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CHAPTER 4
Benefit-Cost Analysis
The previous chapter demonstrated from prior analyses that there are truck-only lane config-
urations that, in different types of corridors, can provide positive benefits that meet regional and
corridor planning objectives. The chapter also was able to identify some patterns in the types of
truck-only lanes that have the highest level of benefits in different scenarios, as well as the key
variables that drive benefits.
Nonetheless, there were some serious shortcomings when it comes to drawing definitive con-
clusions about the performance benefits and feasibility of truck-only lanes. Some of the most
important shortcomings included the following:
· Lack of a complete set of appropriate alternatives. The most obvious example of this prob-
lem is cases in which mitigating congestion was an objective but the study did not examine an
alternative that added capacity that was not a truck-only alternative. Congestion reduction
benefits of truck-only lanes were often based on comparison with doing nothing (no-build
alternative). Also, in some of the cases where additional mixed-flow lanes were considered in
the alternatives analysis, there were differences in capacities between the mixed-flow and
truck-only lane alternatives, due to which, the performance results were inconclusive in assess-
ing the actual benefits of truck-only lanes relative to additional mixed-flow lanes.
· Not taking into account an appropriate range of values for key variables. For example, to
the extent that diversion to LCV configurations has a direct impact on the productivity ben-
efits of LCV lanes, no studies did a market assessment for LCVs to determine which truck trips/
commodity flows would represent real candidates for diversion. In many cases, diversion sce-
narios for trucks from general purpose to truck-only lanes looked unrealistically high.
· Inability to measure all benefits with a single metric (such as monetized values) so that rel-
ative importance of benefits across types (e.g., travel time savings, reliability, and safety)
and relationships between benefits and costs can be assessed. Benefit-cost (B-C) analysis is
needed to complete the assessment of overall economic feasibility.
· Lack of important tools necessary to analyze specific truck-only lane benefits. Studies relied
heavily on traditional travel demand models and relationships between V/C ratios and other
performance measures. Tools such as traffic simulation models could have enhanced the effort
to examine actual travel times, incident-related delay, reliability, and potential safety benefits
of truck-only lanes.
· Lack of data on specific performance changes when trucks and autos are separated. Changes
in traffic flows and speeds and crash rates that are a direct function of the operational improve-
ments of separating trucks and autos were not included in any of the analysis because there is
so little field data with which to estimate these specific benefits. To the extent that data are
available, they are usually associated with auto-only lanes and not with truck-only lanes.
This section attempts to address the first three shortcomings to a limited degree through devel-
opment of a "generic corridor" analysis framework for the B-C analysis of truck-only lanes.
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