Separation of Vehicles—CMV-Only Lanes (2010) / Chapter Skim
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Pages 24-57
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From page 24... ...
. 3.2 Performance Evaluation Approach The study team's performance evaluation was based on a procedure that pulled together data reported in other studies in a way that allowed the team to compare the results of, and develop consistent performance metrics for, a variety of different truck-only lane concepts.
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Step 1. Identification of Corridor Scenarios The first step in the performance evaluation approach involved the identification of key corridor scenarios for the performance evaluation of truck-only lanes.
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Since the applicability and viability of various system improvement options is a function of corridor characteristics, the set of alternatives selected for the performance evaluation was specific to each of the two scenarios. To understand the relative performance benefits of truck-only lanes, a no-build alternative was included in all of the analyses in order to compare the performance of truck-only lanes with an alternative without truck-only lanes.
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From page 27... ...
Travel time reliability is measured by the percent change in incidentrelated (nonrecurrent) delay for the build alternatives (including the truck-only lane alternative)
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Study No-Build General Purpose Lanes with LCVs Truck Lanes with LCVs Truck Lanes without LCVs Reason Foundation Study Western Uniformity Scenario Analysis I-35 Trade Corridor Study ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ Georgia Statewide Truck Lane Needs Identification Study Table 3.2. Alternatives considered within long-haul corridor truck-only lane studies.
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The team used post-processing factors in cases where the desired performance metric was not estiPerformance Evaluation 29 Study No-Build Mixed-Flow Lanes Truck-Only Lanes TSM/TDM Strategies I-710 Major Corridor Study I-15 Comprehensive Corridor Study Georgia Statewide Truck Lane Needs Identification Study PSRC FAST Corridor Study ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ Study Travel Time Productivity Safety Reason Foundation Study Western Uniformity Scenario Analysis I-35 Trade Corridor Study Georgia Statewide Truck Lane Needs Identification Study ✓ ✓ ✓✓ ✓ ✓ ✓ Study Travel Time Reliability Safety I-710 Major Corridor Study I-15 Comprehensive Corridor Study Georgia Statewide Truck Lane Needs Identification Study PSRC FAST Corridor Study ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ Table 3.3. Alternatives considered within urban corridor truck-only lane studies.
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From page 30... ...
The handbook provides recommendations on approaches to analyze the performance benefits of truck facilities. The handbook, based on an analysis of historic accident statistics for the New Jersey Turnpike, recommends a 15% accident reduction factor due to truck-auto separation (not taking into consideration the safety benefits of capacity improvements)
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Table 3.7 presents the productivity benefits per truck estimated by the Reason Foundation study to provide insights into the following areas: • Relative productivity benefits of truck-only lanes (with and without LCV operations) compared to a no-build alternative to understand the relative contributions of travel time savings and LCV operations on truck-only lanes to productivity benefits and Performance Evaluation 31 40R.
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From page 32... ...
This is because of the assumptions in the Reason Foundation analysis, wherein it is assumed that the no-build alternative experiences significant congestion. • To quantify the relative productivity benefits of LCVs compared to standard truck operations without considering the contribution of travel time savings to productivity improvements, a comparison was made of the earnings per ton mile between the truck-only lane alternative without and with LCV operations.
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From page 33... ...
Some of the key assumptions and data gaps in this study that potentially impact the ability to gain insights and draw conclusions on the performance benefits of truck-only lanes are discussed below. • The results from this study have been included in the performance evaluation to assess the relative improvements in productivity from LCV operations compared to standard truck operations.
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Some of the key assumptions and data gaps in this study that potentially impact the ability to draw conclusions about the actual performance benefits of truckonly lanes are discussed below. • The estimates in the study on the diversion of trucks to the truck-only lanes are observed to be very optimistic, compared to the diversion rates under LCV operations derived in other studies41 (note that the study referenced is ongoing, and the results from the study on LCV diversion rates are potentially subject to change as more detailed analyses of the diversion potential 34 Separation of Vehicles -- CMV-Only Lanes 41FHWA, Technological Challenges and Policy Implications for LCVs on Exclusive Truck Facilities, I-90 Gap Closing Scenario, Draft Evaluation Results.
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From page 35... ...
• The study uses a regional travel demand model to quantify the travel time savings benefits of the truck-only lane alternative associated with speed improvements on the general purpose lanes from diversion to truck-only lanes. This approach could potentially underestimate the travel time savings benefits of the truck-only lane alternative, since travel demand models typically underestimate the congestion relief impacts of truck diversion based on their assumptions on truck PCE factors.
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From page 36... ...
• Truck-only lanes without LCVs more than double the productivity of trucking operations (in terms of increased annual trucking industry earnings) compared to the no-build alternative; • Truck-only lanes with LCV operations provide close to 7% incremental productivity benefits compared to truck-only lanes without LCV operations, due to the productivity benefits of increased payloads; and • The incremental productivity benefits due to increased payloads are observed to be significantly lower compared to the productivity benefits from travel time savings on the truck-only lanes, due to high congestion conditions on many of the intercity corridor segments, particularly those falling within the outer-limits of the Atlanta metropolitan area.
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The key data inputs used for estimating productivity benefits include speeds, freight rates, and variable costs. Speed data is derived from the Georgia study, while assumptions on freight rates and variable costs are taken from the Reason Foundation methodology for the estimation of productivity benefits.
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Travel time savings due to truck-only lanes, estimates from the Georgia study, 2035 (percentage change in VHT [millions]
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Some of the key assumptions and data gaps in this study that potentially impact the ability to draw conclusions about the performance benefits of truck-only lanes are as follow: • The study only considers the performance benefits of truck lanes compared to a no-build alternative and does not provide insights into the relative performance of truck lanes compared to adding mixed-flow capacity. This appears to be particularly relevant, since some of the corridor segments considered in the study experience significant congestion.
