Evaluating Alternative Operations Strategies to Improve Travel Time ...

SHRP 2 L11: Final Report
• Mode (such as single-occupant auto, multi-occupant auto, transit, and walk/bike);
• Time of Day (peak or off-peak);
• Trip Length (short, medium, long);
• Facilities Used (rural freeway, urban freeway, and arterials); and
• Weather (such as rain, snow, and clear weather).
An exhaustive classification scheme taking into account the combination of all factors identified
above would result in thousands of categories. This would be neither manageable nor useful. Thus,
the above categories are aggregated in different ways throughout the rest of this document.
Further, the intent of the above classification scheme is to facilitate the analysis of the travel-time
reliability problem in terms of (a) measures of reliability, (b) importance, (c) severity, and (d)
contributing factors. Thus, different types of aggregation are adopted that are most appropriate to
the aspect of travel-time reliability studied.
It was concluded that a broad classification, described in Table 1.1, would be useful for an analysis
of the travel-time-reliability problem of passenger travelers. Some unconstrained trips, such as
visiting friends or shopping, can have “synchronization” constraints. (Note that not all of these
trips have such constraints.) That is, they can take place within a fairly flexible time window, but
unexpected congestion or the need to account for unreliable travel times has “downstream”
implications on the traveler’s daily schedule. Consequently, these synchronization effects alter the
perceived value of time for otherwise unconstrained trips.
Table 1.1 Classification of Passenger Travelers by Trip Purpose
Broad Classification by Trip
Purpose
Daily, Constrained Trips
Daily, Unconstrained Trips
Occasional, Constrained Trips
Occasional, Unconstrained Trips
Detailed Classification by Trip
Example
Purpose
Work -
Pick-up and Drop-off Children -
Shopping
Grocery, etc.
Return-home -
Appointments
Medical, personal services, etc.
Leisure
Movies, Sports Events, etc.
Leisure
Visit Friends, etc.
Freight Movers
Freight movers can generally be classified as shippers or carriers. A shipper is an entity or business
(like Wal-Mart) that wants its goods shipped. Sometimes shippers fill their own transportation
needs but generally they contract their shipping needs to carriers. A carrier is in the business of
moving freight or goods for shippers.
The extent to which freight movers are affected by and respond to variable travel times is a
function of their operating environment. This includes the qualities of their fleet, the goods that
they carry, the environment in which they work, and the requirements of the customers that they
serve. To some extent, these are dependent. For example, a carrier that moves high-value goods
will likely have customers (shippers) that demand narrow windows for delivery. Table 1.2
classifies the freight movers by the quality of freight operations. These qualities determine how a
particular carrier will respond to, and be affected by, variable travel times.
INTRODUCTION Page 4