Abstract
The benefit of using a PHEV comes from its ability to substitute gasoline with electricity in
operation. Defined as the proportion of distance traveled in the electric mode, the utility factor (UF)
depends mostly on the battery capacity, but also on many other factors, such as travel pattern and
recharging pattern. Conventionally, the UFs are calculated based on the daily vehicle miles traveled
(DVMT) by assuming motorists leave home in the morning with a full battery, and no charge occurs
before returning home in the evening. Such an assumption, however, ignores the impact of the
heterogeneity in both travel and charging behavior, such as going back home more than once in a day,
the impact of available charging time, and the price of gasoline. Moreover, the conventional UFs are
based on the National Household Travel Survey (NHTS) data, which are one-day travel data of each
sample vehicle. A motorist's daily distance variation is ignored. This paper employs the GPS-based
longitudinal travel data (covering 3-18 months) collected from 403 vehicles in the Seattle metropolitan
area to investigate how such travel and charging behavior affects UFs. To do this, for each vehicle, we
organized trips to a series of home and work related tours. The UFs based on the DVMT are found close
to those based on home-to-home tours. On the other hand, it is seen that the workplace charge
opportunities significantly increase UFs if the CD range is no more than 40 miles.