28s also benefit if allowed to switch to LCVs. Trailers pulled by LCVs are

longer and have higher volumetric capacities.

Fuel productivity estimates, under a weight-limited scenario, for Rocky
Mountain and Turnpike Doubles can be calculated using regression Model 7 and
the physical and operational characteristics that are shown in Table 3-8 EEA
estimated the fuel productivity of Rocky Mountain and Turnpike Doubles to be
185.80 and 216.42 ton-miles per gallon, respectively. Comparing these
estimates to those for Twin 28s under the uncapped Bridge Formula B (Table 3-
9) provides approximations of the fuel productivity gains possible from shifts
to Rocky Mountain and Turnpike Doubles. Such shifts are estimated to result
in increases of 2 6% to 15.0% for Rocky Mountain Doubles and of 19.0% to 33.8%
for Turnpike Doubles. Of course, these benefits are not attainable on a
nationwide scale, but are attainable in those states where length restrictions
will not prohibit the operation of these LCVs when the 80,000 lbs GVW cap is

lifted and special permits are no longer required.

Shifting from 5-, 6-axle tractor-semitrailers and Twin 28s to Rocky Mountain
and Turnpike Doubles will also benefit those carriers that frequently carry
size-limited cargo Size-limited carriers are constrained by the volumetric
carrying capacity of the vehicle Table 3-10 shows the typical dimensions and
the volumetric capacities of the hauling units of 5-, 6-axle tractor-
semitrailers, Twin 28s and these LCVs The volumetric capacities of Rocky
Mountain and Turnpike Doubles are greater than those of other truck
configurations. For example, shifting from any Twin 28 to a Rocky Mountain
Double results with a gain in volumetric capacity of 2,941 cubic ft, while a

shift to Turnpike Doubles results with a gain of 5,406 cubic ft.

However, gains in volumetric capacity must be translated into fuel
productivity benefits This translation requires data describing the typical
freight densities at which size-limited vehicles operate These densities can
then be used as a baseline to calculate the potential payload gains that
result from shifts to these LCVs. Typical payloads for cube-limited tractors

pulling dry vans were determined from publications by Jack Faucett Associates.

3-32


ee-%

8.50

8.00

7.50
M
P 7.00
G
6.50
6.00
5 50

FIGURE 2-9
Average MPG By Vintage
GVW Class 7 Diesel Trucks

I

i i L 4 A. i 1 i L 1

1977 1978 i979 1980 1981 1982 1983 1984 1985 1986 1987
Model Year

Model Year 1977 Includes 1977 and

pre-1977 models


TABLE OF CONTENT

1. INTRODUCTION .
2. HEAVY-DUTY TRUCK FLEET CHARACTERISTICS .

2.1L Introduction wee
22 Data Used in the Analysis .
2.3 Characteristics of Heavy-Duty Trucks .. . oe

3. OPERATIONAL FACTORS TO IMPROVE FUEL EFFICIENCY .

3.1 Introduction

3.2 Federal Regulations on Weight .

3.3 Analytical Methodology

3.4 The Effect of Empty Mileage .

3.5 Fuel Productivity Under An Uncapped Bridge Formula B
3.6 Summary of Results

4, TECHNOLOGICAL IMPROVEMENTS TO TRUCKS .

Pr

Overview

Fuel Consumpticen Sensitivity
Weight Reduction
Aerodynamic Drag

Rolling Resistance Reduction
Improvements to the Engine
Turbocompound Diesel Engines

Drivetrain Optimization .

onnNnanaurun

Electronic Control
.10 Other Improvements

PP PP PP PR PP ew

11 Total Improvement in Fuel Efficiency

APPENDIX A: STATISTICAL RESULTS OF THE REGRESSION MODELS
TO ESTIMATE GPM

1-1
2-1

2-1
2-2
2-4

3-1

3-1
3-5
3-12
3-18
3-25
3-38

41
4-2

4-9

4-13
4-15
4-18
4-29
4-31
4-33
4-35
4-36


4, TECHNOLOGICAL IMPROVEMENTS TO TRUCKS

4.1 OVERVIEW

In the medium and heavy duty truck segments considered in the analysis, the
diesel engine has a commanding market share. The medium-duty truck market
(19,000 to 50,000 1b) is over 80 percent diesel, while the heavy-duty market
has been completely dieselized for over a decade. It is widely anticipated
that by the end of this decade, the gasoline engine may be limited to some
small specialized niches, or be used after conversion to compressed natural
gas use. This analysis concentrates primarily on diesel powered medium and
heavy-duty truck technology and the potential for improvement in fuel economy.
The analysis utilizes 1987 as a base year, and TIUS fuel economy data for 1987

are used for baseline fuel economy estimates.

Current diesel powered trucks are already very fuel efficient relative to
their weight. For example, a fully loaded 80,000 1b truck can attain a fuel
economy of 7 to 8 MPG on the highway, which translates to 280 to 320 ton-miles
per gallon. In contrast, a gasoline powered car which weighs 5000 lbs or less
fully loaded can attain a fuel economy of 26 to 30 MPG or 65 to 75 ton-miles
per gallon. It is difficult to increase the diesel trucks fuel economy by

very large amounts in the future without affecting payload capacity

Using the laws of motion and conservation of energy it is simple to show that

fuel consumption (the inverse of fuel economy) is given by’

FC = bsfe [Eg + E, + Ex) + bsfc E,, + G(t, + t,).

Na
Where, bsfc is the average brake specific fuel consumption of the engine,
Na is the transmission efficiency,
ER is the energy required to overcome rolling resistance,

4-1


HP
Range

350 to 450

290-350

240-290

190-240

<190 HP

TABLE 4-3

COMPARISON OF ENGINE WEIGHTS

(Selected Examples)

1987 vs 1991

98 e Models
lode. Weight (1b)
Cum NTC (400) 2530
Cat 3406 (400) 2840
DDC 8V-92TTA 2415
Mack EM-9 (400) N/A
Cum NTC (315) 2520
Cat 3406 (310) 2760
DDC 6V-92TTA (300) 2020
Mack EM-6 (335) 2165
Cum L10 (270) 1950
Cat 3306 (270) 2040
DDC 6V-71TA (270) 2175
Mack EM-6 (275) 2160
Cat 3208N (210) 1340
Cum 6CT 8.3 (210) N/A
GM 8.2T (205) 1120
Nav. DTI466 (210) 1475
Ford 7.8L T (210) 1395
Ford 6.6T (170) 1310
Nav DTA310 (175) 1235
GM 8.2N (170) 1095

Engine HP in parentheses

99 i le
Model

Cum NTC (400)

Cat 3406B (425)
DDC Series 60 (450)
Mack E7 (400)

cum L10 (330)

Cat 3176 (325)

DDC Series 60 (350)
Mack EM-7 (350)

Cum L10 (270)
Cat 3176 (275)

Navistar DTA 466 (270)*

Cat 3116 (250)
Cum BTA 5 9 (230)*

Nav. DT466 (210)
Ford 7 8L (210)

Ford 6,6T (170)
Cum BTA 5.9 (180)*
Nav. 7 3L (175)
Gat 3116 (185)

Engines do not have the same durability as others in this class

Ss

Weight (1b)

2530
2840
2670
2165

1870
1945
2630
2265

1950
1945

1475

1198
880

1475
1395

1310
880
790

1190


TABLE 2-4

GASOLINE TRUCKS BY USE AND BODY STYLE
PERCENT BY GVW CLASS

Agricultural Rough Use Regular Use Total”
Class 6
Non-Aero 93.9 937 613 80.7
Aero 61 6.3 38.7 19.3
Total" 42 5 17.1 40.4 100.0
Class 7
Non-Aero 94.5 94 2 65.1 82.6
Aero 55 5 8 34 9 17.4
Total* 4.1 187 40 2 100.0
Class 84
Non-Aero 96.1 969 716 89 6
Aero 3.9 31 28 4 10 4
Total” 49 3 23.7 270 100 0

* Horizontal Total reflects % of trucks in a class by type of operation.

“* vertical Total reflects % of trucks in a class by body style.

9-12


loss effect, while the change in the rolling resistance coefficient effects
only the tire losses. A study by Goodyear’ on the correlation between tire
rolling resistance and fuel economy provided data on the sensitivity to the
rolling resistance coefficient. The study was performed on a 78,700 lb GVW
tractor trailer at 60 mph. The study showed the following relationship

between the rolling resistance coefficient and fuel economy:

Rolling Resistance Fuel Economy
Value % Change Value % Change
Bias ply 43.9 Base 4.10 Base
Radial A 39.9 “9.1 4 27 42
Radial B 37.7 -14.1 4.34 5.8

The factors indicate an average rolling resistance sensitivity of 0.4. Volvo
provided data on a 80,000 1b tractor-trailer on a long haul European cycle
with tires of different rolling resistance, and the data is shown in

Figure 4-1. The data indicates a sensitivity of 0.237. This lower figure is
also indicated in the Goodyear study cited above, as the sensitivity to tire
rolling resistance decreases with decreasing speed and weight. For example,
an empty truck was cited as having a sensitivity of 0.17 to 0.2 at 60 mph
Coefficients in the range of 0 25 to 0.35 are cited by many experts. The
sensitivity factors scaling with speed or weight are not well studied. It is
also likely that the rolling resistance of drive tires that transmit torque to
the road have a greater impact on fuel economy than those used in axles that
do not transmit torque Unfortunately, there is no data to support separate

or independent analysis af those effects.

There is general and widespread agreement that typical driveline efficiencies
are 93 to 95 percent (i.e., 5 to 7 percent of engine torque is lost in the
driveline) for manual transmission equipped vehicles. Automatic transmissions
are currently sold in some medium duty trucks and in buses, which may have

higher Losses.

