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30 Separation of Vehicles--CMV-Only Lanes
Table 3.6. Applicability of performance measures to scenarios.
Scenario
Performance Measure Long-Haul Corridors Urban Corridors
Travel Time
Travel Time Reliability N/A
Productivity N/A
Safety*
Note:
* There appear to be some key limitations in the evaluation methodologies and tools used to assess the safety
benefits of truck-auto separation. However, there is a body of research (described in subsequent sections) that will
allow us to consider safety impacts using post-processing techniques.
mated in a study, or where limitations were identified in the approach used by studies in the esti-
mation of specific performance metrics. Post-processing tools and sources included the following:
· Intelligent Transportation System (ITS) Deployment Analysis System (IDAS). IDAS is an
analytical tool that provides post-processing factors for the performance evaluation of trans-
portation capacity improvement strategies. Although the tool is intended to analyze the per-
formance benefits of ITS deployments, the factors can be used to assess other transportation
investments as well (such as infrastructure projects), as long as information is available on the
level of capacity improvement achieved on the transportation system. The post-processing
factors used from IDAS for the performance evaluation included the following:
Accident rates (number of accidents per million VMT) by type of accident for autos and
trucks as a function of V/C38 ratio, for the estimation of safety benefits (reduction in
accidents); and
Incident delay rates (hours of incident-delay per vehicle mile) as a function of V/C and num-
ber of lanes, for the estimation of reliability benefits (savings in incident-related delay).
· Handbook for Planning Truck Facilities on Urban Highways39 (Douglas handbook) and New
Jersey Turnpike Accident Data. The Douglas handbook serves as a compendium of key issues
related to the planning, policy, and performance/feasibility evaluation of truck facilities. 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 Jer-
sey Turnpike, recommends a 15% accident reduction factor due to truck-auto separation (not
taking into consideration the safety benefits of capacity improvements). This 15% accident
reduction factor is used in the study team's analysis. (A summary of historic accident statistics
on the dual-dual and non dual-dual sections of the New Jersey Turnpike and the basis for arriv-
ing at a 15% accident reduction factor to account for the safety benefits of truck-auto separation
is provided in Appendix B, Section B.3, which is available on the TRB website at www.TRB.org
by searching for NCHRP Report 649/NCFRP Report 3).
3.3 Performance Evaluation Results
The following sections provide a brief overview of each of the major truck-only lane studies iden-
tified in Step 4, discuss important findings within the four key performance metrics identified in
Step 3 (Selection of Performance Measures and Metrics), and identify key assumptions and data
38
V/C is a parameter used to quantify the level of congestion on a roadway. It is calculated as the ratio of the
level of demand (traffic volume) to the supply (capacity of roadway). Typically, V/Cs are measured for a
specific time period (e.g., hourly or daily).
39
J. G. Douglas, Handbook for Planning Truck Facilities on Urban Highways, August 2004. This reference was
used primarily to estimate safety benefits consistently.
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Performance Evaluation 31
Table 3.7. Reason Foundation study's truck-only lane productivity benefits.
Mixed Truckway
Freeway Truckway Truckway Turnpike
Semitrailers Semitrailer Triple Short Double
Payload (Pounds) 45,000 45,000 67,500 90,000
Metric Tons 20 20 30 40
100-mi Delivery (2004 Freight Rates) $500 $500 $750 $1,000
Average Speed on the Road 38 mph 60 mph 60 mph 60 mph
Miles Driven in 8-h Shift 228 360 360 360
Revenue from 6-h Payload at 2004 Rates $1,140 $1,800 $2,700 $3,600
Variable Costs $684 $684 $1,007 $1,165
Earnings (Revenue--Costs) $456 $1,116 $1,693 $2,435
Earnings (per Ton-Mile) $0.100 $0.155 $0.157 $0.169
Productivity Benefit (% Increase in
Earnings per Ton-Mile) (Truck Lanes 55% 63%
Compared to Mixed-Flow Lanes)
Productivity Benefit (% Increase in
Earnings per Ton-Mile) (Truck Lanes
5%
with LCVs Compared to Truck Lanes
without LCVs)
Source: Adapted from Poole, Jr., R. W., and P. Samuel, Toll Truckways: Increasing Productivity and Safety in
Goods Movement, Reason Foundation, 2005,
http://www.fhwa.dot.gov/download/hep/freightplanning/talkingfreight3_16_05bp.ppt.
gaps that hindered the study team's ability to draw specific conclusions from each of these scenar-
ios. A more detailed discussion and summary of each of these studies is provided in Appendix B
(Sections B.1 and B.2, which are available on the TRB website at www.TRB.org by searching for
NCHRP Report 649/NCFRP Report 3).
3.3.1 Long-Haul Corridors
The following sections present the results of the performance evaluation of truck-only lanes
along long-haul corridors, based on a detailed review of studies listed in Step 4.
Reason Foundation Study
The Reason Foundation conducted an analysis40 of toll truckways that compared the incremen-
tal productivity benefits of three types of truck-only lanes to mixed-flow facilities without LCV
operations (the no-build scenario). In addition to a "standard" semi-trailer option (i.e., 80,000-lb,
53-ft trailers), two LCV options were evaluated--one allowing triple shorts and one allowing turn-
pike doubles. The Reason Foundation study is useful in presenting an illustrative methodological
framework for the analysis of productivity benefits and for providing estimates to determine the
relationship between speed improvements and LCV operations, as well as productivity benefits
measured in terms of increased earnings per truck per ton mile. Table 3.7 presents the produc-
tivity 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
40
R. W. Poole, Jr. and P. Samuel, Toll Truckways: Increasing Productivity and Safety in Goods Movement, Rea-
son Foundation, http://www.fhwa.dot.gov/download/hep/freightplanning/talkingfreight3_16_05bp.ppt.
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32 Separation of Vehicles--CMV-Only Lanes
· Incremental productivity benefits to trucks from LCV operations on truck-only lanes compared
to standard truck operations on truck-only lanes (this provides insights into the productivity
benefits associated with increased payloads alone, without taking into consideration the produc-
tivity benefits from travel time savings).
Performance Results
Productivity Benefits. As shown in Table 3.7, the productivity benefits of truckways can be
attributed to travel time savings, as well as increased payloads from LCV operations. Assuming
an equal split of triple-short and turnpike double trucks under the truck-only lanes with the LCV
operations alternative, some of the key findings from the Reason Foundation analysis results on
productivity benefits are summarized below.
· A large share of the productivity benefits of truck-only lanes are observed to be associated with
travel time savings (55% increase in earnings per ton mile from travel time savings compared
to 63% from LCV operations, which include the benefits from travel time savings). Thus, the
incremental benefits to trucking productivity from LCV operations are observed to be small
compared to the benefits from travel time savings. 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 with-
out and with LCV operations. The study team observed that LCV operations provide only a 5%
increase in earnings per ton mile compared to standard truck operations on truck-only lanes.
Travel Time Improvements. The study did not analyze travel time savings.
