Evaluating Alternative Operations Strategies to Improve Travel Time ...

SHRP 2 L11: Final Report
Group
Number
Table 1.3 Classification of Freight Movers by Characteristics
Level of
Schedule
Flexibility
Level of
Operational
Adaptability
Cost of
Variability
Example company
1 Flexible Complete High
Refrigerated carrier. Carrier that operates in a very
congested arterial network. For example grocery store
deliveries by large company.
2 Flexible None High Carrier that pays drivers by the hour.
3 Inflexible Complete High
Carrier required meeting tight time windows for
delivery, for example delivery companies like Fed-Ex,
or residential moving company.
4 Inflexible None High
Carrier that moves air freight, or fresh seafood and
must deliver in tight time window.
5 Flexible Complete Low Carrier moves natural resources.
6 Flexible None Low Carrier has no delivery time windows.
7 Inflexible Complete Low Oversize/overweight specialty movers.
8 Inflexible None Low Drayage trucking company.
TRAVEL-TIME RELIABILITY REQUIREMENTS
For each of the user categories developed above, there are corresponding requirements in terms of
travel-time reliability. In order to obtain an understanding of user needs, the research team
conducted a review of literature dealing with travel-time reliability. Subsequently, surveys in the
form of focus group meetings of roadway users and stakeholders were conducted to supplement
prior work done by the research team.
Passenger Travelers
The travelers may perceive the variability in travel time in different ways depending on the context
of the trip. Thus, one may have to define measures of travel-time reliability that are appropriate for
the different types of trips. For instance, the following could serve as reliability measures for trips
classified by frequency and flexibility:
Daily, Constrained Trips: The traveler “sees” the day-to-day variability in travel time for these
trips. Further, the traveler would like to arrive at the destination at a certain time. For these trips,
reliability can be defined as the invariability in arrival time at destination from day to day.
Daily, Unconstrained Trips: The traveler “sees” the day-to-day variability in travel time, but there
is no fixed arrival-time requirement for these trips against which a measure of “schedule-delay”
can be calculated. For these trips, reliability can be defined as the invariability in travel time from
day to day.
Occasional, Constrained Trips: The traveler does not “see” the day-to-day variability as the trips
are not made daily. However, the variability affects the traveler’s ability to reach the destination on
time (This is important as these are temporarily constrained trips). For these trips, reliability can be
defined as the ability to reach the destination on time.
Occasional, Unconstrained Trips: The traveler does not “see” the day-to-day variability as the trips
are not made daily. Further, there is no fixed arrival-time requirement for these trips against which
a measure of “schedule-delay” can be calculated. However, the system reliability may affect how
long the experienced travel time is relative to the expected travel time. For these trips, reliability
can be defined in terms of how close the experienced travel time is to the expected travel time.
INTRODUCTION Page 6