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Performance Evaluation 51
· The study only looked at the performance of alternatives for the A.M. and P.M. peak periods.
Although this would suffice for the other alternatives, analyzing the impact of time-of-day dis-
tributions of autos and trucks in the mid-day period on utilization of truck-only lanes and the
overall performance of the truck-only lane alternative would be important to assess the applica-
bility and effectiveness of truck-only lanes in meeting performance objectives based on corridor
auto and truck demand characteristics.
3.4 Comparative Summary of Results and Conclusions
This section draws together the results of a number of different studies that all concluded in their
own context that truck-only lanes of different configurations provide positive benefits and may be
a preferred choice for improvements in both long-haul corridors and urban corridors. Although
the particular studies that are drawn on for performance evaluation are by no means exhaustive of
all the studies that have been conducted that evaluate truck-only lanes, they are representative of
the general configurations that have been evaluated and the methodologies that have been used to
conduct these evaluations. Several general conclusions can be obtained from reviewing these per-
formance evaluations. These conclusions are presented and discussed first, then followed by a dis-
cussion of conclusions that relate to each of the specific corridor scenarios (long-haul and urban
corridors) that formed the basis of this chapter.
3.4.1 General Conclusions
There are several general conclusions that can be drawn from the performance evaluations.
These include the following:
· The primary analytical tool used to evaluate truck-only lanes is a traditional travel demand
model that incorporates truck trip tables. This limits the analysis to the types of travel behav-
iors that are best captured in these models and misses many of the key potential benefits of
truck-only lanes. Operational benefits of truck-only lanes are largely absent from the analyses
or are estimated on the basis of relationships between operations and V/C ratios.
· The benefits of truck-only lanes are highly sensitive to the methods and assumptions regard-
ing diversion of trucks to these lanes (or truck lane utilization). In most of the analyses, these
methods and assumptions have been driven by the level of congestion in the mixed-flow facil-
ity and the data on origin-destination (O-D) patterns of the truck-only lanes. A more market-
focused analysis of the drivers of truck lane utilization than what was found in most of the
studies is needed to draw conclusions about the feasibility of truck-only lanes.
· Assessing the performance benefits of truck-only lanes effectively requires the definition of
appropriate alternatives as a standard of comparison. If a primary benefit driving the perfor-
mance assessment is response to congestion, then a baseline alternative for comparison pur-
poses should include other methods of alleviating congestion (e.g., equivalent capacity in
general purpose lanes).
· Despite these shortcomings, the performance evaluations do demonstrate that there are corri-
dors with high volumes of truck traffic where truck-only lanes could provide benefits to freight
users (and thus would achieve high levels of utilization) as well as to nonfreight users who
would continue to use mixed-flow facilities.
The reliance on travel demand models as the primary analytical tool used to evaluate per-
formance of truck-only lanes presents a serious drawback to the analyses. It focuses much of
the analysis on benefits that are derived from evaluation of general congestion conditions. The
standard approach is to assign multiclass vehicle trip tables to a network with and without
truck-only lanes. 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) are generally derived
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52 Separation of Vehicles--CMV-Only Lanes
from relationships between V/C ratios (i.e., general recurrent congestion conditions) and these
other benefit categories. The result is that evaluations in which there are high levels of conges-
tion in the corridor generally will show benefits for adding capacity as truck-only lanes as long
as the access and egress locations to the truck lanes are chosen to serve general O-D patterns
of the trucks. However, this approach does not adequately address some of the following pur-
ported benefits of truck-only lanes:
· Safety benefits. Relationships between lane configurations and V/C ratios were used to estimate
safety benefits in the performance evaluations and for the purposes of this project, these were
adjusted by a simple factor to account for additional benefits that accrue from truck-auto sepa-
ration. This simple factor was derived from the few studies that attempted to draw some data
from the limited applications of truck-auto separations such as the New Jersey Turnpike and the
limited applications of truck interchange bypasses. A more rigorous analysis of truck-auto inter-
actions using simulation models and more detailed statistical analysis of how truck-involved
accidents vary with the relative amount of truck traffic and congestion might identify additional
safety improvements that are associated with truck-auto separations. Research conducted at the
University of Tennessee43 on the safety benefits of truck-only lanes using simulation models has
demonstrated that this would be a potentially useful technique to conduct this type of analy-
sis. Appendix B (Section B.4) provides a discussion of this approach and the safety benefits
results from this research.