Safety Improvements. The study did not analyze safety benefits.
Assumptions and Data Gaps. Some of the key assumptions and data gaps in the Reason
Foundation approach that potentially impact the ability to draw conclusions about the actual
performance benefits of truck-only lanes are as follow:
· The productivity benefits from the study are based on arbitrary assumptions regarding the con-
gestion conditions in the no-build and truckway alternatives. The study assumes a very high
average level of congestion in the no-build alternative. As a result, a large share of the produc-
tivity benefits accrue from travel time savings compared to the benefits from increase in payload.
Due to this assumption, the results from the study could potentially be inconclusive in provid-
ing insights into the incremental productivity benefits of LCV operations on long-haul corri-
dors, particularly among corridors with low congestion levels.
· The study does not provide any insights into the diversion potential of truck-only lanes (due to
their performance benefits), and only provides estimates for productivity benefits per truck.
Thus, the study, although providing a useful analytical framework for the evaluation of produc-
tivity benefits of truck-only lanes, can not be used to assess the total productivity benefits of
implementing truck-only lanes along a corridor (since these benefits are inherently tied to the
total trucks that divert to the truck-only lanes).
Western Uniformity Scenario Analysis
The Western Uniformity Scenario Analysis, conducted by U.S.DOT in 2004, analyzed the impacts
of lifting the LCV freeze and allowing uniformity in LCV operations (weights and dimensions)
among western states with current LCV operations based on a key set of performance criteria,
including safety, pavement, bridge and infrastructure costs, shipper costs, energy consumption,
environmental quality, and traffic operations. To understand the productivity benefits of LCVs
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Performance Evaluation 33
Table 3.8. Annual shipper cost savings from Western Uniformity
Scenario Analysis.
Amount Percentage
Source of Savings (Millions of 2000 Dollars) of Change
Truck to Truck Diversion 2,036 3.9%
Rail to Truck Diversion 3 .01%
Rail Discounts 26 .11%
Total 2,065 n/a
Source: Reprinted from U.S.DOT, Western Uniformity Scenario Analysis: A Regional Truck Size and Weight
Scenario Requested by the Western Governors' Association, April 2004,
http://www.fhwa.dot.gov/policy/otps/truck/wusr/wusr.pdf.
compared to standard truck operations on general purpose lanes, this section presents the results
from the study on shipper cost savings from uniform LCV operations.
The study estimated total annual shipper cost savings resulting from uniform LCV operations
in western states of around $2 billion per year, as shown in Table 3.8. The vast majority of these
savings would accrue to shippers diverting shipments from standard trucks to LCVs, with minor
benefits resulting from rail to LCV diversions and more competitive rail rates provided to shippers.
Performance Results
Productivity Improvements. According to the study, the implementation of LCV operations
on existing facilities (to achieve uniformity in LCV operations in all the western states considered
in the analysis) will result in total productivity benefits (in terms of shipper cost savings) of close
to 4% (around $2 billion annually) compared to the no-build scenario. These benefits are associ-
ated with reduced operating costs to the trucking industry from shifting to LCV operations.
Travel Time Improvements. The study did not analyze travel time savings benefits due to
LCV operations on mixed-flow lanes.
Safety Improvements. The study, although providing a comprehensive comparative discus-
sion of accident rates associated with LCVs and non-LCVs, does not quantify the safety benefits
of the LCV uniformity alternative compared to the base case (no-build).
Assumptions and Data Gaps. 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 rel-
ative improvements in productivity from LCV operations compared to standard truck opera-
tions. Since the two alternatives in the study do not involve any system capacity improvements,
the results provide insights into the productivity benefits solely associated with increased pay-
loads from LCV operations.
· The study quantifies productivity benefits of LCV operations in terms of shipper cost savings,
while the total productivity benefits accruing to the trucking industry (in terms of increased
earnings from LCV operations, for example) are not reported. Since shipper cost savings only
account for a share of the total productivity benefits, the results from the study only provide
the lower threshold of the total productivity benefits of LCV operations.
· Since the study does not consider CMV-only lanes as part of the LCV uniformity scenario,
results from the study cannot be used to assess the performance benefits of truck-only lanes
with LCV operations.
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34 Separation of Vehicles--CMV-Only Lanes
· The study assumes close to 50% diversion of tractor-semi-trailer shipments to LCVs for the
LCV scenario, but there is inadequate explanation of the rationale and data to support this
assumption. Also, since this assumption is for an LCV uniformity scenario that does not
include truck-only lanes, this assumption is expected to not be applicable to a truck-only lane
alternative with LCV operations.
I-35 Trade Corridor Study
Completed in 1999, the I-35 Trade Corridor Study evaluated a set of alternatives with the
objective of arriving at recommended corridor investment strategies to improve local, intrastate,
interstate, and international service along the I-35 corridor between Laredo, Texas, and Duluth,
Minnesota, in the future (2025). The results from the study provide some useful insights into the
performance benefits of truck-only lanes along long-haul corridors, compared to alternative
investment strategies. The primary performance criteria evaluated in the study included savings
in vehicle operating costs, travel time savings, and safety benefits.
Performance Results
Productivity Improvements. The study quantified the productivity benefits of the truck-only
lane alternative in terms of reduction in truck operating costs. The study estimated that the truck-
only lane alternative will provide around 36% savings in truck operating costs compared to the no-
build alternative. These savings result from increased travel speeds as well as increased payloads
from LCV operations on the truck-only lanes.
Travel Time Improvements. Travel time savings estimates for the various alternatives were
derived using the regional travel demand model, which employs volume-delay functions (VDF) to
generate vehicle speeds (and travel times) as a function of congestion parameters such as V/C. The
study estimated that the truck-only lane alternative provides around 21% savings in travel time
compared to the no-build alternative.
Safety Improvements. Since the I-35 study did not estimate percent reductions in acci-
dents associated with truck-only lanes, an attempt was made to quantify the approximate percent
improvement in safety, based on the estimation of percent reduction in passenger car equivalents
(PCEs), assuming a PCE factor of 2.0 for trucks, on the general purpose lanes. The percent change
in congestion (V/C) along the corridor for the truck-only lane alternative (relative to the alter-
native without truck-only lanes) was assumed to be the same as the percent change in PCEs, since
the general purpose lane capacity along the corridor does not change under the two alternatives,
and safety benefits are directly proportional to change in corridor congestion. Results from the
study indicate an average safety improvement of 38% along the corridor due to truck-only lanes.
Since these benefits are solely associated with congestion reduction and do not include the safety
benefits of truck-auto separation, an additional accident reduction factor of 15% (as recommended
by the Douglas handbook) was applied to the results, providing a total percent reduction in acci-
dents for the CMV-only lane alternative of around 47% compared to the no build alternative.
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 actual performance benefits of truck-
only 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 diver-
sion rates are potentially subject to change as more detailed analyses of the diversion potential
41
FHWA, Technological Challenges and Policy Implications for LCVs on Exclusive Truck Facilities, I-90 Gap Clos-
ing Scenario, Draft Evaluation Results.