4-7


Another way to increase fuel productivity is to decrease the mileage when a

truck is operating empty. Empty operation takes place when a truck carries a
load in one direction but travels empty in the other. During empty mileage

fuel productivity (ton-miles per gallon) is equal to zero. Therefore, to the
extent that carriers can minimize empty backhaul, fuel productivity gains can
be realized. This section also quantifies the influence of empty mileage on
fuel productivity and investigates what can be done from a policy perspective

to minimize empty mileage.

The organization of this section is as follows: Section 3.2 outlines current
federal weight regulatory constraints in the maximization of fuel productivity
and presents the policy change that is investigated in this report, Section
3.3 describes the analytical methodology that was used to develop quantitative
estimates of fuel productivity, Section 3.4 quantifies the effect of empty
mileage on fuel productivity, and Section 3.5 quantifies the effect of a

change in the federal weight limit and the effect of LCV operations.

3.2 FEDERAL REGULATIONS ON WEIGHT

Truck weight regulations, at the federal and state level, are motivated by
concern for protecting pavements and bridges from the effects of heavy loads.
For a given truck, increasing the number of freight ton-miles traveled per
unit of fuel that is consumed implies a heavier operation weight, since the
payload weight increases and empty weight remains constant or does not
proportionately increase with payload The introduction of heavier trucks has
a direct effect on pavement wear and the safety margin for bridges, thus

increasing the cost to a highway agency of maintaining its road network

During the 1970s one of the major issues of concern to the trucking industry
was uniform truck weight regulations. Although previous federal regulation
had increased the allowable weight of trucks on the interstate system, it had
not mandated all states to comply. As a result, six states in the Mississippi
Valley and Montana retained lower limits, and truckers in interstate commerce
passing through these states were forced to operate at the lower limits or

operate illegally 2 In response to the need for uniform regulations the

3-5


and 0.5 percent on the highway is expected to result from lubricant

improvements to 2001.

4.11 TOTAL IMPROVEMENT IN FUEL EFFICIENCY

In order to predict the total impact of all technological improvements to fuel
economy, it is necessary to obtain a penetration weighted estimate of each
technology's contribution to fleet fuel economy. If, between 1987 and 2001,
the market penetration of technology i increases by m, and r, is the percent
fuel economy gain associated with the application of that technology to an
individual truck, then m.r, is the percent gain in fuel economy for the fleet
as whole. The total fuel economy improvement is-

Te Tmury

i

This assumes that there are no favorable or unfavorable synergies across all
technologies. The equations governing fuel consumption demonstrate the fact
that some fuel economy improvements are additive, and others are

multiplicative so that the above equation is conservative.

Table 4-7 summarizes the derivation of total fuel economy benefit for Class 8B
trucks. Since the sensitivities for city and highway driving are so
different, the benefit over each cycle is computed separately. For Class 8B
trucks, the largest benefits on the highway come from the combination of
aerodynamic improvement, and the use of electronic road speed governors/high
torque rise engines. Net benefits 1n city driving are much smaller since
aerodynamic benefits are negligible and road speed governors have no effect at
these speeds Nevertheless, in the absence of a 1988 NO, standard, the net
fuel economy improvement for these trucks is 22 percent (assuming a 70/30
highway/city weighting) If the NO, standards penalty is as high as 3 to 5
percent, the net increase to 2001 will be only 17.5 percent, corresponding to
1 2 percent increase per year that is nearly identical to the historical

experience between 1978 and 1987.

Table 4-8 shows that same calculations for Class 6/7 medium-duty trucks


lbs cap is, therefore, expected to induce shifts from weight-limited 5-, 6-
axle tractor-semitrailers and 5-axle Twin 28s to these heavier Twin 28s.
Bridge Formula B GVW limits allow 7- to 9-axle Twin 28s to carry more payload
and, thus, be more productive. Such a policy would not, however, affect the
nationwide operation of LCVs. Even without the 80,000 lbs cap, operation of
these vehicles would be restricted by most states’ length limits. Given that
this analysis assumes no changes in state size limits, the fuel productivity
benefits of LCVs are recognized by comparing fuel productivity between LCVs
and conventional configurations operating under the uncapped Bridge Formula B

scenario (i.e., 5-, 6-axle tractor-semitrailers and Twin 28s).

As mentioned in the introduction to this section, EEA also analyzes the
effects of empty mileage on fuel productivity. Unlike the elimination of the

80,000 lbs GVW cap, empty mileage affects all freight trucks.

3.3 ANALYTICAL METHODOLOGY

The fuel productivity analysis in this study requires only those trucks used
for the movement of freight. As a result, GVW Classes 1, 2, 3, 4, and 5
(defined in Section 2) were not included in the analysis since vehicles in
Classes 1, 2, and 3 are not predominantly used for this purpose and sales in
Classes 4 and 5 are very low. The remaining classes reflect those trucks
which are recognized by the trucking industry as predominantly commercial

vehicles.

The analysis also excluded from the “active” data base those vehicles that are
propelled by LPG or other fuels. As was shown in Section 2, on average less
than half of a percent of the trucks in each GVW class have LPG or other
engine types Disregarding such trucks was deemed appropriate since no
statistically significant results could be drawn from analyzing them. As a
result, only gasoline and diesel powered trucks are included in the fuel
productivity analysis Classes 6, 7, and 8A consist of both gasoline and

diesel trucks, while Class 8B consists of only diesel trucks.


Rocky Mountain and Turnpike Doubles from Twin 28s and tractor-semitrailers are
substantial to cube-limited carriers. As shown in Table 3-12, shifts to Rocky
Mountain Doubles result in potential fuel productivity gains that range from
39.6% to 60.4%. Shifts to Turnpike Doubles result in gains that range from
70.2% to 95.6%. Of course, these benefits are not attainable on a nationwide
scale, but only in those states where length restrictions will not prohibit
the operation of these LCVs when the 80,000 lbs GVW cap is lifted and special

permits are no longer required.

As in the analysis of fuel productivity gains from eliminating the 80,000 lbs
GVW cap, the estimates calculated for LCVs and size-limited conventional truck
configurations are derived under the assumption that trucks operate at maximum
payload and cubic capacities, incurring no empty mileage. Therefore, the fuel
productivity estimates presented under the discussion of LCVs are also
absolute maximums. The LCV discussion also assumes that fuel consumption of
Rocky Mountain and Turnpike Doubles can be estimated from the regression model
for GVW Class 8B (i.e., Model 7) Given that these LCVs have distinct
physical and operational characteristics than Class 8B trucks, Model 7 may not

be altogether representative of LCV fuel consumption.

To account for this possibility, Model 8 using data for TIUS trucks rated at
above 80,000 lbs GVW (defined as Class 9 trucks) was formulated. It is
evident from the data, however, that Class 9 includes many different truck
configurations and is not wholly defined by LCVs. To single out LCVs, Class 9
trucks were further disaggregated by type of use - rough, agricultural, and
regular. Model 8 only uses data for regular use Class 9 trucks and,

therefore, is expected to roughly represent LCVs.

Statistical results of Model 8 are presented in Appendix A, while the fitted

model is shown below.

LGPM = -1.4320-0 0092(MDLIDX)+0.0616(LWIWGT1)+0 1489(LHPCTR) -0.0591(DECO).

Using this model and data from Tables 3-8 and 3-11, an alternative estimate of

3-37


Source:

TABLE 3-1
STATE SIZE LIMITS

Save OKT | worn LENGTH FT-)
Tractor-Semmtratier Combrapora Tuan Combnators
Truce CStamet | commen cna

In Feats (Sngie ‘National engin en Sereennt | Suave

Inches In inches unit) Network" Other Rosa ‘Other Rosas Trader
‘Alabama 136 102 400 33 nA “NR 50
Alaska 140 102 40-0 “ss 70 75 18
Anzona 14-0 102 40.0 Sa/NR 85 NR NA
Armansan 13 Toe cross) 38 7 co) nS
Caltorna 140 102 400 NR 6 78 65
Colorado 134 102 400 S74 70 70 70
Connecteut 138 702 BOO zr) WR NP 60
Delaware 13-6 102 400 NR Cs) NP 80
Dist of Comoe || 19-6 102 400 NR 55 NP 58
Fonda 138 102 40-0 ‘aB7S7B gr) ial NP
Georgia 138 102 60-0 EX) 43/83 00/678 NP 60
Hawa» 136 108 400 3 45 C3 as 6s
igano 140) 102 400 aBrse 38 A at 75
thnors 136 102 420 53 53 58 6s 60
inaiana 13-6 102 36-0 53 53 NA 286 NR 60
own 138 102 05 EX) NA c) 266 60 cr
Kansas 140 102 428 508 soa MA 288 NR 85
Kentucky 13-8 102 450 53 Dal Bed 28 NP 87-9
Towsiana 138 102 05 a8 NR cy Em NR cy
Maine 13-8 102 45-0 43 “a 65 288 NP 65
Maryland 13-6 102 400 48 4a NR 28 NP 58
Massachusett® 18 102 Erin zr) a54e oO 268 WP io)
Michigan 13-8 102 400 53 50 nm $8 Se 59
Minnesota 13-8 102 400 53 53 65 20-6 NP. 65
Krasissi0p" 138 102 Eron) 33 33 NA 30 NR NA |
Missoun 13-6 102 400 53 NR Co) 28 es 6
Montana 14.0 102 40-0 53 53 NA 28-8 75 75
‘Neoraske 148 702" ~ OT SS Lae “ee os mis
Nevada 140 102 400 S3/NR 53/NA 70 28-8/NA | 70 70
New Hampstre 138 102 400 “2 48 NR 28 NP 85
New Jersey 134 102 350 a8 zr) NA EE) NP 2
New Mence 14.0 102 400 574 $76 cry 288 65 65
New York 13-8 102 400 53 “8 85 286 NP 60
North Caroine 138 02 Oo Ec A 0 268 Wwe 6
Norn Oakot® 1346 102 500 83 33 75 188 83 78 188 7s |
Ono 136 102 400 33 33 NA 26-8 NR es |
Orianoma 13-6 102 450 36 $3 NR 29 NR 70
Oregon 140 102 40-0 33 NR 60 68 60 78
Pennayivania 13-8 102 40-0 53 NR 80 286 NP 60
Roce Isiend 136 102 40-0 48-8 488 NR 286 NP NS |
South Caroline 13-6 102 400 53 43 NA 288 NP NR
South Dakot®. 140 102 46-0 53 83 NR 816 B16 80 |
Tennessee 138 102 20 50 30 NA 268 NP 6s
Texas 134 102 450 39 58 NR 288 NA 38
Uten 14-0 102 450 48 153 48 NR a1 61/NR 65
Vermont ey 02 rox) er) “a57NA Ca 7 Ne 80
virgins 13-8 102 40-0 83 NR 6" 286 NP 60
Washington 140 102 400 48 43 NR 60 60 7 |
West Virgins 13-8 102 400 53 NR 60 28 NP 60}
Wisconsin 136 102 40-0 53 NR 60 284 NP 60
wyommng 140 102 60-0 60 60 NA 80 80 as

ATA, size and Weight Limits, July 1990.

