The energy required to move a vehicle is a function of rolling resistance, aerodynamic drag, the number of
times the mass of the vehicle has to be accelerated, the size of the mass being accelerated, the length of the
route, the thermal efficiency of the conversion processes, and, in the case of rail mass transit, an often near-
empty back haul.
- Because when the electric car is on the smart cart which has steel wheels, we have steel wheels on
steel rail and the rolling resistance is reduced significantly—typically 50% of that of rubber tire on concrete
roadway.
- At urban speeds aerodynamic drag is not a big factor, but there is no reason to think that overall
SEGway aerodynamic drag would be much different than an automobile.
- In terms of the number of accelerations, SEGway will have far fewer, due to avoiding highway
congestion, and both the smart cart and the electric car would have regenerative braking. Of all the energy
requirements of motion, accelerations in urban driving is dominant and SEGway excels here relative to the
automobile.
- Concerning mass: The electric car will not have a heavy battery pack because it doesn’t have to go
long distances by itself, and it will not have an engine, cooling system, and fuel system. The smart cart
will be quite light, only a platform with wheels, one or two small motors, and electronics console. So a
smart cart with an electric car on it may weigh no more, or at least not much more, than a conventional car.
- There is nothing to say that the length of a trip via SEGway will vary from the automobile trip
connecting the same origin and destination, on average.
- In terms of thermal efficiency, recent dynamometer tests by Argonne National Laboratory’s Center
for Transportation Research show that in urban driving an electric car is substantially more gallon
equivalent efficient than a gasoline fueled automobile. Certainly an electric car on a smart cart will be far
superior because the energy does not have to go through two electrochemical conversions as when the
electric car’s battery is charged and discharged.
- Empty backhauls: Unlike radial rail transit lines, SEGway will eventually be a network. When you
look at urban trip pattern data you see that the inbound to the central city in the morning and the outbound
in the evening trips are but a fraction of the total trips. The number of reverse commute trips is substantial
and growing. Radial rail transit fails to capture many reverse commutes because once at the suburban
station, the commuter has little choice of how to get to the work site. Suburb to suburb commutes are the
largest portion of commute trips. However, until we are able to do some simulation, we cannot estimate
the percent of smart cart miles that will be empty, but I expect with good smart cart management, it will be
small, especially with a good pricing scheme and a few strategically located smart cart storage areas.
Never-the-less, moving an empty light-weight smart cart around will not be energy intensive.
A typical small electric car has an energy intensity of about 0.2 kWh/mi in urban driving. Given that when
it is on the smart cart it is in a steel wheel on steel rail situation and that the electricity does not have to go
through two electrochemical conversions, the energy intensity of the smart cart with electric car should be
better than 0.2 kWh/mile (about 2¢/mi.).
All the energy arguments made have been based on passenger movement. A similar set of energy
efficiency arguments can be made for freight in containers shipped via SEGway.