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Performance Evaluation 35
of LCV operations are conducted). The study estimated that the trucks on the truck-only lanes
(adjusted for LCVs) accounted for 79% of total trucks. This implies that the assumption in the
study on the actual diversion of trucks to the truck-only lanes would be greater than 79%, since
the adjustment for LCVs would result in a net reduction of total truck volumes on the truck-
only lanes. Although part of this diversion would be driven by congestion relief considerations,
the diversion would also be impacted by productivity improvements offered by LCV operations,
the propensity of the trucking market (type of commodities and origination-destination [O-D]
patterns) toward shifting to LCVs, and other LCV operational considerations (e.g., equipment
and operational costs). It is unclear if these issues associated with LCVs were considered in the
study in arriving at the diversion rates (and corresponding utilization of the truck-only lanes).
Since the performance benefits of the truck-only lane alternative are directly linked with the
assumptions on the level of diversion of trucks from the general purpose lanes, it is difficult to
draw conclusions from the results of this study on the performance benefits of truck-only lanes
without adequate information on the inherent factors driving these diversion estimates.
· 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 assump-
tions on truck PCE factors.
· The alternatives defined in the study prevented the ability to compare the performance benefits
of the truck-only lane alternative against an alternative with additional mixed-flow capacity
(Appendix B provides a detailed description of the alternatives considered in this study.).
· The study does not consider the impacts of differences in time-of-day distributions between
trucks and autos on the utilization and associated performance benefits of the truck-only lane
alternative, which could potentially impact the results reported in the study on the relative per-
formance benefits of the truck-only lanes.
Georgia Statewide Truck Lane Needs Identification Study
The Georgia Statewide Truck Lane Needs Identification Study (i.e., the Georgia study) was con-
ducted to evaluate the feasibility of implementing truck-only lanes on Georgia's statewide highway
network. The main objectives of the study included quantifying the performance benefits of truck-
only lanes (relative to an alternative without truck-only lanes), identifying potential corridors for
implementation (based on certain feasibility criteria such as truck volumes, congestion, and mar-
ket accessibility), and assessing the benefits and costs of implementing truck-only lanes. The hori-
zon year for the study was 2035.
The initial phase of the study considered all the major Interstate facilities and access controlled
state routes in Georgia for the truck-only lane needs identification analysis. An initial screening
process (based on a qualitative performance evaluation process) was undertaken to evaluate the
feasibility of truck-only lanes along these corridors, which resulted in the identification of a set of
"candidate corridors" showing the greatest potential for the implementation of truck-only lanes to
meet the freight and transportation needs in the state. The candidate long-haul corridors identi-
fied in the study to have the greatest potential for truck-only lanes included the following:
· I-75 (southern segment) between I-285 (south end) and I-475 (near Macon). This segment
was divided into the following subsegments:
Segment 3A: Henry/Butts County line to I-285 and
Segment 3B: I-475 to Henry/Butts County line.
· I-75 (northern segment) between I-285 (north end) and Georgia/Tennessee boundary. This
segment was divided into the following subsegments:
Segment 4A: I-285 to Bartow/Gordon County line and
Segment 4B: Bartow/Gordon to Tennessee.
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36 Separation of Vehicles--CMV-Only Lanes
· I-85 (southern segment) between I-285 and Georgia/Alabama boundary. This segment was
divided into the following subsegments:
Segment 6A: Alabama to Coweta/Troup County line and
Segment 6B: Coweta/Troup County line to I-285.
· I-85 (northern segment) between I-285 and Georgia/South Carolina boundary. This segment
was divided into the following subsegments:
Segment 7A: I-285 to Gwinnett/Jackson County line and
Segment 7B: Gwinnett/Jackson County line to South Carolina.
· Segment 8: I-20 (western segment) between I-285 and Georgia/Alabama boundary.
· Segment 9: I-20 (eastern segment) between I-285 and Georgia/South Carolina boundary.
Appendix B provides a detailed description of the candidate corridors, auto and truck traffic
demand along these corridors and how these were generated, and the performance benefits esti-
mates for the alternatives considered in the study.
Performance Results
Productivity Benefits. The study did not look at productivity benefits as an exclusive perfor-
mance metric in evaluating the performance benefits of truck-only lanes. Therefore, productivity
benefits were derived using a post-processing analysis based on the Reason Foundation approach
to estimating productivity benefits of truck-only lanes presented in Table 3.7. This post-processing
analysis used the speeds from the Georgia study as inputs along with other assumptions on freight
rates and truck variable costs (consistent with the assumptions used by the Reason Foundation and
presented in Table 3.7), to derive the relative increase in trucking industry earnings due to truck-
only lanes. Table 3.9 presents the productivity benefits to truckers for a select set of corridor seg-
ments (Segments 3B, 4A, 4B, 6B, and 7A) due to usage of truck-only lanes (without and with LCV
operations) compared to the no-build alternative.
Although the study did not consider LCV operations, the post-processing analysis also consid-
ered a truck-only lane alternative with LCV operations, to assess the incremental productivity ben-
efits of truck-only lanes with LCV operations (due to increased payloads). The productivity benefits
results are summarized below.
· 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.
Travel Time Improvements. Travel time savings of truck lanes are estimated as the savings in
vehicle hours traveled (VHT) between the no-build and the truck-only lane alternatives. Total VHT
for autos and trucks are derived for the study alternatives using travel demand models for each of
the candidate corridor segments, and these results are presented in Table 3.10. VHT savings are
considered to be representative of travel time savings under the assumption that traffic volumes do
not change significantly between the no-build and the truck-only lane alternatives. Truck lanes
along the intercity corridors considered in the study are estimated to provide 20% savings in travel
time compared to the no-build alternative.
Safety Improvements. Safety performance evaluation of alternatives was conducted in terms
of change in the number of fatal accidents, using crash rate data from the Georgia DOT, as a func-
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Table 3.9. Productivity benefits estimates of truck-only lanes using the Reason Foundation methodology
applied to data from the Georgia study,1 2035.
Segment 3B: Segment 4A: Segment 4B: Segment 6B: Segment 7A:
I-75 South I-75 North I-75 North I-85 South I-85 North
Without Without No Without No Without No Without No
2 3 4
TOL No LCV LCV TOL LCV LCV TOL LCV LCV TOL LCV LCV TOL LCV LCV
Speeds (mph) 61 64 64 27 52 52 56 62 62 38 57 57 29 51 51
Freight Rate (per 100 mi) 500 500 875 500 500 875 500 500 875 500 500 875 500 500 875
Miles per 8-h Day Shift 366 384 384 162 312 312 336 372 372 228 342 342 174 306 306
(6 h Driving)
Revenue per Day Shift 1,830 1,920 3,360 810 1,560 2,730 1,680 1,860 3,255 1,140 1,710 2,993 870 1,530 2,678
Variable Costs 684 684 1,086 684 684 1,086 684 684 1,086 684 684 1,086 684 684 1,086
Net Earnings 1,146 1,236 2,274 126 876 1,644 996 1,176 2,169 456 1,026 1,907 186 846 1,592
Earnings per Ton Mile 0.16 0.16 0.17 0.04 0.14 0.15 0.15 0.16 0.17 0.1 0.15 0.16 0.05 0.14 0.15
% Increase in Earnings 3 8 261 287 7 12 50 59 159 178
per Ton Mile
Source: Cambridge Systematics, Inc. (based on the Reason Foundation approach and data inputs from the Georgia study).