3-8



REFERENCES

1. American Trucking Association, Summary of Size and Weight Limits,
Alexandria, Virginia, July 1990.

2. Transportation Research Board, Special Report 225, Truck Weight Limits:
Issues and Options, Washington, D.C., 1990, pgs 43-44.

3. Transportation Research Board, Special Report 211, Twin Trailer Trucks,
Washington, DC., 1986, pg 49.

4. Transportation Research Board, Special Report 225, Truck Weight Limits-
Issues and Options, Washington, D.C , 1990, pg. 160.

5. Transportation Research Board, Special Report 225, Truck Weight Limits:
Issues_and Options, Washington, D.C., 1990, pg. 50.

6. Transportation Research Board, Special Report 225, Truck Weight Limits-
Issues and Options, Washington, D.C., 1990, pgs. 66-67.

7. Trucking Research Institute, Productivity and Consumer Benefits of Longer
Combination Vehicles, Washington, D.C., May 14, 1990, pg. B-6.

3-40


TABLE 4-7
IMPROVEMENTS TO CLASS 8B
TRUCKS, 1987 - 2001
(Percent Improvements in Fuel Economy)

Technology Market City F/E Highway F/E
Penetration Increase

Weight Reduction (0.75%) 100 0.40 0.25
Drag Reduction Van Bodies 50 0.28 6 75
Other 35 0.07 1 60
Rolling Resistance 65 1.85 2 90
Engine Improvements 100 5.50 5.50
Turbocompound 10 0.30 0 50
Drivetrain Optimization N/A 1.50 2.00
Electronic Control 100 2.50 6 00
Lubricants 100 1.00 0 50
1300 26 00
Potential Effect of NO, Standard (-3.00) (-5.00)

4-37


combination explains this insignificance. The exact opposite was found to be

true for diesel vehicles.

The statistical results of the chosen regression models are presented in
Appendix A. The significance probabilities, or p values (shown in the output
tables as Prob > [tT], indicate that the estimated coefficients are
significant above the 95% significance level. The fitted models are presented
in Table 3-5.

3.4 THE EFFECT OF EMPTY MILEAGE

Empty mileage usually takes place when a truck carries an empty backhaul

(ie , carries a payload in one direction but not in the other). ‘The 1980
Interstate Commerce Act abolished backhaul restrictions on the federal
interstate highway system. Today any carrier which obtains Interstate
Commerce operating authority - and does not, for example, carry food produce
in one direction and hazardous waste in the other, as stipulated by the recent
"Garbage Bill" - is free to carry backhaul loads and avoid empty mileage when
traveling the interstate roads. However, the ability of a carrier to avoid
empty mileage largely depends on logistical and managerial factors within the
carrier’s trucking company and on state laws regarding intra-state backhauls
This section estimates the effect of empty mileage on fuel productivity and

discusses possible policies that may minimize empty mileage.

The effect of empty mileage on fuel productivity can be estimated using the
variables and regression models that were developed by EEA and explained in
Section 3 3. If a vehicle experiences empty mileage in a given trip, then the
vehicle’s operating weight is represented by AVWGHT, or empty weight plus
typical cargo weight. However, a vehicle on any given trip will incur some
empty mileage and some loaded mileage. In such situations, the vehicle's
operating weight will equal EQUIVWT, which is defined as the weighted sum of
AVWGHT and EMWGHT WTDWGT3 must be used to estimate fuel consumption (GPM)
when a truck operates empty, since it reflects a vehicle's operating weight

when empty WIDWGT2 should be used to estimate fuel consumption when a truck

3-18


TABLE 4-5
BSFCG FOR SELECTED

1991 ENGINES (LB/BHP-HR)

Class Model HP RPM. BSFC
Light Heavy Navistar 7.3L 185 2800 0 550
Cummins 5 1L 100 2500 0.400
Medium Heavy Ford 6.6L 170 2300 Q 440
Navistar DTA 360 185 2700 0 445
Caterpillar 3116 185 2600 0 396
Ford 7.8L 210 2300 0.404
Navistar DTA 466 230 2400 0.418
Heavy-Heavy DDC Series 60 (11.11) 275 1800 0.372
(<350 HP) DDC 68-92 300 1800 0.448
Cummins L10 310 1800 0.378
Caterpillar 3176 325 1800 0 344
Heavy-He avy Caterpillar 3400 PEEC 460 1900 0 358
(>350 HP) DDC Series 60 (12.7L) 450 2100 0.367


TABLE 2-1
DISTRIBUTION OF TRUCKS BY
ENGINE TYPE AND GVW GLASS

GVW Class % Gasoline % Diesel %_LPG % Other?
Class 6 68.8 30.4 0.6 0.2
Class 7 52.9 46.4 0.5 0.2
Class 8A 20.5 79.3 ol 0.1
Class 8B 0.0 100.0 0.0 0.0

1 Qther includes those trucks for which engine type was unknown.


Figure
Figure
Figure

Figure
Figure
Figure
Figure
Figure
Figure
Figure

Figure
Figure

Figure
Figure

Figure

2-4
2-5
2-6
2-7
2-8
2-9
2-10
2-11

3-1

4-1
4-2
4-3

LIST OF FIGURES

Average CID By Vintage and GVW Class Gasoline Trucks
Average Horsepower By Vintage and GVW Class .

Average Percentage of Annual Mileage When No Load Was
Carried, By GVW Class... ... . . toe

Average Operating Equivalent Weight By GVW Class
Average MPG By Vintage GVW Class 6 Gasoline Trucks
Average MPG By Vintage GVW Class 7 Gasoline Trucks
Average MPG By Vintage GVW Class 8A Gasoline Trucks .
Average MPG By Vintage GVW Class 6 Diesel Trucks
Average MPG By Vintage GVW Class 7 Diesel Trucks
Average MPG By Vintage GVW Class 8A Diesel Trucks
Average MPG By Vintage GVW Class 8B Diesel Trucks .

Truck Types .

Long Haul Central Europe
Long Haul Central Europe

Effect of Reducing Friction on Engine Efficiency

iv

2-15
2-17
2-18
2-19
2-20
2-21
2-22
2-23
2-24

3-2

4-8
4-17
4-24


As a result, EEA used TIUS variables to define new variables that more
accurately explain the factors that determine fuel productivity so that
regression analysis could be employed to quantify the effect of physical and
operational characteristics on a vehicle’s fuel consumption rate (GPM). These
EEA variables are defined in Table 3-4.

The variable WIDWGT1 is of special interest to the fuel productivity analysis.
WIDWGT1L is defined as follows:

WIDWGT1 = ((AVWGHT*FRCLOAD)+( EMWGHT*FRCNLOAD) } /EEAMAX ,
where EEAMAX is defined as the high end of the GVW range for the vehicle in
question. Therefore, WIDWGT1 describes the actual operating weight of the
vehicle normalized to that vehicle’s weight category The numerator of
WIDWGT1 describes the weighted sum of the vehicle’s average operating mass by
employing as the weights the loaded to empty mileage ratio and the empty to
loaded mileage ratio. The effect of WIDWGT1 on GPM is expected to be positive
since the greater a mass the more energy input that is required to propel that

mass into motion.

Engine control variables for engine size and horsepower were defined by EEA
using TIUS variables, namely CID and HRSPWR. The purpose of EEA‘s CIDCTR and
HPCTR variables was to recognize the effect of engine size or horsepower on a
vehicle's fuel consumption rate. The expected relationship being that
vehicles with large engines or high horsepower ratings have higher average
GPMs

A vehicle’s age is also expected to directly impact GPM, with older vehicles
being relatively less efficient in the consumption of fuel than newer
vehicles, given recent technological advances in engine and vehicle design
that have improved fuel economy. To recognize this effect, EEA used TIUS's
MODELYR variable to create MDLIDX.


found to be 0.170. Fuel savings were measured on track tests conducted at 55
mph. Fuel economy increased from 6.3 mpg without the device to 6.93 mpg with
the device, providing a sensitivity of 0.453 for drag reduction. Truck
industry experts confirm that a 10 percent drag reduction provides about 5
percent fuel economy benefit at highway speeds closely matching the calculated
coefficient. The Volvo data indicates a coefficient of only 0.25 which
appears low but is consistent with the high inertial loss claimed by Volvo.

Since the sum of aerodynamic drag forces and inertial & rolling resistance
forces represents the total force to be overcome, the drag sensitivity
coefficient is related to the inertial & rolling resistance (weight) sensitiv-
ity coefficient. The reduced weight sensitivity coefficient translates to a
higher drag sensitivity for medium-dury trucks. At highway speeds, medium-
duty trucks can have a coefficient for drag as high as 0.75. This is
consistent with engineering expectation since the product of drag coefficient
and frontal area is nearly constant for all trucks from Class 6 to 8B while
weight varies by a factor of 4. Hence, at the lightest weight, drag is a much

more significant factor than weight at the same speed.

