £40k-50k more than a single decker, they cost more to run, can cost more to insure due to the risk of tree/bridge strikes, and depending on type they often can't match the efficiency of a single deck due to the same rated engine, or sometimes detuned engine, lugging more weight around, so for the operator there's usually more lost than they'd often gain. Very easy to see why some operators will only buy double decks if they're really needed or they can clearly justify the additional costs.
Even though Stagecoach own their own insurance company, everything still has to be done above board to satisfy the regulators, so they can't just reduce the insurance costs to suit.
But if your customers are packed like sardines on a single decker, doesn't that provide the justification to provide a double decker? It's either that or the frequency needs looking at, which can often be more expensive than just providing double deckers in the first place...