Notes:
1. Productivity benefits of truck-only lanes are estimated separately in the table for each of the major corridor segments in the Georgia study. The corridor segments
in the table include 3B, 4A, 4B, 6B, and 7A. 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.
2. Refers to the no-build alternative (without truck-only lanes [TOL]).
3. Refers to the truck-only lane alternative with standard truck (no LCV) operations.
4. Refers to the truck-only lane alternative with LCV operations.
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Table 3.10. Travel time savings due to truck-only lanes, estimates from the Georgia study, 2035
(percentage change in VHT [millions]).
Without Truck-Only Lanes With Truck-Only Lanes % Travel Time Savings1
Corridor 4-Mile 12-Mile 4-Mile 12-Mile 4-Mile 12-Mile
Segments Facility 2 Buffer 3 Buffer 4 Region5 Facility Buffer Buffer Region Facility Buffer Buffer Region
3A: I-75 South 0.3 1.0 2.6 10.3 0.2 0.8 2.5 10.1 42 15 7 2
3B: I-75 South 0.1 N/A N/A 38.1 0.1 N/A N/A 38.1 0 N/A N/A 0
4A: I-75 North 0.3 1.1 3.3 10.3 0.2 1.0 3.1 10.0 23 11 5 2
4B: I-75 North 0.1 N/A N/A 38.1 0.1 N/A N/A 38.1 8 N/A N/A 0
6B: I-85 South 0.1 0.5 1.9 10.3 0.1 0.5 1.8 10.3 9 6 1 0
7A: I-85 North 0.2 1.1 3.7 10.3 0.2 1.0 3.6 10.1 11 5 3 1
8: I-20 West 0.2 0.7 2.5 10.3 0.1 0.6 2.8 10.2 20 8 -15 1
9: I-20 East 0.1 0.6 2.6 10.3 0.1 0.6 2.6 10.2 13 2 1 0
Total VHT 1.2 4.9 16.5 137.7 1.0 4.5 16.4 137.0 20 9 1 0
and Average
Savings
Source: Adapted from Georgia Department of Transportation, Statewide Truck Lane Needs Identification Study, Technical Memorandum 3: Truck-Only Lane
Needs Analysis and Engineering Assessment, April 2008.
1. Percent savings in travel time are calculated as the percent reduction in VHT between the "with truck-only lanes" and "without truck-only lanes" alternatives.
2. The cells in this column represent daily VHT (in millions) for users on each of the Interstate corridor segments.
3. The cells in this column represent daily VHT (in millions) for users traveling on roadways within a 4-mi buffer area on either side of each of the Interstate corridor segments.
4. The cells in this column represent daily VHT (in millions) for users traveling on roadways within a 12-mi buffer area on either side of each of the Interstate corridor segments.
5. The cells in this column represent daily VHT for users on the entire roadway network (within the study area).
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Performance Evaluation 39
Table 3.11. Safety benefits due to truck-only lanes, 2035
(fatal accident reduction).
Estimated Annual Fatal Accidents
15% Additional Percentage
Adjustment for of Savings
Corridor Without TOL With TOL TOL in Accidents
3A: I-75 South 11 7 6 46%
3B: I-75 South 10 7 6 41%
4A: I-75 North 14 9 8 45%
4B: I-75 North 10 7 6 41%
6B: I-85 South 9 6 5 43%
7A: I-85 North 10 7 6 41%
8: I-20 West 10 6 5 49%
9: I-20 East 8 5 4 47%
Total Fatal Accidents and Average % 82 54 46 44%
Savings
Source: Adapted from Georgia Department of Transportation, Statewide Truck Lane Needs Identification Study,
Technical Memorandum 3: Truck-Only Lane Needs Analysis and Engineering Assessment, April 2008.
tion of roadway facility type and congestion. Clearly, the method used for accident estimation in
the study did not consider the incremental safety benefits associated with truck-auto separation.
As a result, additional post-processing was conducted to account for the safety benefits of truck-
auto separation, by applying an additional 15% accident reduction factor (as recommended by the
Douglas handbook). Table 3.11 presents the safety benefits estimates from the study. Truck lanes
along the intercity corridor segments considered in the study are estimated to reduce accidents by
44% compared to the no-build alternative, as a result of congestion reduction as well as separation
of trucks and autos.
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 study only considers the performance benefits of truck lanes compared to a no-build alter-
native 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.
· The study uses travel demand models to estimate the travel time savings benefits of truck lanes
compared to the no-build alternative. Since trucks account for a large share of total traffic vol-
umes along most of the corridor segments (close to 40% on average), the estimation of the con-
gestion relief benefits of eliminating trucks from the general purpose lanes has to accurately
consider the congestion impacts of trucks (when trucks represent a large share of the total traf-
fic volumes) through the use of representative PCE factors. Typically, this is a limitation with
travel demand models, which do not consider variable PCEs. Consequently, the results from the
study could be underestimating the travel time savings of truck lanes, particularly along the con-
gested corridor segments.
· The safety benefits results from the study are based on the congestion reduction benefits of truck
lanes, and the safety benefits of truck-auto separation are accounted for by applying an addi-
tional accident reduction factor as part of a post-processing analysis. Clearly, the safety benefits
estimates are not based on robust analytical tools (such as simulation) that can capture the true
safety benefits of truck-auto separation.
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40 Separation of Vehicles--CMV-Only Lanes
· The study does not consider differences in time-of-day distributions between trucks and autos,
which could impact the performance of truck-only lanes.
3.3.2 Urban Corridors
I-710 Major Corridor Study
The I-710 Major Corridor Study was initiated in 2001 to analyze future year traffic volumes, con-
gestion, safety, and environmental issues along the I-710 corridor in Southern California, with the
objective of developing transportation solutions to address these issues. Traffic forecasts along
the corridor for each of the alternatives were generated using a subarea travel demand model for
the I-710 study area. These forecasts served as inputs in the estimation of key performance mea-
sures, including V/Cs, speeds, travel times, and number of accidents. The following sections
describe the results from the study related to travel time savings, reliability, and safety.
Additional post-processing was conducted to estimate reliability (since the study did not esti-
mate these benefits), and safety (this was done for the truck-only lane alternative since the study
did not specifically account for the safety benefits of truck-auto separation). Appendix B provides
a detailed description of the alternatives, performance measures considered, and performance ben-
efits results from the study for each of the alternatives. 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. The study evaluated mobility performance among alternatives in terms
of speeds on general purpose lanes (and speeds on truck lanes in the case of the truck-only lane
alternative) for each of the alternatives that were derived using a subarea travel demand model.