Power consumed due to aerodynamic drag scales as the cube of speed. At city
speeds of 19 mph, the highway sensitivity coefficient for a Class 8 truck
should decrease by the cube of the speed ratio, hence
Sensitivity at 19mph = 0 453 x ti? | 3
- 0.019 ©»

The small coefficient has not been verified by confirmatory testing. A
similar calculation for Class 6/7 truck at 19 mph indicates a sensitivity

factor of 0.031,

Tire rolling resistance changes have a large effect on fuel economy It
should be noted that total rolling resistance is a function of both truck
weight and the tire rolling resistance coefficient. The weight effect

calculated includes both the rolling resistance effect and the reduced inertia

4-6


Navistar’s simulation analysis suggests significant potential for drag
reduction simply by introducing a radius of curvature for the top and vertical
corners in a van. A rounded corner van body was found to have a 30 percent
drag reduction relative to a square corner van body. Roof fairings for
medium-duty trucks can produce drag reductions of up to 4 percent, but are
difficult to ‘tune’ due to the lack of space to mount the deflector. Problems
with consumer acceptance of rounded van bodies, as well as lack of development
of van aerodynamics suggests these improvements are unlikely to be realized.
Navistar suggested that 5 to 8 percent additional aerodynamic drag reduction

would be realized from market forces alone.

Volvo and Navistar suggested that the van aerodynamics problem had not been
well addressed because van bodies were independently manufactured by small
manufacturers, who did not have the resources to develop low drag designs.
Tractor- trailers integration was another area where manufacturers’
representatives believed that further scope for cost-effective improvement was
available, but market forces were insufficient to cause these improvements to

occur

4.5 ROLLING RESISTANCE REDUCTION

The advent of radial tires brought about significant decreases in rolling
resistance, and a large majority of trucks now use radial tires Bias-ply
tires are limited to some rough terrain applications (construction) or in
garbage haulers where there is potential for sidewall damage. Low profile
radials were the next improvement available in tires, and currently have about
35 percent of the market. Low profile radials have 8 to 10 percent lower
rolling resistance than conventional radials, and reduce the operating height
of the truck. Low profile radials also have lower weight, and hence a tax
advantage as tires are taxed by weight. These factors suggest that low
profile radials will essentially displace conventional radial tires over the

next 5 years.


ANALYSIS OF HEAVY DUTY TRUCK
FUEL EFFICIENCY TO 2001

Prepared for:
ENVIRONMENTAL PROTECTION AGENCY
Energy Policy 3ranch
Washington, D.C.

Prepared by:
ENERGY AND ENVIRONMENTAL ANALYSIS

1655 North Fort Myer Drive, Suite 600
Arlington, Virginia 22209

September 1991


MODEL 1
Dependent Variable: LGPM

-- EEA G¥W Group*19,500-26,000 tha Type of Cuel used by vehicle-Gasolin

Analysts of Variance

Sum of Hen
Source oF Square Square F Value ProboF
Hodel ry 24 94020 6 29305 64 386 © g001
Error 4133 400 48378 0 09690
€ Total 4137-425 42397
Root HSE 0 31129 R-aquace 0 05086
Dep Mesn 2 94409 Adj R-aq 0 0577
cv. -16 98020
Parameter Estimates
Pavemeter Stendord T for HO
Variable OF Estimate Exror Paremeter-0 = Frob > JT]
ANTERCER 1 © -1 780038 =O 1654015 107 98 © copa
HoLiox 1 -0 004928 = 00193149 “2 352 0 o108
> twTMGTE I © 234598 = 0 02474108 9 4B2 9 0002
uctoctR «1 9 440347 0 o3908487 11 266 © 0001
cal DLOcAL 0 030265 8 (01325301 3.793 © ooo2

Correlation of Estinetes

CORRS INTERCEP POLIDK LWTHGT: LcrocTR LOCAL
INTERCER 1 9900 -D 4183 0 se77 0 0409 -0 6863
MDLIDX -0 4183 1 0000 -0 1060 0 2322 0 1158
LwTWGT) 0 se77 -D 1040 41 ao00 -0 131 0 a2s0
LCHDCIR -0 0809 -0 2122 0 1311 1 o000 0 asa9

DLOCAL. -0 6863 o 1158 0 0250 0 0649 2 Go00


Table
Table
Table
Table

Table
Table
Table
Table

a5
4-6
4-7
4-8

LIST OF TABLES

(Continued)

Sensitivity of Fuel Economy to Truck Load .
Weight Savings for Specific Aluminum Parts
Comparison of Engine Weights

Engine Manufacturers Association Brake Specific Fuel
Consumption Heavy-Duty Diesel Engines .

BSFC For Selected 1991 Engines (LB/BHP-HR)
Improvements to Engine BSFC, 1987-2001
Improvements to Class 8B Trucks, 1987 - 2001
Improvements to Class 6/7 Trucks, 1987 - 2001

iii

Page
4-5

4-10
4-12

4-19
4-20
4-27
4-37
4-38


t-¥

CORRE

INTERCEP
MOL IDX
LATWGTI
LHECTR
DLOCAL
DAERO

MODEL 2

Dependent Variable: LGPH

-+ EEA GYW Group=19,500-26,000 Lbs Type of fuel used by vehicle-Oie

Analysis of Variance

Sum of Mean
Source oF Squares Squere F Value ProboF
Model 3 2s 00105 4 80021 1 665 © 0001
Ercor 2006 «134 36455 © asess,
€ Total 2011 158 36559
Root MSE 0 25681 R-aquare 9 1316
Dep Moan 7199331 Adj R-9q 0 1494
cv -12 98381
Peremeter Estimat
Poremeter Standard T for RO
Variable OF Estimate Error Perameter-0 = Prob > [T|
INTERCEP 1 -1 705384 =o o1e05094 -98 908 0.0000
MDLIDX 1 -a 027829 = 0 00174207 -1S 975 9 0001
LWIWGTL o£ 0 220867 =p 03427749 64a 0 0001
LHPCTR 1 0 096602 =p 0512199) 1 266 0 0594
DLOCAL 1 0.033743 9 01226845 2 750 0 oso
DAERO 1 -0 069142 0 02273189 -3 042 © 00z4
Correlation of Estimates
INTERCEP. HDLIDK LATWGTI LaecTR LOCAL
1 0900 -0 6522 0 3693 -0 0283 -o 5169
-0 6522 1 D000 -9 gazo 9 1331 9 1532
0 5693 -0 0820 1 ooo 0 0176 9 0207
-0 0283 0 1338 0 0176 1 0000 0 0106
-0 5189 0 1332 0 0207 O 0106 1 a00a
-o 0076 -0 1641 0 0090 -0 0453 0 0286

AERO

-0 0076
-0 1681
0 o090
-0 0453
a 0206
1 oa00


and 80,000 lbs GVW. Seven-axle, 8-axle, and 9-axle Twin 28s generally operate
beyond 80,000 lbs GVW (the current legal maximum) under special permit in
accordance with applicable state laws. A double trailer combination with one
or both trailers longer than 28 ft is defined as a Longer Combination Vehicle
(LCV). The definition of LCVs is not consistent within the trucking industry.
Some define 7-axle, 8-axle, and 9-axle Twin 28s as LCVs, since these
configurations hardly ever operate below 80,001 lbs GVW Others, including
EEA, consider only those double trailer combinations with one or both trailers
longer than 28 ft operating at weights that exceed 80,000 lbs (under special
permit) as LCVs In this context, the most common types of LCVs are Rocky
Mountain Doubles and Turnpike Doubles. Rocky Mountain Doubles are 7-axle
double trailers commonly having one trailer that is 28 ft long and another
that is 48 ft long. Turnpike Doubles are 9-axle double trailers whose
trailers are usually both 48 ft long. Triple trailer combinations (i.e , a
tractor unit with three 28 ft trailers) are also common in some states,
operating under special permit. However, because of their specialized
applications and physical characteristics, an analysis of triples is beyond

the scope of this report.

One way to change fuel productivity is to increase the payload capacity of a
truck Payload capacity is determined by the difference between a vehicle's
empty weight and a vehicle's maximum gross vehicle weight (GVW). A vehicle's
maximum practical GVW is defined by a carrier's needs and by state and federal
regulations on truck size and weight. Truck weight limits constrain GVW by
restricting a vehicle’s maximum operating weight, while truck size limits

constrain GVW by restricting a vehicle's volumetric carrying capacity

Liberalizing weight limits to allow trucks to operate at higher GVWs directly
influences fuel productivity. A vehicle’s empty weight does not increase in
step with GVW, so a more liberal weight limit increases the payload capacity
of the vehicle. Increasing payload capacity compromises fuel economy (as

defined by miles traveled-per-gallon of fuel that is consumed, or MPG) since
the added weight requires more energy input to propel the vehicle into motion

However, in the context of fuel productivity, the potential payload capacity


than 0.5 percent. Between 1987 and 1991, however, a very large fraction of
the medium-heavy-duty engine segment began utilizing intercooling with a fuel

economy benefit of 5 percent.

Electronic control of fuel injection allows optimization of injection timing
and "shaping" of the "torque rise" curve. Some of the 1991 engines have
electronic injection timing control offered as an option, such a Caterpillar’s
PEEC model, while it is standard on some engines such as the Detroit Diesel
Series 60. Comparison of bsfc data from mechanically controlled and
electronically controlled engines do not consistently support a fuel economy
advantage, but the effect of the controls can be to change driving practices
and allow the incorporation of speed control, which are discussed in Section
4.9 and 4.10.

