They Say: The Spare Ratio is 20%December 30, 2011 by: Samuel Scheib
The question comes up all the time in the transit business: why doesn’t your transit agency does not deploy smaller buses? This question has been posed to me so many times now that my answer is reflexive and automatic. For those not intimately plugged into the transit business there are four reasons:
Capacity. There is no savings. There is no money for a second fleet. FTA won’t let us.
I just realized, however, that one of my arguments was flawed.
The first point is usually the reason people are asking the question to begin with, because they see “empty” buses going by “all the time,” and capacity is the most important and easiest reason to explain: We can run a large bus empty in the off peak, but we can’t run a small bus bigger during the peak.
I then explain the most expensive part of operating a bus is the driver and that we pay the same salary regardless of the vehicle size. Additionally, a recent study by CUTR found the average annual miles per gallon consumed on small buses to be 3.8 versus 4.3 for large buses, an improvement of only 12%, and the average annual per-mile maintenance cost (labor and parts) was actually a penny more for small buses ($1.26 vs $1.25 for large). Even the savings of purchasing a small bus was insignificant, only $20,000 (8%) over a forty footer. Whatever small savings a transit property gets from buying and using smaller buses is, however, unimportant during the peak when buses are full and capacity is the main problem.
Of course, with the constant need to replace buses expanding a fleet by only a few buses to increase service is a challenge. Buying a whole separate fleet of shorter buses to run during off peak hours is not feasible (read: impossible). TCRP Synthesis 11: System-Specific Spare Bus Ratios puts a nice point on it:
“Especially in the cost-conscious environment of public transit, the fleet manager cannot be burdened with a fleet that includes vehicles that are not carrying their full share of the demand, or buses whose unit costs bring down the overall productivity of the fleet. Managing fleet size in relation to service levels is smart management and is also fiscally responsible. Transit managers use the performance measurement known as spare ratio as one indicator of their status in this important area.”
So far, so good. Then we get to the 800 pound gorilla, the Federal Transit Administration. We always hear there is a spare ratio imposed by FTA that says properties cannot have out of service spares on the lot in excess of 20% of our peak-hour vehicles (technically, VOMS, or vehicles operating in maximum service). But in checking FTA Circular 9030 1A (1987) we find it says,
Spare ratios will be taken into account in the review of projects proposed to replace, rebuild or add vehicles. The basis for determining a reasonable spare bus ratio should take into consideration specific local service factors. The number of spare buses in the active fleet for grantees owning fifty or more revenue vehicles should normally not exceed 20 percent of the vehicles operated in maximum service. For purposes of the spare ratio calculation, “vehicles operated in maximum service” should be in accordance with the definition of this term under the Section 15 reporting requirements (49 C.F.R Part 630). (emphasis added).
A requirement would have a “must” or “shall” in there rather than the less demanding “should not normally,” so there is some wiggle room there. At the same time, 800 pounds is pretty big and no transit agency wants to pick a fight with FTA, so 20% has become the industry norm. And anyway, the first three points are answer enough for your inquisitor why you don’t buy tiny buses.