These speeds were translated into equivalent travel time savings as part of a post-processing analy-
sis. The relative savings in travel time for the build alternatives compared to the no-build alterna-
tive are presented in Table 3.12.
Following are some insights into the travel time savings benefits of truck-only lanes estimated
in the study:
· For the truck-only lane alternative, the travel time savings for trucks using the truck-only lanes
are significantly higher (more than double) than the savings for autos and trucks on the general
Table 3.12. Percent travel time savings compared to no build, 2025
(northbound lanes, P.M. peak period).
General Purpose Truck/Carpool
Alternatives Lanes Lanes
TSM/TDM1 8% N/A
Mixed-Flow Lanes (One Lane in Each Direction) 14% N/A
Mixed-Flow Lanes (Two Lanes in Each Direction) with 21% 37%
Additional HOV Lanes2
Truck-Only Lanes 16% 33%
Source: Adapted from Los Angeles County MTA, I-710 Major Corridor Study--Final Report, March 2005.
Notes:
1. Includes improvement strategies such as added bus service for local area communities, ramp metering system on
I-710, advanced technologies for traffic management, and motorist information systems for route choice decision
making based on traffic congestion.
2. Four additional bidirectional lanes between SR 91 and SR 60 and six additional bidirectional lanes between
Ocean and SR 91.
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Performance Evaluation 41
purpose lanes. This is because of the lower level of congestion on the truck-only lanes compared
to the congestion relief provided on the general purpose lanes due to truck diversion.
· The relative travel time savings benefits on the general purpose lanes between the truck-only lane
and mixed-flow lane (one lane in each direction) alternatives are observed to be not that signif-
icant, even though the truck-lane alternative has higher capacity. This could be attributed to the
lower level of contribution of trucks to congestion in the P.M. peak period.
Reliability Benefits. The I-710 study did not estimate the reliability benefits associated with
each of the build alternatives. In order to estimate percentage change in reliability for each of the
build alternatives compared to the no-build, the study team used a post-processing approach. This
approach involves estimating total nonrecurrent/incident-related delays for each of the alter-
natives, and comparing these estimates for the build alternatives against the no-build alternative
to arrive at percent change in incident-related delays.
Total nonrecurrent delay per vehicle mile is estimated using post-processing factors as a func-
tion of V/C and number of lanes. The approach involves estimating nonrecurrent delay per vehi-
cle mile for various sections of the I-710 corridor based on information on V/C and number of
lanes from the I-710 Major Corridor Study. The nonrecurrent delay estimates per vehicle mile are
then averaged out for the corridor, and multiplied by the total VMT along the corridor (from the
I-710 Major Corridor Study) for each of the alternatives.
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) is applied to the non-
recurrent delay estimates for the truck-only lane alternative from the I-710 study. The final esti-
mates for percentage change in reliability for the build alternatives in the I-710 study compared to
the no-build alternative are presented in Table 3.13.
The percentage change in reliability for the truck lane alternative in Table 3.13 includes relia-
bility improvements both on the GP and truck lanes. Since reliability improvements on the truck
lanes are expected to be significantly higher than those for the GP lanes (as was observed from the
Georgia study), the reliability improvements on the GP lanes for the truck-only lane alternative
are expected to be lower than the 59% figure for the truck-only lanes.
Safety Benefits. The I-710 study analyzed safety benefits among alternatives in terms of reduc-
tion in accidents under each of the build alternatives compared to the no-build alternative. These
results are presented in Table 3.14.
In order to determine percent improvements in safety relative to the no-build alternative, addi-
tional post-processing of the results from the I-710 study was conducted, using IDAS safety factors
Table 3.13. Percent change in travel time reliability.
Total Annual Savings in Percentage of Reliability
Alternatives Nonrecurrent Delay (Hours) Improvement
A. No Build
B. TSM/TDM 2,375 15%
C. Mixed-Flow Lanes (One Lane in Each 7,403 47%
Direction)
D. Mixed-Flow Lanes (Two Lanes in Each 9,935 63%
Direction) with Additional HOV Lanes
E. Truck-Only Lanes 9,308 59%
Source: Adapted from Los Angeles County MTA, I-710 Major Corridor Study--Final Report, March 2005.
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42 Separation of Vehicles--CMV-Only Lanes
Table 3.14. Annual accident
reduction (2025).
Alternatives Reduction in Accidents*
B 316
C 554
D 480
E 539
* When compared to Alternative A.
Source: Adapted from Los Angeles County MTA, I-710 Major
Corridor Study--Final Report, March 2005.
as a function of V/C, to determine annual accidents under the no-build alternative. The approach
and results from this post-processing are shown in Table 3.15.
Combining the results from Table 3.14 and Table 3.15, Table 3.16 presents the percent improve-
ment 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 truck-
auto separation (as recommended by the Douglas handbook).
Table 3.15. Annual accidents under the no-build alternative, 2025.
V/C 1.42
Daily VMT 4,400,000
Fatality Rate (Accidents per Million VMT) 0.0066
Injury Rate (Accidents per Million VMT) 0.71
Property Damage Rate (Accidents per Million VMT) 0.9192
Daily Fatality Accidents 0
Daily Injury Accidents 3
Daily Property Damage Accidents 4
Total Daily Accidents 7
Total Annual Accidents (Assuming a Factor of 300) 2,159
Source: Adapted from Los Angeles County MTA, I-710 Major Corridor Study--Final Report, March 2005.
Table 3.16. Percent safety improvement, 2025.
Additional
Reduction Due Percentage of
Annual to Truck-Auto Net Annual Accident
Alternatives Accidents Separation Accidents Reduction
No Build 2,159 N/A 2,159
TSM/TDM 1,843 N/A 1,843 15%
Mixed-Flow Lanes (One Lane in 1,605 N/A 1,605 26%
Each Direction)
Mixed-Flow Lanes (Two Lanes 1,679 N/A 1,679 22%
in Each Direction) with
Additional HOV Lanes
Truck-Only Lanes 1,620 243 1,377 36%
Source: Adapted from Los Angeles County MTA, I-710 Major Corridor Study--Final Report, March 2005.
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Performance Evaluation 43
Some key insights from the performance benefits results from the I-710 study are as follow
(potential limitations associated with these results are discussed in the next section):
· The study provides insights into the relative performance of truck-only lanes compared to
no-build and additional mixed-flow lane alternatives for travel time savings, reliability, and
safety performance measures;
· Relative improvements in reliability and safety benefits of truck-only lanes (compared to
additional mixed-flow lanes) are observed to be higher compared to travel time savings
because, in addition to congestion relief (which contributes to reliability and safety improve-
ments), the separation of trucks and autos in the truck-only lane alternative also provides
incremental reliability and safety benefits; and
· The truck-only lane alternative provides the highest safety benefits compared to all other
alternatives.
