Separation of Vehicles—CMV-Only Lanes (2010) / Chapter Skim
Currently Skimming:
Pages 58-77
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 58... ...
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.
|
From page 59... ...
This is particularly important when comparing LCV versus non-LCV operations on truck-only lanes since costs may be higher for LCV systems off-setting some of the productivity benefits. Yet, most of the studies reviewed for the performance evaluation task did little to assess the cost-effectiveness of truck-only lanes compared to other alternatives (such as additional mixed-flow lanes)
|
From page 60... ...
In order to recognize uncertainty in key input variables, a sensitivity analysis approach was used for the B-C analysis, which is described below. 4.1.3 Sensitivity Analysis Approach To capture some of the uncertainties involved in the range of factors driving the diversion of truck traffic to truck-only lanes (which have a direct impact on the performance benefits estimates of truck lanes)
|
From page 61... ...
This metric is typically evaluated in terms of percent savings in travel times on the general purpose lanes due to the implementation of truck-only lanes. • Reliability benefits that accrue to autos on general purpose lanes due to the implementation of truck-only lanes.
|
From page 62... ...
Since the travel time savings benefits for trucks on the truck-only lanes are captured under the productivity benefits (due to increased speeds) above, these savings are not included under the travel time savings performance measure (to avoid double-counting benefits)
|
From page 63... ...
, the cost information is presented separately for the two corridor scenarios. O&M costs are estimated based on the assumptions in the Georgia Statewide Truck Lane Needs Identification Study, which assumes O&M costs for truck-only toll lane corridors to be 0.5% of total project capital costs in the base year, which increase each year at a 3% rate of inflation (based on historic growth in CPI)
|
From page 64... ...
Truck-only lane -- with LCV 86 Incremental costs due to LCV operations derived from data presented in the Western Uniformity Scenario Analysis Mixed-flow lane N/A N/A Truck-only lane -- without LCV N/A N/A Long-Haul Corridors Construction costs -- staging areas ($ million per staging facility) Truck-only lane -- with LCV (staging area in rural location)
|
From page 65... ...
In addition to analyzing congestion reduction benefits (in terms of travel time savings) , a major feature of the analysis involves examining the benefits and costs of LCV operations on the truckonly lanes (OS/OW truck operations were not considered as part of the current analysis since there was a limited body of research available to provide inputs to allow for a robust assessment of the performance benefits of truck-only lanes with OS/OW truck operations)
|
From page 66... ...
Generally, this can be determined using standard travel demand models and commodity flow and truck O-D data. In the case of truck-only lanes with LCV operations, a more comprehensive analysis of markets that take into account the O-D patterns of the trucks, the types of commodities carried, locations of staging areas, and business characteristics of the motor carriers is required to accurately determine the diversion from standard trucks to LCVs.
|
From page 67... ...
as a function of V/C from the IDAS User Manual.46 Additionally, as discussed in the performance evaluation task, for the truck lane alternatives, the total accidents on the general purpose lanes estimated using IDAS inputs are reduced by a factor of 15%, as recommended by the Douglas handbook47 to account for the safety benefits of truck-auto separation. A more detailed discussion of the calculation methodology and results of the NPV calculation are presented in Appendix C
|
From page 68... ...
However, future analyses to assess the performance benefits of truck-only lanes should consider time-of-day variations between trucks and autos through the use of travel demand models and/or simulation tools to conduct an accurate assessment of the true performance benefits of truck-only lanes. Since none of the reviewed studies under the urban corridor scenario provide B-C analysis results based on a one-to-one comparison between truck-only lanes and additional mixed-flow lanes, the B-C assessment presented in this section is based on comparing truck-only lanes and mixed-flow lane alternatives that add the same amount of capacity.
|
From page 69... ...
relative to the no-build alternative was based on estimating average daily V/C and associated speeds on general purpose lanes and truck-only lanes given the assumptions about utilization of the truck lanes. Since this corridor scenario does not consider productivity benefits, for the truck-only lane alternative the travel time savings for trucks diverting to the truck lanes are included in the total travel time savings benefits.
|
From page 70... ...
Costs This section presents the comparative costs for all cost components of each alternative. The cost estimates are developed using the unit costs presented in an earlier section, and the configurational and travel demand characteristics along the generic corridor.
|
From page 71... ...
