Civil Engineering Reference
In-Depth Information
The most conspicuous feature of Figure 11 is how much a school bus
fleet's economics improve by combining with a transit or refuse fleet. The
payback for a fleet of 100 is 2.9 years if a school has combined with a refuse
fleet, compared to 11.5 years if they don't combine.
A second important point to be learned from Figure 11 is that the
combined fleets' payback periods are always less than the midpoint between
the two fleets. This means that combining the fleets tends to capitalize on the
relative economic advantages of each fleet while minimizing each fleet's
disadvantages. This advantage holds for the fleet that combines all three
vehicle types and has payback periods well below the weighted average of the
three individual fleets.
What Happens As My Vehicle Efficiency Changes?
CNG vehicles are generally less efficient than diesel vehicles when
compared on a BTU (or DGE) basis. However, this drop in efficiency varies
widely, depending on the specific engines and vehicles being compared.
Furthermore, this drop is being reduced as CNG technology improves and as
diesel engines strive to comply with new emissions standards. It is plausible,
but unlikely, that some fleets could compare vehicles where the CNG vehicle
is more efficient than its diesel counterpart.
Figure 12. Effects of a change in diesel/CNG vehicle efficiency.
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