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 capac-
ities. Therefore, without a B-C analysis, it is difficult to assess, from the results, the relative over-
all performance of truck-only lanes compared to adding mixed-flow capacity.
· The travel time savings benefits are calculated using the speed outputs from a subarea travel
demand model. As discussed earlier, the applications of travel demand models to analyze the
mobility performance of truck-only lanes have potential limitations, especially in congested
corridor conditions (such as in the case of the I-710 corridor), particularly regarding assump-
tions related to truck PCE factors, which could result in an underestimation of the actual travel
time savings benefits of truck-only lanes.
· The study provides mobility performance results for the build alternatives in terms of average
speeds for the P.M. peak period, which are translated into travel time savings benefits as part of
a post-processing analysis. However, travel time savings for only the P.M. peak period are inad-
equate in assessing the performance of truck-only lanes since differences in time-of-day patterns
of trucks in the A.M. peak and mid-day time periods could potentially affect the performance of
the truck-only lane alternative relative to adding mixed-flow capacity.
Georgia Statewide Truck Lane Needs Identification Study
The Georgia Statewide Truck Lane Needs Identification Study used a two-pronged approach in
the performance evaluation and needs analysis process for truck-only lanes. The first step in the
process involved the analysis of individual corridor segments and the quantification of perfor-
mance benefits of truck lanes on these corridors. The results from this analysis for the long-haul
corridors in the state were discussed previously in the long-haul corridor performance evaluation
section. The second step involved the development of truck-only lane systems (combination of
individual corridors) and a detailed evaluation of the performance benefits of truck-only lane sys-
tems compared to a system without truck-only lanes.
The performance measures evaluated in the study for the analysis of truck-only lanes along the
above-mentioned corridor systems included travel time savings, reliability, and safety benefits.
The study used a combination of the Georgia statewide model, the Atlanta Regional Commission
(ARC) travel demand model, and the Savannah Metropolitan Planning Organization (MPO)
model to generate traffic forecasts on the corridor systems, and estimate travel time and reliabil-
ity performance measures for each alternative. Safety performance was analyzed using crash rates
available from GDOT, in terms of number of accidents using V/C and VMT outputs from the
model. Appendix B provides a detailed description of the metropolitan corridor systems, alterna-
tives, and performance measures considered in the study. The following sections present the key
performance benefits results from the study to gain insights into the relative performance of truck-
only lanes compared to the no-build alternative.
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44 Separation of Vehicles--CMV-Only Lanes
Performance Results
Travel Time Savings. Travel time savings due to truck-only lanes were evaluated in terms of
changes in VHT in 2035 for each of the corridor systems. Analysis of change in VHT to evaluate
travel time savings provides a conservative estimate for travel time savings, because part of the
VHT change is contributed by increase in traffic volumes on the corridor due to increased capac-
ity. Table 3.17 summarizes these results. The average 2035 change in VHT due to the implemen-
tation of truck-only lanes, by location, is as follows:
· Facility: -17%,
· Corridor Buffer--4 mi: -11%,
· Corridor Buffer--12 mi: -8%, and
· Region: -6%.
Table 3.17. Change in daily VHT (2035), buffer index (2035), and estimated annual crashes (2030).
System 1 System 2 System 3 System 4
I-75/I-20W/ I-75/I-675/ I-75/I-85N/ I-75/I-85N/
I-285W I-20W/I-285W I-20W/I-285 All I-675/I-285 E
Truck- Truck- Truck- Truck-
No Percent No Percent No Percent No Percent
Only Only Only Only
Project Change Project Change Project Change Project Change
Lanes Lanes Lanes Lanes
Vehicle Hours Traveled per Day (Millions)
Facility 0.59 0.48 -19% 0.59 0.48 -19% 0.98 0.85 -14% 0.80 0.68 -15%
Corridor
Buffer = 2.68 2.37 -11% 2.81 2.50 -11% 4.60 4.11 -11% 3.70 3.34 -10%
4 Miles
Corridor
Buffer = 5.97 5.48 -8% 6.20 5.71 -8% 8.39 7.61 -9% 7.86 7.21 -8%
12 Miles
Region 10.66 10.11 -5% 10.66 10.12 -5% 10.66 9.82 -8% 10.66 9.93 -7%
Buffer Index
Truck-
Only N/A 43% -81% N/A 44% -79% N/A 40% -78% N/A 45% -80%
Lanes
GP
124% 72% -42% 124% 70% -43% 118% 77% -35% 124% 82% -34%
Lanes
2030 Estimated Annual Crashes
Total 7,867 7,860 0% 7,955 7,948 0% 13,564 13,553 0% 10,540 10,531 0%
Injury 1,708 1,686 -1% 1,727 1,705 -1% 2,944 2,910 -1% 2,288 2,262 -1%
Fatal 30 18 -40% 30 17 -43% 50 30 -40% 38 23 -39%
Reduction
in Fatal 12 13 20 15
Crashes
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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Performance Evaluation 45
Reliability Benefits. Reliability benefits in the study were evaluated in terms of change in the
Buffer Index which is the ratio of the extra time travelers must build into the trip when planning
their travel (to ensure reaching their destination on time 95% of the time), to the average travel
time. The Buffer Index was estimated as a function of the Travel Time Index (TTI, which is defined
as the ratio of the congested travel time to the free-flow travel time), using model outputs for con-
gested and free flow travel times for the no-build and truck-only lane alternatives. The reliability
benefits (in terms of percent change in the Buffer Index) were evaluated both for trucks using the
truck lanes, as well as for autos and trucks using the general purpose lanes. See Table 3.17.
Under the no-project scenarios, travelers allowed for significantly high buffer times (118% to
124%) to reach their destination on time 95% of the time (implying that their total travel times
were more than double their average travel times). The implementation of truck lanes was esti-
mated to result in significant reduction in buffer times for trucks on truck lanes (percent reduc-
tion of 80%). The reduction in buffer times for autos and trucks on the general purpose lanes
were not as significant as on the truck lanes, but still was observed to be notable (percent reduc-
tion of close to 40%). The 2035 average percentage reduction in buffer times based on the results
is as follows.
· Trucks on truck-only lanes = 80%.
· Autos/trucks on general purpose lanes = -39%.
Safety Benefits. Safety benefits were evaluated in terms of percent reduction in injury and fatal-
ity accidents due to the implementation of truck lanes compared to the no-build alternative for
each of the corridor systems. See Table 3.17. Since the Georgia study did not specifically account
for the safety benefits of truck-only lanes accruing from truck-auto separation, a 15% reduction
factor was applied to the total, fatality, and injury accidents estimates for the truck-only lane alter-
native. These results are presented in Table 3.18.
Average fatality accident reduction of 50% due to the implementation of truck-only lanes is
observed. The percent reduction for injury accidents is estimated to be lower (average reduction
of 16%), which is as expected, since a large share of the fatality accidents are influenced by the
involvement of trucks (while this share is significantly lower for injury accidents).