· Reliability benefits. The shortcomings with respect to the analysis of safety benefits extend to
the analysis of reliability benefits as well. None of the literature sources report any attempts to
examine how variability in speeds (and travel times) is related to truck-auto interactions
whereas at least some efforts have been made to show how crashes might be reduced through
truck-auto separations. A more thorough operations analysis capable of analyzing merge and
weave behavior, near crashes, and the different rates of recovery from crashes that are truck-
involved--versus those that are not--could provide a more definitive assessment of the reli-
ability benefits of truck-only lanes. Current Highway Capacity Manual (HCM) approaches to
conducting operational analysis are likely to be insufficient for this type of analysis because of
limitations on the percentage of trucks in the traffic stream that can be handled by this
approach. Again, simulation models appear to be a more appropriate tool.
There may be some additional shortcomings associated with using travel demand models to ana-
lyze the congestion or travel time savings benefits of truck-only lanes. A standard approach used
in modeling the impacts of truck traffic on congestion is to convert truck volumes to passenger car
equivalents (PCEs). However, given potential operational improvements associated with truck-
auto separations and the variability of truck PCE factors as a function of demand (truck share of
total traffic volume) and certain roadway geometric characteristics, current travel demand models
may not be properly accounting for changes in PCE factors as trucks and autos are separated. Thus,
it is possible that the performance evaluations conducted in the studies reviewed for this project
may be underestimating the travel time savings associated with truck-only lanes.
The general approach to estimating truck lane utilization in the studies reviewed for this per-
formance 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 diver-
sion of trucks to truck lanes when the primary motivation for using the truck lanes is to avoid con-
gestion, but a more market-focused analysis is necessary when considering routing decisions for
LCVs in long-haul corridors. The motivation for LCV operation should be based primarily on
43
A. A. Adelakun, Simulating Truck Lane Management Approaches to Improve Efficiency and Safety of Highways
in Knoxville, Tennessee, Master of Science thesis, University of Tennessee, Knoxville, December 2008.
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Performance Evaluation 53
increased productivity and potential net earnings increase to carriers. However, there are a variety
of limiting factors that may reduce this benefit because of off-setting costs of operation and lim-
ited markets. This issue is discussed in more detail later in this chapter in the discussion of conclu-
sions under the long-haul corridor scenario.
In light of how important congestion relief benefits appear to be in supporting positive conclu-
sions about the value of truck-only lanes, it is disconcerting to find how few of the studies look at
the performance tradeoffs between adding truck-only lanes versus adding more general purpose
lanes in congested corridors. Inclusion of alternatives that add equivalent capacity for mixed-flow
operations is important in determining the congestion relief benefits of truck-only lanes in com-
parison with the benefits provided by adding mixed-flow capacity. Nonetheless, the results of the
studies evaluated in this project suggest that there are likely to be many congested corridors with
sufficient truck volume to ensure high utilization of truck-only lanes. Given that benefits associ-
ated with truck-auto separation are not well captured with the current data and tools, these high
levels of utilization suggest that truck-only lanes can be a desirable alternative to other forms of
capacity expansion. This conclusion needs to be further explored with a more complete analysis of
the time-of-day characteristics of congestion and truck traffic patterns.
3.4.2 Conclusions for Long-Haul Corridors
The evaluation of truck-only lanes in long-haul corridors focused on three primary perfor-
mance measures and two primary scenarios (with and without LCV operations; the "with LCVs"
scenario only looks at longer-combination truck configurations operating on truck-only lanes
(such as turnpike doubles and triple shorts), and does not consider special permit vehicles, such
as oversize/overweight (OS/OW) trucks). As stated earlier in Section 3.2 (Step 3), the conclusions
presented here are based on an analysis of performance benefits of truck-only lanes, without con-
sideration of costs. These results are intended to provide an understanding of how truck-only
lanes perform compared to other alternatives. The planning and policy/decision making processes
for truck-only lanes call for the evaluation of the benefits of truck-only lanes (compared to other
alternatives) in relation to costs. To address this issue, the next Chapter delves into the B-C per-
formance of truck-only lanes compared to other alternatives.
The performance measures analyzed in this section were as follow:
· Productivity benefits. Measured in a variety of different ways, including reductions in operat-
ing costs or increased net earnings to truckers per day, these benefits generally are compared to
a no-build scenario. Productivity improvements are the result of reduced travel times for trucks
on the truck-only lanes and increased payloads per unit cost for LCVs.
· Travel time savings for mixed-flow traffic. By removing trucks from the mixed-flow lanes,
travel time savings can be obtained by other motorists.
· Safety benefits. Safety benefits for all motorists accrue from reduced congestion and truck-auto
separations.
The results of the performance evaluation for long-haul corridors are summarized in Table 3.23.
The key conclusions from the review of studies on the performance evaluation of truck-only lanes
along long-haul corridors are contained in the following discussion.
· In selecting the long-haul corridor scenario, it was observed that there was a high level of inter-
est 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 produc-
tivity 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
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Table 3.23. Summary comparison of performance evaluation results, long-haul corridors.