Improvements to air utilization can be achieved by moving the piston top ring
closer to the upper edge of the piston and by optimizing valve lift and
duration. At this point, no manufacturer is considering variable valve
timing, but it is a possibility only for the post-2000 time frame. Improved
air utilization will help in reducing particulate emissions, but is expected

to provide very little benefit to fuel economy.

CompresSion ratio (CR) increases are possible for the future, according to
some manufacturers. Caterpillar and Volvo believed that CR could increase by
0.5 to 0.8 over the next decade, providing a 1/2 percent increase in bsfc.
Cummins and Mercedes believed that NO, emissions would limit further CR

increases and no benefit would result.

Improvements to turbochargers can arise from better matching of turbochargers
as well as variable geometry turbocharging. Most of today's engines select

"off-the-shelf" turbochargers that compromise peak efficiency and matching of
characteristics over the load/RPM range. Variable geometry turbochargers have
the capability to improve the matching characteristics over the operating RPM
range, and improvements to turbine and compressor efficiency could add 1.5 to

2 percent in fuel efficiency at operating points that are not close to the


Figure 4-2

Long haul
Central Europe

18 22 26
Number of wheels

2001-82-€2 16.13 BY Tebs3e2 Preduced eat VOLVO


classes However, Figure 2-2 does not support this conjecture. No trends in
average horsepower ratings are apparent in any of the GVW classes. The reader
is cautioned that TIUS data on engine size and horsepower does not specify
each truck’s actual engine size or horsepower rating. Rather, the survey asks
the responder to classify the truck into engine size and horsepower ranges
that are provided by TIUS. The data shown in Figures 2-1 and 2-2 describe the
average of the midpoints of the range for each vehicle in a given GW

category.

Besides engine size and horsepower, other physical attributes impact a truck's
fuel efficiency. For example, fuel economy options like aerodynamic drag
reduction devices, engines with low RPM, high torque rise, turbocharger,
variable fan drives, radial tires, or axle/drive ratios that maximize fuel
economy have important effects on average fuel consumption rates across truck
classes. Table 2-3 presents the penetration rates of these fuel economy
options by GVW class/engine type combination. The penetration of aerodynamic
devices is more prevalent than any other fuel economy option. Newer trucks
are designed with aerodynamic features, and, with the exception of radial

tires, this technology is the most cost efficient to retrofit

However, in order to understand the future market penetration of technologies
that truck buyers can select as options, it is necessary to know the
operational characteristics of trucks by GVW class. While lubricant
improvements, weight reduction, accessory drive improvements, and transmission
improvements are applicable to all trucks, and are usually incorporated into
the standard truck, aerodynamic drag reduction devices, radial tires and speed
control devices are driver (or owner) selected options. For example, radial
tires are not purchased by consumers who operate their trucks in ‘rough’
conditions because radial tires are more susceptible to sidewall damage than
bias ply tires Similarly, aerodynamic drag reduction devices are only useful
in trucks that have enclosed vans (dry vans) or trailers, and with tank
trucks On open trucks (such as flatbeds, cattle racks, and dump trucks) drag
reduction devices offer no useful fuel economy improvements TIUS data was

used to estimate the percent of trucks operated in rough and agricultural

2-9


Empty Weight (lbs)!

GVW Under 80,000 1b
GvW Cap (lbs)

GVW Under Uncapped
Bridge Formula (lbs)

Payload Under 80,000 1b
GVW cap (lbs)

Payload Under Uncapped
Bridge Formula (lbs)

LHPCTR,2
LHPCTR,?
MDLIDX

% w/DLOCAL=1
% w/DAERO=1
% w/DECO=1

1 Empty Weights reflect

TABLE 3-8

PHYSICAL AND OPERATIONAL CHARACTERISTICS

OF WEIGHT-LIMITED 5-AXLE OR GREATER TRUCKS

5-Axle 6-Axle 5-Axle
Semi. Semi. Twin 28
26,800 28,300 30,000
80,000 80,000 80,000
80,000 86,000 91,500
53,200 51,700 50,000
53,200 57,700 61,500
0.1068 0.1068 0.1068
0.1068 0.1791 0 2411
11 1L 11
17.6 17.6 17.6
100 100 100
22.0 22.0 22.0

tractors pulling dry vans

7-Axle 8-Axle 9-Axle Rocky Mt Turnpike
Twin 28 Twin 28 Twin 28 Doubles Doubles
34,200 36,700 39,200 36,000 45,000
NA NA NA NA NA
99,500 104,500 110,000 108,500 131,700
NA NA NA NA NA
65,300 67,800 70,800 72,500 86,700
NA NA NA NA NA

O 3249 0.3739 0.4252 0.4115 0.6053
11 11 iL il 1L

17.6 17.6 17.6 17.6 17.6
100 100 100 100 100
22.0 22.0 22.0 22.0 22.0

Empty weight varies by trailer types and length of trailers
2 LHPCTR estimates reflect AVWGHT of 35.95 tons for Class 8B trucks (Table 3-6).
NA: Not applicable since these configurations seldom, if ever,
operate below 80,001 lbs.


At this point, it is difficult to estimate the effect of the 4.0 g/BHP-hr No,
emissions standard required by the revised Clean Air Act for 1998 and beyond.
Many diesel engine manufacturers believe that further NO, reduction from
current Levels would be very difficult to achieve without timing retard.
Timing retard would result in significant reduction in fuel economy of 3 to 5
percent. However, Navistar was an exception, and its staff stated that fuel
economy effects of the 4.0 NO, standard would be relatively small. Manufac-
turers need not use any timing retard if several new technologies under
investigation prove successful. Among these technologies, the new zeolite
catalysts appear promising in that tests with diesels have shown NO, reduc-
tion sufficient to meet even a 3.0 g/BHP-hr standard, Of course, these test
results are preliminary and the durability of these catalysts is unknown.
Nevertheless, there is poCential to meec che 4.0 g/BHP-tr NG, standard with no
fuel economy penalty. Other cechnologies, such as incorporation of exhaust
gas recirculation, reduced compression ratio and/or variable valve timing may
be used singly or in combination to attain the 4 0 g/BHP-hr standard with less

fuel economy penalty than if the standard was obtained by timing retard alone.

4.7  ‘TURBOCOMFOUND DIESEL ENGINES

Turbocompound diesel engines were extensively researched by the Department of
Energy (DOE) in the late 1970’s and early 1980's. Despite a successful
technology development program that suggested significant fuel efficiency
benefit, the technology was not commercialized. The DOE-Cummins joint
development program that was essentially complete in 1982 involved the
assembly of a 450 HP turbocompound diesel that met the 6.0 g/BHP-hr NO,
standard. The turbocompound engine provided a fuel consumption reduction of
15 to 16 percent over a production 1982 NTC-400 horsepower engine used as a
reference. However, the turbocompound engine used a number of component
refinements, and Cummins determined that the benefit of turbocompounding alone
was 4.2 to 5.3 percent. Additional advances in the exhaust manifold design,
and insulation of the exhaust flow path resulted in an additional 6 percent
improvement over the initial turbocompound design. A minimum bsfc of 0.298
1lb/BHP-hr was attained at 1500 RPM.

4-29


Figure 4-1

Long haul
Central Europe

Fuel,(J/100km)

eee pee teteeegeeeeeees peter eee yreeeeeees ied e eee e ges ete yeceeeeeepeeeeeeee peeeeeeee peters eeeg ener e ees eee

40-4-— Ft tt tt ttt
50 52 54 56 58 60 62 64 66 68 70 72 74
Rolling resistance (N/ton)

1001-82-61 14.53 BY Teessez Produced at VOLVO


Table 3-2

INTERSTATE NATIONAL NETWORK ALLOWABLE GROSS WEIGHT

(FEDERAL BRIDGE FORMULA!

GROSS WEIGHT LAW FORMULA B W= SOO(LN/N-t + 12N 1 36)

States have adopted the Federal Bridge Formula tor travel on the Interstate and other public W maximum weight in pounds cared on any group of two or more axles computed to
highways eilher by lormula (Formule 8) of by chart (Table B), with the exception of the states nearest 500 pounds

found at Table A Variations may occur due lo rounding tanguage adopied or not adopted by 4 = distance in tect belweenthe extremes of any group af two or more consecutive axles

jale Table B appears 8s provided by the Federal Highway Admuni: N = number of axles in group under consider

TABLE B (in 1,000 tbs.)

Distance in toot Maximum toed in 1000 he Distance In Maxtemem load in 1000 fe
between the ex- cortied on any group of 2 between the carsled on any group of 2
tromes of ony group oF more consecutive exten tremes of any group OF more consecutive axles
01 2 of more con- - or or con-
eocutive axles 2 F Py 8 e ? 8 ° secutive axtes 2 3 4 8 6 ? °
antes | antes | antes | extes | extoo | anton | antes | antes antes | eutos | antec | axtoe | oxtes | antes | axtee | exten
‘ Mo * 126 ors °
8 340 a 8 a20 oo
6 300 o a0 s00
7 Bao ery ass 08
© ond teas 30 ° 80 ao 1000
qore then 8 300 0
. 300 8
0 200 6 4 o | aes 1005
82 s | sso rf 110
° 83 o | eo ° 1020
“0 a s | es 5 1028
8 35 5 | eo | sz0 1030
ry
470 se azo | ors | ozs 1033
sr o35 | s0 | 930 1040
420 se seo | wo | seo soa3
a so eso | cos | oes 108.0
os 60 os | soo! eso tos 5
too
we 20 610 seo | sos | oss 1088
: eos | s10 | seo 107 0
wo Fa ss ors | ozo | os 107 8
a2 628 goo | 028 8 a0
23 830 os | 930] 0 was
20 se0
23 Lary woo} ss | cos 1080
goo} m0 | 1008
n 338 sos | oo | ees | s0
Ha seo ero | 935 | 100 | 18
Ey a0 e209 o5 | 0 | toro | wo
» 315 25
30 805 630 " szs | sos | sors | woes
n o0 | 70 | sro | wo
a s00 033 a e385 | o00 | sors | tore
ET 00 eas | wo 1 eso | oes | s030 | sos!
Ec eso | sos % eso | #0 | 1038 | 100
TM as | oo
Ey coo | o 19 oss | 005 | 100
" seo | sooo | tos
= ees | sz0 10 ees | wro | 108
a ero | s30 9 ors | tors | toe
ers | 933 ° seo | w20 | 00
= eos | 90
°o eo | oes o sos | so2s | wra
a wo | sao | toeo
a“ cos | wo a ooo | sao | 088
a woo | 935 oa sas | 1090
sos | seo es 1080
o | 9
15 9s 08 L$
rs er 1080
ee 1070
J 107 8
90 1080
2 08 3
32 000

end nae mol mecannendy been adopted Dy mdrsdual alatee

Source: ATA, Summary of Size and Weight Limits, 1990.