Assumptions and Data Gaps. Since the performance results from the study for the urban cor-
ridors scenario are based on the same procedures and tools as described for the study under the
long-haul corridor scenario, the assumptions/data gaps and their impacts on the ability to assess
the relative performance of truck-only lanes described under the long-haul corridor scenario are
applicable here as well. The procedure used to derive the reliability benefits estimates from the study,
using the Buffer Index as the performance metric, has the following potential impacts on the accu-
racy of the results:
· The Buffer Index is estimated as a function of the Travel Time Index, which implies that the
analysis only considers the reliability benefits associated with congestion reduction without con-
sidering the benefits of truck-auto separation.
· 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 accu-
racy of the Buffer Index estimates.
Puget Sound Region Freight Action Strategy (FAST) Corridor Analysis
The FAST corridor analysis project in the Puget Sound region involved the development and
application of a regional truck model (the FAST truck model) to evaluate the benefits associated
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46 Separation of Vehicles--CMV-Only Lanes
Table 3.18. Safety benefits estimates of truck-only lanes using accident data
from the Georgia study, 2030.
Safety Benefits
Truck-Only Lanes (Percentage of
Truck-Only (After 15% Reduction due to
No-Builda Lanesb Reduction)c Truck-Only Lanes)d
Fatality Accidents
System 1e 30 18 15 49%
System 2 30 17 14 52%
System 3 50 30 26 49%
System 4 38 23 20 49%
Average 50%
Injury Accidents
System 1 1,708 1,686 1,433 16%
System 2 1,727 1,705 1,449 16%
System 3 2,944 2,910 2,474 16%
System 4 2,288 2,262 1,923 16%
Average 16%
Total Accidents
System 1 7,867 7,860 6,681 15%
System 2 7,955 7,948 6,756 15%
System 3 13,564 13,553 11,520 15%
System 4 10,540 10,531 8,951 15%
Average 15%
Source: Adapted from Georgia Department of Transportation, Statewide Truck Lane Needs Identification Study.
Notes:
a. The cells in this column represent number of accidents for the no-build alternative.
b. The cells in this column represent number of accidents for the truck-only lane alternative.
c. The cells in this column represent the number of accidents for the truck-only lane alternative after accounting for
accident reduction due to truck-auto separation (a 15% reduction factor is applied to the accidents in the
"Truck-Only Lanes" column based on recommendations from the Douglas handbook).
d. The cells in this column represent the % reduction in accidents (safety benefits) due to truck-only lanes. This is
estimated from the accidents under the "Truck-Only Lanes (after 15% reduction)" and "No Build" columns.
e. Systems 1 through 4 represent combinations of individual corridors analyzed in the Georgia study.
with a variety of transportation investments impacting goods movement in the four-county
Puget Sound region. The analysis involved conducting model runs for a set of alternatives and
comparing model outputs for a set of performance measures against the future no-build alter-
native. 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). The following alternatives were considered in the study, in addition to the no-build
alternative:
· Alternative 1. "Operational" improvements of facilities, such as upgrading arterials to free-
ways, interchange improvements, and capacity improvements for trucks;
· Alternative 2. "Infrastructurerelated" improvements consisting mainly of adding general
purpose lanes and truck lanes along the larger corridor network;
· Alternative 3. Addition of truck-only lanes along the I-405 corridor;
· Alternative 4. Addition of truck-only lanes along the I-5 corridor; and
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Performance Evaluation 47
10% Alternative #1 Alternative #2
Alternative #3 Alternative #4
Percent Change in Delay Hours from
5% Alternative #5
0%
2020 Baseline
Auto Light Trucks Medium Trucks Heavy Trucks Total Vehicles
-5%
-10%
-15%
-20%
-25%
Alternative
Source: Adapted from Arun R. Kuppam and Maren L. Outwater, Evaluating Freight Mobility on a Regionwide Basis Using EMME/2
--Freight Action Strategy (FAST) Truck Model for Puget Sound Region, submitted for the 16th International EMME/2 User's
Group Conference, Albuquerque, NM, March 1820, 2002.
Figure 3.2. Percentage change in vehicle hours traveled (VHT) from 2020 future baseline.
· Alternative 5. Changes in land-use patterns for the 2020 no-build scenario, and associated
impacts.
Appendix B provides a detailed description of the performance measures and benefits results
from this study for each of the alternatives. The following sections summarize the key perfor-
mance benefits results from the study.
Performance Results
Travel Time Savings. Travel time savings is the only performance measure quantified in the
study as part of the alternatives analysis process. As mentioned previously, these benefits are gen-
erated in terms of percent change in VHT for each of the build alternatives compared to the no-
build alternative using VHT outputs from the FAST truck model. Figure 3.2 presents the VHT
results from the alternatives analysis.
Table 3.19 summarizes the percentage change in VHT for the truck-only lane alternatives (Alter-
natives 3 and 4) compared to the no-build alternative, by vehicle class and total vehicles.
Assuming the total VMT to be relatively the same along the I-5 and I-405 corridors, average
travel time savings from truck-only lanes are estimated to be around 9% compared to the no-build
alternative.
Table 3.19. Change in VHT, truck-only lanes, compared to no-build, 2020.
Light- Medium- Heavy- Total
Autos (%) Heavy (%) Heavy (%) Heavy (%) Vehicles (%)
Truck-Only Lanes -10 -4 -10 -8 -8
(Alternative 3)
Truck-Only Lanes -14 6 -19 -23 -10
(Alternative 4)
Source: Adapted from PSRC FAST corridor study.
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48 Separation of Vehicles--CMV-Only Lanes
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 study does not consider an exclusive mixed-flow lane alternative to allow for the compar-
isons of mobility performance benefits of truck-only lanes compared to adding mixed-flow
capacity.
· A travel demand model (FAST truck model) is used to evaluate the travel time savings ben-
efits of truck-only lanes. The limitations of travel demand models in assessing the mobility
performance of truck-only lanes has been discussed earlier.
· The study does not consider other key performance measures such as safety and travel time
reliability in the alternatives analysis, which are important metrics to consider, particularly as
part of the performance evaluation of truck-only lanes.
· The study does not consider differences in time-of-day distributions between trucks and autos
in analyzing the travel time savings benefits of truck-only lanes by time of day. An assessment
of the actual mobility benefits of truck-only lanes should be based on a time-of-day analysis,
to take into consideration the inherent differences in time-of-day patterns of trucks and autos
in an urban corridor environment.
I-15 Comprehensive Corridor Study
The I-15 study was sponsored by the Southern California Association of Governments (SCAG),
the California Department of Transportation (Caltrans), and the San Bernardino Associated
Governments (SANBAG) with the primary objectives of analyzing right-of-way needs along the
corridor, assessing the feasibility and costs of implementing truck lanes, and performing a com-
prehensive evaluation of transportation needs along the corridor to feed the development of a
long-range improvement plan and implementation strategy for the corridor. The study con-
ducted an initial screening evaluation of a comprehensive list of alternatives, which were narrowed
down to a final set of five alternatives for detailed screening and alternative selection process: no-
build, TSM/TDM, HOV lanes, full corridor dedicated truck lanes, and reversible managed lanes.