Productivity Benefits Travel Time Savings Safety Benefits
Truck-Only Lanes Truck-Only Lanes Truck-Only Lanes
No-Build wi th
LCV Without LCV With LCV Without LCV With LCV Without LCV With LCV
Operations Operations Operations Operations Operations Operations Operations
(%) (%) (%) (%) (%) (%) (%) Source
a
36 21 47 I-35 Trade Corridor Study
b
106 120 20 44 Georgia Statewide Truck Lane
Needs Identification Study
55 63c Reason Foundation, Toll
Truckways: Increasing
Productivity and Safety in Goods
Movement
4d - Western Uniformity Scenario
Analysis
Notes:
a. The study provides productivity benefits in terms of savings in truck operating costs, but without information on the share of the total revenues accounted for by operating
costs, the % increase in truck earnings could not be determined from the study.
b. These results are the relative productivity benefits of truck-only lanes (without and with LCV operations) 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).
c. LCV operations provide around 5% incremental productivity benefits compared to standard truck operations on truck-only lanes.
d. The study reports productivity benefits of LCV operations on mixed-flow lanes (compared to standard truck operations on mixed-flow lanes) in terms of % savings in shipper
costs. The information available from the study is inadequate to be able to translate these cost savings into equivalent productivity benefits in terms of increased truck
earnings.
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Performance Evaluation 55
additional capacity in the truck lanes. This is because all of the long-haul corridors that were
analyzed included large segments moving through congested metropolitan areas. In the long
run, this may be a prerequisite for successful application of truck-only lanes even in long-haul
corridors--that is, unless there is a substantial need for new freight capacity in the corridor
because of congested operations, there may not be sufficient benefit from truck-only lanes to
justify the investment. This is difficult to determine from the analyses conducted in the various
studies of long-haul corridors and without a more complete B-C evaluation.
· Incremental benefits of LCV operations relative to truck-only lanes without LCV operations are
in the range of 4% to 7% and are much less than the magnitude of productivity benefits associ-
ated with operations over long distances in reduced congestion (i.e., productivity benefits asso-
ciated with travel time savings over long-haul distances). A reassessment of the travel time
savings portion of productivity benefits in corridors with less congested operations would be
beneficial since multistate corridors that are being considered for LCV operations often have
long stretches of uncongested operations and truckers may be able to plan their routes to avoid
traveling in metropolitan areas during periods of peak congestion. Since the productivity bene-
fits are assessed on a per truck basis, it is possible that with high levels of truck usage even small
relative productivity benefits may prove cost effective when compared to costs. This will be
explored further in the next chapter on benefit-cost evaluations and points out the importance
of the level of utilization in assessing the cost-effectiveness of truck-only lanes with or without
LCV operations.
· All of the studies that considered truck lane utilization (which were most often done with travel
demand models) estimated high levels of truck diversion to the truck-only lanes, driven largely
by the need to avoid congestion. Truck diversion rates of over 65% were reported in some
studies and even higher rates of diversion were estimated in the I-35 study for LCV operations.
As noted previously, market limitations suggest that much lower diversion rates for LCVs
would be appropriate in less congested long-haul corridors because the markets may not be
present to support this level of diversion. It appears that none of the studies considered mar-
ket factors in assessing the potential rate of LCV usage on truck-only lanes.
· Two of the studies did examine the potential travel time savings for the mixed-flow traffic in
long-haul corridors with and without LCV operations and both studies showed travel time sav-
ings on the mixed-flow lanes of around 20%. In both cases, there were significant fractions of
the total corridor length that were very congested (around Atlanta, Georgia, and in the metro-
politan areas along I-35 in Texas) and the additional capacity compared to a no-build condi-
tion both encouraged truck use of the truck lanes and freed up capacity on the mixed-flow
lanes. 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) sug-
gest that it may be possible for the public sector to capture some of the value of the productiv-
ity benefits of the truck lanes through tolling while still providing sufficient benefits to trucks so
that drivers would continue to prefer the truck lanes. As part of this analysis, it would be impor-
tant to assess the impacts of incremental productivity benefits of LCV operations on truck-only
lanes on the feasibility of tolls. The Reason Foundation has conducted sensitivity analysis to
assess the return on investment (ROI) for toll truckways under various toll, truck diversion rate,
and facility cost scenarios. However, a more detailed evaluation of tolling concepts for specific
congested long-haul corridors is needed to assess the viability of tolls on truck-only lanes under
realistic long-haul corridor demand and operational conditions.