Tt-€

ff of Obs
ANNMIL
MPG
EMWGHT?
AVWGHT?
FRCNLOAD
EQUIVWT?

MDLIDX?

% w/DLOCAL#1
% w/DAERO=1
% w/DECO=1
LHPCTR
LCIDCTR
LWTWCT1
LWTWCT2
LWTWGT3

TABLE 3-6
STATISTICAL MEANS OF SELECTED

VARIABLES BY GVW CLASS AND ENGINE TYPE COMBINATION

- GW Class 6 - - GW Class 7 - - GVW Class 8A -
Gasoline Diesel Gasoline Diesel Gasoline Diesel
5,159 2,425 2,401 2,238 2,166 8,973
7,160 19,320 7,720 20,235 8,230 27,725
5.96 6.94 5 68 6.58 4.83 5.32
5 53 6.70 6.58 7.85 8 44 10.94
11.15 11.32 14.34 14.62 21 43 23.11
0.36 0.29 0.36 0 28 0.41 0.33
9.00 9.95 11.34 12.68 16.00 18.91
2 21 5.45 2 39 5.33 1 84 3.80
84 40 66.10 86.20 66.40 86.30 63.40
1 00 6.30 1.40 6.40 0 90 9.80
0.10 2.80 0.80 3.00 0.20 5.60
- -0.0099 - -0.010 - -0.0485
-0.0077 - -0.0081 - -0 0027 -
-0.3863 -0.2817 -0.3967 -O 2793 -0 6499 -0.4865
-0 1633 -O 1478 -0.1483 -0.1287 -0.3510 -0.2801
-0.9035 -0.7085 -0.9781 -0.7936 -1 312 -1 0604

1 Expressed in tons.

2 This second block of variables give regression values used in estimating GPM.

cvw
Class 8B
Diesel

19,
65,
5
13.
35.

0.
28.

25.
22.
15.
-0.

-0.
-O.
1.

974
750

-05

75
95
31
93

-16

40
50
90
0127

3444
1200
1034


affected by a policy that eliminates the 80,000 lbs GVW cap. Moreover, not
all vehicles in GVW Class 8B will be affected by a policy that eliminates the
80,000 lbs GVW cap. Carriers that often carry light-density freight will
rarely be weight-limited. These carriers will be limited by volumetric

capacity and restrictions on the vehicle's size.“* On the other hand, those
vehicles in GVW Class 8B that carry high-density freight are often weight-

limited by the 80,000 lbs cap.

To distinguish between the operational and physical characteristics of weight-
limited vehicles versus all vehicles in GVW Class 8B, EEA employed TIUS'
PCARWT variable Those vehicles in GVW Class 8B that exhibited a PCARWT value
of greater than 75% were identified as being weight-limited by the GVW cap.
Out of 19,974 vehicles in this class 3,276 met this criteria. However, TIUS
data for GVW Class 8B does not distinguish between 5-axle, 6-axle, 7-axle, 8-
axle, and 9-axle vehicle configurations To get around this problem EEA
assumed the following:

* MDLIDX to be 11 and DAERO to be 1 for all configurations so

that fuel productivity comparisons are made only between new
vehicles equipped with drag reduction devices.

« For all configurations, the values for DLOCAL and DECO can be
approximated from the statistical frequencies of weight-limited
vehicles in GVW Class 8B (i e., those 3,276 trucks that met the
PCARWT greater than 75% criterion).

* Horsepower ratings under the uncapped Bridge Formula B scenario
increase by the same percentage as GVW for increasing axle
configurations.

Table 3-8 presents the average physical and operational characteristics for
these vehicle configurations under both the capped and uncapped Bridge Formula
B scenarios (LCV data is shown for later reference). Statistical analysis was
performed on weight-limited vehicles in Class 8B to determine the values for

Volumetric capacity restrictions are not relevant in the immediate
analysis since size limits remain constant But such restrictions are relevant
when comparing fuel productivity between LCVs and conventional configurations
Carriers that are currently transporting light density freight with Twin 28s will
be able to increase payload by shifting to LCVs that have longer trailers

3-26


LGPMg 7-1-5546 - 0.0112*(5.16) + 0.0426*(-1.1034) + 0.1113*(-0.0127)
+ 0.0255*(0.2540) - 0.0181*(0.2250) - 0.0275*(0 1590)
= -1.6628

where, MDLIDX = 5.16, LWIWGT3 = -1.1034, LHPCTR = -0.0127, DLOCAL = 25.4%,
DAERO = 22.5%, and DECO = 15.9% (see Table 3-6).

Taking the anti-log of -1.6628 gives 0.1896, or the estimate of average GPMg.
The inverse of 0.1896 defines MPG;, which in this case equals 5.2743.

The same Procedure can be used to estimate MPG, for GVW Class 8B under the
wrpwcT2 definition of vehicle weight. Using LWIWGT2 instead of LWIWGT3, and
assuming that all other variables remain constant, MPG, is estimated to be

5.0582.

Having estimated MPG, and MPGc, G,, can be calculated from Class 8B’s data in
Table 3-6- Simply, payload when empty mileage is not incurred equals 22.20
tons, Payload when empty mileage is incurred equals 15.18 tons. It follows
that fuel productivity is 112.29 ton-miles per gallon under no empty mileage

and 77,81 ton-miles per gallon with empty mileage. As a result, Gasp is
estimated at 44.31%.

This procedure was performed for each GVW class and engine type combination.
The results are presented in Table 3-7. It is clear that empty mileage has a
severe detrimental effect on fuel productivity. Avoiding empty mileage can
potentially increase fuel productivity by 33 to over 60 percent. However,
there ar@ many reasons why these increases will not be achieved. The ability
of a carrier to avoid empty mileage greatly depends on logistical and
managerial factors. First, a carrier may not have perfect information
regarding the availability of a load, and miss the opportunity to carry it
Even if perfect information exists, a carrier may choose to return empty
rather than wait for the next available load if time restrictions are a
concern. Second, irregular route, specific commodity carriers may never
encountet traffic for which a corresponding backhaul exists within the

constraints of commodity and point-to-point restrictions. Third, backhaul


pound saved basis. The high prices are, to a degree, a function of the
limited sales volume of these options. In general, neither Volvo nor Navistar
expected or had specific programs for (large) weight reduction through
material substitution, but expected 100 to 200 lbs in weight savings over the
next ten years. Volvo stated the weight reduction potential was 500 kg (1100
lbs) for the tractor, and up to 500 kg for the trailer for a Class 8B
combination truck. Volvo stated that Class 6/7 trucks had only a 200 kg
weight reduction potential. However, it was not clear that these potential

reduction levels could be obtained in a cost-effective manner.

Weight reduction by the use of lightweight engines of high specific output is
already occurring A detailed listing of engines by horsepower category and
their weights is provided in Table 4-3. The 350 to 450 HP range is unlikely
to see any major weight reduction except in certain specific cases, as, for
example, by replacement of the Mack EM-9 V-8 engine with six cylinder engines
Engines in the 350 to 450 HP range are widely used in the Class 8B truck
market by owner operators and fleet owners who need extra power to negotiate
the steep gradients in many Western states. The 290 to 350 HP range is more
commonly specified by fleets in Eastern states that are concerned about fuel
costs. In 1990/91 Caterpillar and Cummins introduced the so called ‘10 litre’
engines that weigh 1900 to 2050 lb with ratings of 300 to 350 HP The engines
can directly replace the popular Cummins NTC Series and Caterpillar 3406
engines, with a weight savings of 500 to 600 lbs. However, these engines have
only about 30 percent of the Class 8B market in 1991, but can be expected to
increase market share in the future. The 240 to 290 HP segment is usually
specified for 60,000 lb Class 8B trucks or by the ‘supermedium’ 50,000 1b
Class 8A trucks In this class, weight savings may be significant only 1f
owners choose the more traditional '’medium-duty’ engines such as the DTA466,
or high output versions of the Caterpillar 3116 These engines will have
lower durabilicy than.the L1OQ and 3176, and also have lower efficiency so that
the weight reduction will not be a major factor affecting fuel economy.
Similar concerns are valid for the 190-240 HP engines used in Class 7 and some

Class 8A trucks where moving from a Cummins C-series engine to a B-series may

4-11


forecast for the light-heavy duty class of trucks, a 3.6 percent for the
medium-duty class and a 4.8 percent improvement for the heavy-heavy-duty
class. Our analysis, described below, shows that the EMA projections are

relatively reasonable

As noted, engine bsfc improves with increasing the brake mean effective
pressure (bmep) of the engine since friction and pumping loss do not increase
in proportion to bmep, while output does. Some of the advantage of the newer,
small displacement engines is due to the increased BMEP. For example,
Caterpillar’s 3176 rated at 325 HP has a peak torque BMEP of 300 psi which is
10 to 15 percent more than the BMEP of the typical 14 litre engine, and it
displays one of the lowest bsfce ratings of all engines for which data was

obtained.