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The following sections summarize the key performance results from the study to gain insights into the relative performance of truck-only lanes compared to no-build and additional mixed-flow lane alternatives. Performance Results Travel Time Savings.
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IDAS post-processing factors do not consider the improvements in travel time reliability for the truck lane alternative associated with truck-auto separation. Since nonrecurrent delays are directly proportional to, and can be assumed to have a linear relationship with, the number of accidents, a 15% accident reduction factor (as recommended by the Douglas handbook)
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From page 42... ...
Combining the results from Table 3.14 and Table 3.15, Table 3.16 presents the percent improvement in safety for each of the build alternatives. For the truck-only lane alternative, an additional 15% reduction factor was applied to the total accidents to account for the safety benefits of truckauto separation (as recommended by the Douglas handbook)
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From page 43... ...
Assumptions and Data Gaps. Some of the key assumptions and data gaps in this study that potentially impact the ability to draw conclusions about the performance benefits of truck-only lanes are as follow: • The mixed-flow and truck-only lane alternatives considered in the study have different capacities.
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From page 44... ...
The average 2035 change in VHT due to the implementation of truck-only lanes, by location, is as follows: • Facility: −17%, • Corridor Buffer -- 4 mi: −11%, • Corridor Buffer -- 12 mi: −8%, and • Region: −6%. 44 Separation of Vehicles -- CMV-Only Lanes Source: Adapted from Georgia Department of Transportation, Statewide Truck Lane Needs Identification Study, Technical Memorandum 3: Truck-Only Lane Needs Analysis and Engineering Assessment, Tables 43, 52, and 51, April 2008.
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From page 45... ...
• The Travel Time Index estimates are derived from model outputs for congested and free flow travel times, and the limitations of travel demand models in assessing the mobility performance of truck-only lanes have been described earlier. Thus, the Travel Time Index estimates from the model for the truck-only lane alternative may be miscalculated, which would impact the accuracy of the Buffer Index estimates.
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The primary performance measures evaluated in the study included travel time savings in terms of change in VHT, and change in delays (congested travel time -- free-flow travel time)
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As mentioned previously, these benefits are generated in terms of percent change in VHT for each of the build alternatives compared to the nobuild alternative using VHT outputs from the FAST truck model. Figure 3.2 presents the VHT results from the alternatives analysis.
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• There is only a marginal increase in truck volumes under the build alternatives relative to the no-build alternative. The following sections summarize the key performance benefits results from the study to gain insights into the performance benefits of truck-only lanes.
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For the current analysis, these estimates were post-processed to arrive at travel time savings benefits of the build alternatives relative to the no-build alternative. The steps involved in this process include conversion of V/C estimates to average speeds along corridor segments using a volume-delay function (VDF)
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Thus, the results from the study are inconclusive in providing insights into the relative performance benefits of truck-only lanes compared to additional mixed-flow lanes. • The study, as with other studies described earlier, uses a travel demand model to evaluate the mobility performance of truck-only lanes, and based on the assumptions related to PCE factors, this process could potentially underestimate the travel time savings benefits of truck-only lanes.
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Routing decisions of the trucks are a function of travel times on the network given the O-D patterns reflected in the truck trip tables. Other benefits (such as productivity, travel time savings for users of the mixed-flow lanes, safety, and reliability)
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The general approach to estimating truck lane utilization in the studies reviewed for this performance evaluation was the use of travel demand models where routing decisions are based on minimum time or cost path assignments. This may be an appropriate method for estimating diversion of trucks to truck lanes when the primary motivation for using the truck lanes is to avoid congestion, but a more market-focused analysis is necessary when considering routing decisions for LCVs in long-haul corridors.
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From page 53... ...
• In selecting the long-haul corridor scenario, it was observed that there was a high level of interest in using truck-only lanes as a way of moving to LCV operations, thereby promoting greater freight efficiency in key freight corridors. Although the studies that were examined do show incremental benefits from LCV operations regardless of the method used to measure productivity benefits, these incremental benefits associated with LCV operations are generally small as compared with the potential benefits associated with travel time savings achieved from the Performance Evaluation 53
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From page 54... ...
compared to a no-build alternative. LCV operations provide around 6.8% incremental productivity benefits compared to standard truck operations on truck-only lanes (this is the productivity benefit associated solely with increase in payloads without considering the impacts of travel time savings on productivity improvements)
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From page 55... ...
However, neither study looked at a comparison with an alternative to build additional mixed-flow capacity. • It should be noted that the large increases in productivity benefits to trucks using the truck-only lanes (due to both travel time savings and increased payloads in the case of LCV operations)
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From page 56... ...
The results of the performance evaluation for urban corridors are summarized in Table 3.24. The key conclusions from the review of studies on the performance evaluation of truck-only lanes along urban corridors are as follow: • As mentioned in the discussion of the assumptions and data gaps associated with the reviewed literature sources, the differences in capacity assumptions between the truck-only lane and mixed-flow lane alternatives and the omission of the mixed-flow lane alternative in the performance evaluation in some of the reviewed studies result in the findings being inconclusive or inadequate in assessing the relative performance benefits of truck-only lanes against mixedflow lanes with similar capacity.
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From page 57... ...
This chapter pointed out some deficiencies in prior studies with regard to the performance evaluation of truck-only lanes for both long-haul corridors and urban corridors. Chapter 4, which follows, addresses some of these deficiencies by developing representative generic corridors for both the long-haul and urban corridor scenarios, developing an appropriate set of alternatives, monetizing the benefits so that they can be compared on a consistent basis, and evaluating these benefits in comparison to costs to get a better sense of the potential B-C tradeoffs of truck-only lanes against adding mixed-flow lane capacity.
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