Trolleybuses generate a lot of passion, and that passion has created a number of independent analyses of their fiscal merits. I started out somewhat lukewarm on trolleys, but this Central District News piece is pretty convincing that the operating cost of trolleys in considerably lower than that of diesels, including power line maintenance.
At current fuel price levels ($2.30 a gallon for diesel), the additional capital costs of buses overwhelm that difference. However, annual fuel price inflation as low as 7.75% is enough to neutralize that disadvantage. I’m not in the business of predicting fuel prices, but that hardly seems like an outlandish scenario. Moreover, there’s a substantial tail risk of a steep rise as in 2008. That was a financial catastrophe for Metro then, and it would be nice to have an important segment of the system be immune to it in future.
There is one other factor not in the analysis that is pertinent to the budget: availability of capital funds. For whatever reason, the federal government almost always funds capital costs rather than delivering a direct operating subsidy. For that reason, it generally makes sense to assume a little more capital cost if it reduces operating expense.
Of course, there are also externalities (diesel pollution, street damage, noise, etc.), but those aren’t in Metro’s budget and perhaps it’s unfair to ask a cash-strapped agency to alleviate those problems.