There are obvious structural and durability limits to the increases possible
in BMEP and Caterpillar believed that the 3176 had reached the limits of the
high BMEP strategy. Volvo and Mercedes were in general agreement that this
strategy produced some fuel economy benefit, but Cummins did not subscribe to
this view, as it believed its 14 litre and 10 litre engines had near identical

bsfce at the same rated HP.

Current thermodynamic efficiency of diesel engines is about 40% at the optimum
bsfc point. Volvo suggested the following improvements were possible to

current engines:
* improved charge air cooling,
* electronic control of engine timing,
* improved air utilization,
* adjustments to compression ratio, and
* variable geometry turbocharging

Air-to-air charge cooling is now (1991) available in virtually all heavy-duty
diesels except in the light-heavy category and further improvements to change
air cooling will result in very small benefits to fuel economy, probably less


‘VARIABLE

GEM

LGPM

MDLIDX

FRCLOAD

FRCNLOAD

EQUIVHT

WIDWGT1

LWTWGTL

WIDWGT2,

LWTWGT2

WIDWGT3

LWTWGT3

MIDCID
MEANCID
CIDCTR

LCIDCTR

MIDEP
MEANBP
BPCTR

LHPCTR

DLOCAL

DAERO

DECO

TABLE 3-4

DEFINITIONS OF EEA VARIABLES

DERTEETION
GPM = 1 / MPG
Defined as gallons-per-mile, the inverse of MPG

LGPM = In (GPM)
The natural log of GPM

MDLIDX = MODELYR - 1976
Defined as model year index whose range of possible values is 1 to 11

FRCLOAD = (100 - PNOLOD) / 100,
The fraction of annual mileage that the vehicle did carry a payload

FRCNLOAD = PNOLOD / 100
The fraction of annual mileage that the vehicle did not carry a payload

EQUIVWI = (AVWGHT x FRCLOAD) + (EMNGHT x FRCNLOAD)
The equivalent woight, or average operatang weight, of the vehicle accounting for empty
mileage

EEAMAX is defined as the high end of a vehicle's EEAGW range, expr
EEAMAX = 13 0 for vehicles in GVW Class 5

ed in tons

EEAMAX = 16 5 for vehicles in GVW Class 6
EEAMAX = 30 0 for vehicles in GVW Class 7
EEAMAX = 40 0 for vehicles in GVW Class &
EEAMAX © 70 0 for vehicles in 9

WIDWGT1 = EQUIVWT / EEAMAX
The equivalent weight of the vehicle, normalized to that vehicles weight class

LWTWGT1 = In (WIDKGT1)
The natural log of WTDWGT1

WIDWGT2 = AVWGHT / EEAMAX
The average weight of the vehicle, not accounting for empty mileage, normalized to thet
vehicle's weight class

LWIWGT2 = Ln (HTDWGT2)
The natural log of WIDWGT2

WIDWGT3 = EMWGHT / EEAMAX
The empty weight of the vehicle, normalized to that vehicle’s weight class

LWIWGT3 = ln (WIDWGT3)
The natural log of WIDWGT3

MIDCID 1s the midpoint of the reported CID range for a vehicle
MEANCID 1s the expected value, or moan, of the MIDCIDs for a give GVW class

CIDCTR = MIDCID / MEANCID
A vehicle's approximate engine size, normalized to that vehicle's weight class

LCIDCTR = ln (CIDCTR)
The natural log of CIDCTR

MIDHP 15 the midpoint of the reported HRSPWR range for a vehicle
MEANEP 1s the expected value, or mean, of the MIDEPs for a given EEAGVW class

HPCTR = MIDEP / MEANEP
A vehicle's approximate horsepower rating, normalized to that vehicle's weight class

LHPCTR = In (HPCTR)
The natural log of APCTR

DLOCAL 1s a dummy variable that equals 1 when AREAOP equals 2 and DLOCAL equals 0 if
AREAOP does not equal 2

DAERO 1s a dummy variable that equals 1 if AERODN equals 1 and DAERO equals 0 if AERODN
does not equal 1

DECO 1s a dummy variable thet equals 1 if ECOENG equals 1 and DECO equals 0 if ECOENG
does not equal 1

3-16


9-¥

‘CORRB

INTERCEP
MOLIDX
LATWGT 1
LPCTR
DLOCAL,
DAERO

MODEL 6

Dependent Variable: LGPM

--~ EEA GVW Group=33,000-60,000 Lbs Type of fuel used by vehicle-Diese?

Analyste of Variance

Haan
Source oF Square F Value Prab>P
Hoda 333 sBas2 & 79688 213.188 4 0001
Error Te AEE 60160  BbOOS
C Total 7775-300 $8702
Root MSE O 24505 R-square 0 0679
Dep Mean -1 70807 = Ad R-9q 0 0673
cv 14 98692
Parametex Estimet:
Parameter Standard T for RO-
Varieble OF Entimete Error Paremeter=0 = Prob > |T}
INTERCEP 1 -1 602002 © 00851730 ~288 068 0 0000
OLIDK 1 -0 O1N171 —-o 0ogBaRd “12 568 © 0002
teTWOTL 1 01743810 01225586 14 225 9 0001
LHPCTR 1 © 063006 9 o09a6a8s 6 389 9 0001
DLOCAL 1 © 050868 © 00611715 eae 0 0001
DAERO 1 -0 057297 0 00964660 -5 94a @ gaot
Correlation of Estine!
IRTERCEP MOLIDX LWTWGTS LHPCTR DLOCAL
1 co00 -0 4700 oO 6684 -0 0630 70.4481
-O 4700 1.0et0 -0 0625 0 1128 01175
© 6604 -O 0625 1 0000 -0 0361 0 0979
-0 0830 oO 4124 ~O 0381 1 0000 0.1675
<0 4483 0 2175 0 0979 0 1675 1 0000
0 1543 0 2512 -0 0628 -0 0517 B.1960

-0 1543
-0 2512
+0 0626
-0 0517
0 1960
1 0900


Table
Table
Table

Table
Table
Table

Table
Table
Table
Table
Table
Table

Table
Teble

Table

Table

Table

Table

2-21
2-2
2-3

3-1
3-2
3-3
3-4
3-5
3-6

3-7
3-3

3-9

3-11

3-12

LIST OF TABLES

Distribution of Trucks By Engine Type and GVW Class .

Sales and Diesel Penetrations By Class

Penetration Rates of Fuel Beonony Options By GVW Class and

Engine Type... . . . . :

Gasoline Trucks by Use and Body Style Percent By GVW Class
Diesel Trucks by Use and Body Style Percent by GVW Class
Percent of Trucks by Area of Operation By GVW Class and
Fuel Type . see ee eee toe

State Size Limits .

Interstate National Network Allowable Gross Weight
Definitions of TIUS Variables Used In The Analysis
Definitions of EEA Variables

Listing of Fitted Models

Statistical Means of Selected Variables By GVW Class and
Engine Type Combination . rn

The Effect of Empty Mileage on Fuel Productivity

Physicel and Operaticnal Sheracteristics of Weight-Limited

S-Axle or Greater Trucks

Estimates of Fuel Productivity Gains From Eliminating the
80,000 lb GVW Cap .

Typical Dimensions and Volumetric Capacities For 5-,
6-Axle Tractor-Semis, Twin 28s, an LCVs .

Physical and Operational Characteristics of Size-Limited
5-Axle or Greater Trucks

Fuel Productivity Estimates for Size-Limited Vehicles
and Potential Gains From Shifts to LCVs .

ii

2-10
2-12
2-13

2-16

3-8
3-9

3-14
3-16
3-19

3-21
3-23

3-27


The highway MPG improvement is as large as the one calculated for Class 8B
trucks, but the source of the improvement is quite different; in this case,
engine improvements are the main contributor. These engine improvements are
also available in the city cycle, and the net benefit at city speeds is also
quite large. The city/highway composite improvement is 21.4 percent, using a
weighting of 70 percent city/30 percent highway, without any emission penalty
and 18.5 percent if the penalty is as large as anticipated without any
breakthroughs in technology. This translates to an annual rate of growth of
1.3 percent, which is again in good agreement with the historic rate of growth

experienced in the 1978-1987 time frame.

In conclusion, it appears that technology is available to continue the
historic growth rates or even exceed them slightly with no government

intervention in the markets.


Nevertheless, there are measures that can be taken by trucking companies and

government to alleviate the impact of empty mileage. These measures are:

* The introduction of managerial and logistical techniques by
trucking companies that identify available loads and better
manage a carrier's route.

« A federal mandate that eliminates or relaxes backhaul
restrictions at the state level, which is expected to have a
disproportionate impact in larger states where carriers are
often forced to incur empty backhauls for many miles.

* Government sponsored clearinghouses that locate and inform
individual truckers about the availability of backhaul loads

The current 80,000 lbs GVW cap results in the inability of a carrier to use
some portion of the vehicle’s potential capacity by restricting the weight of
the items being shipped Payload capacity is determined by the difference
between the truck’s maximum practical GVW and it’s empty (or tare) weight
Carriers operating Class 8B trucks that haul high density freight are often
weight-limited by the 80,000 lbs GVW cap. The weight limit does not allow the
carrier to load the truck to its optimum density where weight and size
capacities are fully utilized Such foregone gapacity penalizes fuel

productivity and translates into an opportunity cost to the carrier.

A policy that eliminates the 80,000 lbs GVW cap, and limits GVW through axle-
load limits and Federal Bridge Formula B, will result in substantial increases
in the use of 6-axle tractor semitrailers and Twin 28s, as weight-limited
carriers shift away from 5-axle tractor-semitrailers to these configurations
to take advantage of higher fuel productivity. This higher productivity
results because axle-weight limits constrain the maximum practical GVW of 5-
axle tractor-semitrailers to 80,000 lbs even under an uncapped Bridge Formula
Boscenarieo On the other hand, 6-axle tractor-semitrailers and Twin 28s would
be allowed to operate beyond 80,000 lbs under Bridge Formula B and current
axle-load limits if the GVW cap is lifted. Payload gains of shifting to these
configurations are expected to be greater than the empty weight penalties that

these heavier configurations impose.


computerized their operations. Such a program would be cost effective if a
fee structure is designed that is economical to users and a revenue source to

government.