· Results from the review of studies indicate safety benefits to be significant for truck-only lanes
in long-haul corridors. This can be attributed to the mobility benefits provided by truck-only
lanes along those intercity corridor segments experiencing notable congestion (such as along the
outer boundaries of the Atlanta metropolitan area). Although the approach to estimating safety
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56 Separation of Vehicles--CMV-Only Lanes
benefits is not very sophisticated and is driven largely by improvements in overall V/C ratios, the
post-processing of results conducted as part of the performance evaluation to some extent takes
into account the safety effects of separating trucks and autos. Techniques that are able to focus
more specifically on the benefits of truck-auto separation are likely to show even greater safety
benefits. This is clearly an area where lack of field data is a critical deficiency.
3.4.3 Conclusions for Urban Corridors
The evaluation of truck-only lanes in urban corridors focused on comparisons between addi-
tional capacity in truck-only lanes and similar capacity additions in mixed-flow lanes. In order to
properly assess the performance of truck-only lanes in comparison to additional mixed-flow lanes
along urban corridors, it is necessary to have models that differentiate performance at different
times of day (since trucks and autos may have different time-of-day demand characteristics), and
the data on truck activity must properly take into account truck time-of-day demand. The per-
formance measures that were considered in the performance evaluation of truck-only lanes for
urban corridors included the following:
· Travel time savings. Travel time savings were noted for autos (and trucks) on the general pur-
pose lanes (and for trucks on the truck-only lanes to the extent to which these savings are
reported in the reviewed studies).
· Reliability. In order to evaluate projects on a consistent basis, reliability benefits are analyzed
in terms of savings in nonrecurrent (incident-related) delay, which are estimated using inci-
dent delay look-up factors as a function of V/C and number of lanes from IDAS, as described
previously.
· Safety. The approach used to evaluate safety benefits was the same as that used for long-haul
corridors.
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 per-
formance 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 mixed-
flow lanes with similar capacity. This limitation is addressed in the next chapter as part of the
B-C analysis.
· Given that the principal tool used to conduct the evaluations was a traditional travel demand
model, truck-only lanes in urban settings would only compete favorably with additional mixed-
Table 3.24. Summary comparison of performance evaluation results, urban corridors.
Travel Time Savings Reliability Safety
Mixed-Flow Truck-Only Mixed-Flow Truck-Only Mixed-Flow Truck-Only
Lanes (%) Lanes (%) Lanes (%) Lanes (%) Lanes (%) Lanes (%) Source
14 16 47 59 26 36 I-710 Major Corridor Study
29 23 85 82 6 27 I-15 Comprehensive Corridor
Study
17 39 15 Georgia Statewide Truck Lane
Needs Identification Study
9 PSRC FAST corridor study
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Performance Evaluation 57
flow lanes in settings with enough truck traffic throughout the day to achieve high levels of uti-
lization during all periods. Further, the corridor would need to have reasonably congested con-
ditions during the mid-day periods when truck traffic tends to peak, and the contribution of
truck traffic to peak-period congestion also would need to be significant (so that diversion of
trucks in the peak-period can contribute to notable relief in congestion). These conclusions
point out the necessity of obtaining better data on PCE factors for trucks in truck-only lanes as
compared to mixed-flow conditions with varying levels of congestion and percent trucks in the
mixed-flow. It is very likely that trucks have higher PCE factors when in mixed-flow conditions
even with the same level of traffic; thus the separation of trucks and autos could result in greater
congestion relief than is indicated in these studies.
· The impacts of truck-only lanes in urban corridors, as estimated in most of the existing studies,
do not adequately address potential benefits of truck-auto separation in terms of reliability and
safety. These impacts would be even more pronounced when measuring reliability and would
be related to the safety benefits of truck-auto separations as well as the general traffic flow pat-
terns. As noted previously, when trucks and autos mix, crashes are more likely and these crashes
generally are severe. The time to recover from such crashes is greater than that needed for recov-
ery from auto-only crashes and results in more significant impacts on reliability. The inability to
capture the true reliability benefit of truck-auto separation in the performance evaluations is
observed to be a major deficiency of the studies conducted to date.
This chapter pointed out some deficiencies in prior studies with regard to the performance eval-
uation 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. Although this addresses some of the deficiencies
of prior analyses, there are other issues that can only be addressed through a combination of addi-
tional field data collection, focus on specific corridors where actual traffic conditions can be taken
into account, and the application of different analytical techniques (such as traffic simulation mod-
eling). Some proposals for future research to address remaining deficiencies in the data and analy-
sis methodologies to support the performance evaluation and B-C analysis of truck-only lanes are
presented in Chapter 5 of this report. Also, the performance evaluations presented in this chapter
did not consider the application of tolls on truck-only lanes. To understand the feasibility of tolls
and their impacts on the performance of truck-only lanes, a discussion of tolls on truck-only lanes
and their implications is presented in Appendix B (Section B.5).