Traffic (truck and auto) volume forecasts and a mobility performance measure (V/C) for each of
the alternatives were generated using the 2004 SCAG Regional Transportation Plan (RTP) model.
Appendix B provides a detailed description of the alternatives, and performance benefits results
estimated in the study.
Table 3.20 shows the 2030 forecast for truck and auto volumes along the corridor by segment
(the study analyzed travel demand along the corridor for seven segments) under each of the alter-
natives. Following are some key insights from the data:
· Truck volumes are projected to represent a notable share (more than 25%) of the total traffic
volumes along most segments of the corridor.
· The data show an increase in auto traffic volumes along the corridor for each of the build alter-
natives (HOV lanes, truck lanes, and managed lanes) relative to the no-build alternative due to
the availability of additional capacity and the shifting of demand onto the corridor from adja-
cent facilities. In the case of the HOV lane alternative, this shifting of demand compensates
for the reduction in auto traffic along the corridor due to shifting of demand from single-
occupancy to multiple-occupancy vehicles.
· Auto volumes are projected to be slightly lower for the TSM/TDM alternative compared to the
no-build alternative because of the implementation of increased transit service under this
alternative.
· 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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Performance Evaluation 49
Table 3.20. Daily auto and truck volumes along I-15 by segment and alternative, 2030.
No Build TSM/TDM HOV Lanes Truck Lanes Managed Lanes
Truck Truck Truck Truck Truck
Segment* Autos Trucks % Autos Trucks % Autos Trucks % Autos Trucks % Autos Trucks %
1 103,133 34,749 25% 103,473 34,777 25% 108,985 34,835 24% 110,093 35,237 24% 113,332 34,755 23%
2 98,240 42,047 30% 98,704 42,004 30% 103,340 42,167 29% 105,404 43,079 29% 108,787 42,013 28%
3 101,608 48,330 32% 100,414 48,268 32% 102,100 48,464 32% 105,329 48,664 32% 98,301 48,120 33%
4 142,320 49,575 26% 141,585 49,547 26% 142,922 49,920 26% 147,598 50,161 25% 142,574 49,663 26%
5 96,515 39,559 29% 96,333 39,532 29% 100,713 39,885 28% 104,212 40,316 28% 99,034 39,681 29%
6 163,796 27,704 14% 163,500 27,521 14% 175,326 30,172 15% 173,552 32,319 16% 173,871 27,717 14%
7 223,860 42,250 16% 224,995 42,422 16% 245,335 46,071 16% 244,013 56,828 19% 234,762 42,477 15%
Source: Adapted from Southern California Association of Governments (SCAG), I-15 Comprehensive Corridor Study, December 20, 2005, as found at
http://www.scag.ca.gov/goodsmove/pdf/I-15_Comprehensive_Corridor_Study.pdf.[cf29]
Note:
* Segments are defined as Segment 1--Mojave River Crossing to Bear Valley Road; Segment 2--Bear Valley Road to US 395; Segment 3--U.S. 395 to SR 138;
Segment 4--SR 138 to I-215; Segment 5--I-215 to I-210; Segment 6--I-210 to I-10; and Segment 7--I-10 to SR 60.
Performance Results
Travel Time Savings. The I-15 study analyzed the mobility performance of each of the alter-
natives based on the estimation of V/C, using the SCAG RTP model. For the current analysis, these
estimates were post-processed to arrive at travel time savings benefits of the build alternatives rel-
ative to the no-build alternative. The steps involved in this process include conversion of V/C esti-
mates to average speeds along corridor segments using a volume-delay function (VDF)42. The speed
improvements for the build alternatives are then converted to equivalent travel time savings. The
travel time savings benefits estimated from this process are as follows for the 2030 forecast of the
northbound P.M. peak period average travel time savings relative to no-build:
· TSM/TDM (0% savings),
· HOV lanes (16% savings),
· Truck-only lanes (23% savings), and
· Managed lanes (29% savings).
Reliability Benefits. Reliability benefits are estimated in terms of reduction in incident-related
delay for the build alternatives relative to the no-build alternative using IDAS post-processing fac-
tors for delay per VMT as a function of congestion (V/C) and number of lanes. The incident-related
delay per VMT estimates from IDAS for each of the segments of the I-15 corridor (based on con-
gestion and number of lanes) are presented in Appendix B.
Using the percent change in daily VMT estimates (derived from Table 3.20, assuming average
trip lengths do not change significantly between alternatives), and the delay per VMT estimates
from IDAS, the percent change in incident-related delay for the build alternatives relative to the
no-build are calculated and presented in Table 3.21.
Safety Benefits. Safety benefit comparisons between alternatives are conducted by estimating
total accidents (fatality, injury, and property damage) per million VMT as a function of V/C along
the corridor (by segment) using the IDAS software, and estimating percentage change in total acci-
dents using the percent change in VMT estimates between alternatives. For the truck-only lane
42
For the current analysis, the following VDF was used: Speed = 65/(1 + [1.16 * (V/C)4.33]).
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50 Separation of Vehicles--CMV-Only Lanes
Table 3.21. Percent change in incident-related delay relative to
no-build (P.M. peak period, northbound), 2030.
HOV Truck-Only Managed
Segment TSM/TDM (%) Lanes (%) Lanes (%) Lanes (%)
1 0 -86 -88 -86
2 0 5 -88 -85
3 -1 -79 -82 -97
4 -1 -66 -70 -91
5 0 -86 -88 -87
6 0 -78 -81 -78
7 1 -70 -74 -71
Average 0 -66 -82 -85
alternative, an additional 15% reduction factor is applied to the total accidents estimate to account
for the safety benefits of truck-auto separation. Table 3.22 presents these results.
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 I-15 study does not consider a conventional mixed-flow lane alternative as part of the alter-
natives analysis process. The alternative that comes closest to a conventional mixed-flow lane
alternative is the managed lanes alternative. However, differences in operational characteristics
of conventional mixed-flow and managed lanes imply that even with similar capacities, the per-
formance characteristics of these alternatives are expected to be quite different. 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.
· Since IDAS factors only account for the reliability benefits of capacity improvement but do not
consider the benefits of truck-auto separation, the actual reliability benefits of truck-only lanes
are expected to be higher than estimated in Table 3.21.
Table 3.22. Percent change in total accidents compared to no-build
(P.M. peak period, northbound), 2030.
Truck Lanes
After 15%
Reduction
Factor
TSM/TDM HOV From IDAS Adjustment Managed
Segment (%) Lanes (%) (%) (%) Lanes (%)
1 0 -8 -21 -33 -4
2 0 -8 -20 -32 -3
3 -1 0 -12 -25 -15
4 -1 0 -12 -25 0
5 0 -9 -20 -32 -10
6 0 7 -10 -24 6
7 1 10 -7 -21 -19
Average 0 -1 -15 -27 -6