Productivity Travel Time Safety Total Productivity Travel Time Safety Total Productivity Travel Time Safety Total 10 – 4.9 – 4.9 0.6 0.6 0.1 1.4 1.3 0.6 0.3 2.2 20 – 4.9 – 4.9 1.2 1.1 0.3 2.6 2.6 1.1 0.5 4.2 30 – 4.9 – 4.9 1.8 1.6 0.4 3.8 3.8 1.6 0.8 6.2 40 – 4.9 – 4.9 2.4 1.9 0.5 4.9 5.1 1.9 1.1 8.1 50 – 4.9 – 4.9 3.0 2.2 0.7 5.9 6.4 2.2 1.3 9.9 60 – 4.9 – 4.9 3.6 2.4 0.8 6.8 7.7 2.4 1.6 11.7 70 – 4.9 – 4.9 4.2 2.6 0.9 7.7 9.0 2.6 1.8 13.3 80 – 4.9 – 4.9 4.8 2.7 1.0 8.5 10.2 2.7 2.0 15.0 90 – 4.9 – 4.9 5.4 2.8 1.1 9.2 11.5 2.8 2.3 16.5 100 – 4.9 – 4.9 5.9 2.8 1.2 9.9 12.8 2.8 2.5 18.0 Table 4.6. Monetized benefits of alternatives for different diversion rate assumptions, in millions of dollars (indexed to 2008)
|
From page 72... ...
, a minimum of 30% diversion would be required before the truckonly lane alternative becomes more cost-effective compared to adding mixed-flow capacity. Under the applicability of baseline conditions, the diversion rate would need to be at least 50% before truck-only lanes with LCV operations perform better compared to mixed-flow lanes.
|
From page 73... ...
. 4.7.2 Urban Corridor As in the case of the long-haul corridor scenario, the B-C analysis to evaluate the costeffectiveness of truck-only lanes compared to adding mixed-flow capacity on urban corridors was based on a sensitivity analysis approach that involved analyzing the variations in B-C ratios for the truck-only lane alternative as a function of diversion rate, and comparing these results with the benefit-cost for the additional mixed-flow lane alternative to identify the range of diversion rates for which truck-only lanes are observed to be cost-effective when compared to adding mixed-flow capacity.
|
From page 74... ...
Monetized Benefits As in the long-haul corridor scenario, a range of diversion rates is considered in the B-C analysis to assess the impact of diversion rates on the performance benefits of truck-only lanes and identify the range of diversion rates for which truck-only lanes are observed to be cost-effective when compared to adding mixed-flow capacity along urban corridors. The results for the monetized benefits under each performance measure for each alternative under different diversion rate assumptions are presented in Table 4.9.
|
From page 75... ...
used in the analysis, and uncertainties in the costs, the B-C results in Figure 4.2 are used only to assess the relative B-C performance between the mixed-flow and truck-only lane alternatives, and are not for assessing the B-C performance of each of the build alternatives individually against the no-build alternative. • The estimation of the performance benefits of alternatives does not consider differences in time-of-day distributions between auto and truck traffic volumes, which could potentially impact the benefits of truck-only lanes, and consequently, the relative B-C performance of truck-only lanes when compared to adding mixed-flow capacity.
|
From page 76... ...
These relationships are important in understanding the impacts of tolls on truck-only lanes, since higher tolls can impact diversion rates, thus affecting the benefits of truck-only lanes as well as the revenue potential of tolls. • Comparing the B-C performance of mixed-flow and truck-only lane alternatives, the mixedflow lane alternative is observed to generally have a better B-C performance when compared to the truck-only lane alternative under the defined conditions of the representative baseline corridor (although there is a range in the graph where the truck-only lane alternative could have a better performance given the uncertainties in the costs and the variations in the diversion rates)
|
From page 77... ...
For example, the results suggest that truck-only lanes could be more viable compared to mixed-flow lanes on corridors for which, in addition to congestion mitigation, there are specific performance improvement needs that could be better met by truck-auto separation than by adding mixed-flow capacity, which may include the following: Congested urban corridors on which, because of terrain such as grades and other system configurational issues, there may be safety problems due to truck-auto operational conflicts. Implementation of truck-only lanes along these corridors would provide significant levels of safety and reliability benefits in addition to travel time savings from diversion of trucks from the general purpose lanes.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.