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CHAPTER 8
Conclusions and Suggested Research
8.1 Conclusions · Operational Constraints--practices, processes, events, or
occurrences that constrain optimal throughput, and efficient
This project developed standardized descriptions of the operating conditions. Examples include poor signal phasing,
dimensions of the freight transportation system, defined freight port gate processes, technological limitations, outdated sig-
mobility constraints in a multimodal context, developed crite- naling systems, and inadequate traveler information.
ria for low-cost and quickly implementable improvements to · Regulatory Constraints--Federal, state, or local regulatory
address freight mobility constraints, and developed a software requirements that, while intended to provide an environ-
application tool to help decision makers in evaluating freight ment for safe and secure operation, have unintended con-
mobility constraints and selecting appropriate improvements. sequences that restrict the flow of freight through the sys-
The tool is backed by a database of improvement projects for tem. Examples include safety and security requirements,
highway, rail, and deepwater ports and implemented by differ- truck restrictions, zoning policies, air quality restrictions,
ent agencies. and labor contractual limitations.
Freight mobility is constrained not only by physical infra-
structure inadequacies but also by operational, regulatory, The predominant type of freight mobility constraint (phys-
policy, technological, and financial limitations. The capac- ical, operational, or regulatory) depends on the primary mode
ity of the existing freight transportation system can be increased of freight movement. Regulatory restrictions (in particular
through innovative operational strategies, performance- Federal, state, and local land use and environmental laws and
improving regulatory and policy changes, and low-cost cap- regulations) and operational limitations (including techno-
ital improvements. logical limitations/inadequacies) are the most common types
of mobility constraints affecting all modes.
Definition of Freight Mobility Constraint
A freight mobility constraint can be defined as "a physical Criteria for Low-Cost and Quickly
or infrastructure deficiency, regulatory requirement (Federal, Implementable Improvement
state, or local), or operational action that impedes or restricts Although many innovative, low-cost efforts are being imple-
the free flow of freight either at the network level or at a spe- mented by public and private agencies, there are no unique
cific location." Mobility constraints increase costs, contribute criteria to define what constitutes a low-cost improvement
to system inefficiencies, and delay on-time freight delivery. directed to enhance freight mobility. A "low-cost and quickly
The three main types of constraints are: implementable" improvement to address freight mobility con-
straints may be defined as:
· Physical Constraints--any geometric or infrastructure con-
ditions that constrain freight operators from operating at an action that modifies existing geometry and operational
designed, safe speeds and within legally required parameters. features of the freight transportation infrastructure system and
that can be implemented within a short period without extended
Examples include inadequate capacity of the transportation
disruption to traffic flow. Such an improvement may be physical,
system to meet traffic demand (e.g., mainlines, interchanges, operational, or regulatory, as long as it enables greater through-
rail sidings, port terminals) and geometric restrictions or put from existing facilities. These actions may be spot (or location-
limitations affecting safe and efficient mobility. specific) improvements or may be limited to short sections of the