3.5 FUEL PRODUCTIVITY UNDER AN UNCAPPED BRIDGE FORMULA B

This section quantifies fuel productivity gains from eliminating the 80,000
lbs GVW cap. Under this scenario, GVW would be controlled by existing axle-
weight limits and by Bridge Formula B. As was shown in Section 3.2, allowable
GVWs under the Bridge Formula are determined by the number of axles on a
vehicle and the distance between the extremes of any group of 2 or more axles.
Eliminating the 80,000 lbs GVW cap would not affect conventional 5-axle
tractor-semitrailers, since these configurations cannot exceed 80,000 lbs
without violating current axle-weight limits However, 6-axle tractor-
semitrailers and Twin 28s would be directly affected by this policy. Under
the uncapped Bridge Formula B scenario, 6-axle tractor-semitrailers would
typically be allowed to operate at 86,000 lbs GVW, while 5-axle Twin 28s would
be allowed to ‘gross-out’ at 91,500 lbs. Seven-axle, 8-axle, and 9-axle Twin
28s would be allowed to operate, without special permit, at 99,500 lbs,
104,500 lbs, and 110,000 lbs, respectively. The analysis assumes that no
changes in state length limits will take place, and fuel productivity
calculations are based on 48 ft semitrailers for tractor-semitrailer
configurations and 28 ft trailers for double trailer configurations to assure
that the benefits reflect nationwide operation. The nationwide operation of
LCVs will not be affected. By definition these configurations are double
trailers that have at least one trailer longer than 28 ft violating most
states’ Length limits (see Table 3-1). The fuel productivity benefits of LCVs
are recognized later in the section through fuel productivity comparisons with
5-axle, 6-axle tractor-semitrailers and Twin 28s operating under the uncapped

Bridge Formula 8 scenario.

Fuel productivity changes resulting from the elimination of the 80,000 lbs GVW
cap can be estimated by employing the regression model for GVW Glass 8B that
is specified in Section 3 3 Because GVW Classes 6, 7, and 8A do not include

5-axle or greater vehicle configurations, trucks in these classes are not

3-25


on the EPA test cycle significantly, However, the principal benefits of the
electronic systems are associated with:

* shaping of the torque curve to allow drivers to operate at
lower RPM in top gear,

* gear shift indications,

* road speed governor functions,

* engine shutdown and protection systems,
* extended idle shutoff,

¢ driver monitoring,

¢ and engine/vehicle diagnostics.

An example of such an electronic system is Mack Trucks’ VMAC computer control
system. The system is optional at a cost of $3000, and is available for

Mack's Class 8B trucks.

The benefits of the system are dependent on the baseline. If a driver
maintains speeds at or below legal limits and selects the appropriate gear for
cruise, the system provides benefits only from torque curve shaping. Larger
benefits will be obtained relative to the average driver who may be
overspeeding on the highway. Proper shifting during city driving can also
save fuel, and shutting the engine off rather than subjecting it to extended
idle will also save fuel. These benefits are difficult to estimate as there
are no detailed analysis of current inefficiencies in driver behavior that are
publicly available. Estimates of fleet average impacts are largely based on

anecdotal evidence, and not though any actual analysis.

Benefits were estimated by industry experts for electronic injection timing
shaping the torque rise of the engine, speed control to 65 mph, shift control

and extended idle shutdown. Total benefits are as follows:

City Highway
Class 6/7/8A 30 5.0
Class 8B 2.5 60


€2-%

6.00

FIGURE 2-10
Average MPG By Vintage
GVW Class 8A Diesel Trucks

6.75

6.50

Qv=

5.25

5.00 |—+- t

1977 1978

Model Year 1977 includes 1977 and
pre-1977 models

1979 1980 1981 1982 1983 1984 1985 1986 1987
Model Year


61-2

FIGURE 2-6
Average MPG By Vintage
GVW Class 7 Gasoline Trucks

7.60

2

650 - -- ~~

en

Qv=S

6.60 pepe

5.00 --~ — nt ee

1977 «1978 1979 1980 1981 1982 1983 1984 1985 1986 1987
Model Year

Model Year 1977 Includes 1977 and
pre-1977 models


TABLE 4-8
IMPROVEMENTS TO CLASS 6/7

TRUCKS, 1987 - 2001

Technology Market City F/E Highway F/E
ene tion Inc:
Weight Reduction 100 0.35 0.15
Drag Reduction: Van Body 45 0.15 3.35
Other 35 0.07 1.69
Rolling Resistance 45 0.90 135
Engine Improvements” 100 12.00 12.00
Drivetrain Optimization 100 2 00 2.00
Electronic Control 100 3.00 5 00
Lubricants 100 1.00 05
19 47 26 04
Potential Effect of NO, Standards. (-2 5) (-4 00)

*

Weighted for light-heavy diesels in Class 6


interstate highway system.” The federal regulation on length imposes a
minimum criterion on a state’s maximum length regulation. States must permit
these lengths, but can set limits on semitrailer and double trailer lengths
beyond 48 ft and 28 ft, respectively (see Table 3-1). These state maximun
length limits are important because in the absence of the 80,000 lbs GVW cap,
Bridge Formula B would allow higher GVW limits depending on the number of
axles and the distance between the extremes of any two or more consecutive

axles, assuming that axle-weight limits are met.

Permissible gross weights under Bridge Formula B are shown in Table 3-2. This
table demonstrates that the maximum allowable GVW for a 2-axle truck is 40,000
lbs providing that the distance between the axles is 10 ft. For a 3-axle
truck the GVW limit under this formula is 60,000 lbs providing that the
distance between the extreme axles is 32 ft. A 4-axle truck combination can
reach an overall weight of 80,000 lbs only when the distance between the
vehicle’s extreme axles is not less than 57 ft. However, even if distances
are satisfied, these configurations will not reach the Bridge Formula B GVW
maximums because axle-load limits will rarely be met This means that the
maximum practical GVW for these truck configurations is actually determined by
the axle-weight limits that are discussed above. Under these axle-weight
Limits, a 2-axle truck with a 12,000 lbs load on the steering axle and a
20,000 lbs load on the rear single-axle has a practical GVW limit of 32,000
lbs. A 3-axle truck with two single-axles and 12,000 lbs on the steering axle
has a GW limit of 52,000 lbs, while a 4-axle truck with one single-axle, one
tandem-axle, and 12,000 lbs on the steering axle is Limited to 66,000 lbs GW.
Likewise, a typical 5-axle tractor-semitrailer with two tandem-axles and
12,000 1bs on the steering axle is limited to a practical GVW of 80,000 lbs by
the axle-weight limits, although Bridge Formula B allows for higher GVWs as

the distance between extreme axles increases.

* STAA of 1982 also required states to allow use of combinations consisting
of a tractor and two trailing units on the interstates and the network of primary
roads .?

3-7


MDDEL 8
Dependent Variable LGPM

EEA GVW Group-Over 60,000 lbs Type of fuel used by vehicle=Diesol USETYPE=1 --

Analysis of Variance

Sum of Mean
Source oF Squares Square F Value Prob>F
Model 4 1 20481 © 30120 10 398 0 0001
Error $51 15 96073 © 02897
C Total 555 17 16556
Root MSE 0 17020 0 0702
Dep tHean -2 59473 0 0635
cv -11 08968
Parameter Estimates
Parameter Standard —T for HO
Variable DF Estimate Error Parameter=0 = Prob > {T|
INTERCEP 1 -1 431978 0 02528792 -36 627 0 0001
MDLIDX 1 0 009221 0 00216618 4257 0 0001
LWIWGT1 1 0 061648 © 02673900 2 306 0 0215
LHECTR 1 0 148885 0 04555618 3 268 0 0011
DECO a -0 059064 002693986 -2 192 © 0288
Correlation of Estimates
CORRE INTERCEP MDLIDX LwTwer1 LHPCTR DECO
INTERCEP 1 0000 -0 5083 0 8567 0 0091 0 0312
MDLIDX 0 5083 1 0000 0 1071 ~0 0817 -0 2626
LwwcT1 0 8567 -0 1071 1 0000 -0 0761 0 0076
LHECTR 0 0091 -0 0617 0 0781 1 0000 0 0312

DECO 0 0312 0 2626 0.0076 -0 0312 1 0000


in those Models for lighter truck classes, suggesting that operating weight
has less of an impact on the fuel consumption of Class 8B trucks than on the
fuel consumption of trucks in lighter GVW classes. From an engineering
standpoint, however, the effect of operating weight should be much higher
(approximately 0.30) than the estimated value (0.0426), since this effect is
expected to increases as the weight of the vehicle increases. EEA has
conducted extensive analysis to identify inconsistencies inherent in the data,
but must conclude that other unidentifiable compensating effects are driving
Class 8B‘ s LWIWGT1 coefficient to such a low level. With this caveat in mind,
EEA is confident that the analysis does provide reliable estimates of

potential fuel productivity gains from eliminating the 80,000 lbs GVW cap.

The Fuel Productivity of LCVs

Under assumptions made in this study, the nationwide operation of LCVs would
not be affected by the elimination of the 80,000 lbs GVW cap because LCVs have
longer trailer units that violate most state length limits. However, in those
states where length restrictions allow their operation, carriers operating
both size and weight-limited loads will benefit by shifting to LCVs when the
80,000 lbs GWW cap is lifted and permits are not required for their operation.
This section characterizes the fuel productivity of Rocky Mountain Doubles and
Turnpike Doubles through comparisons with 5-axle, 6-axle tractor-semitrailers

and Twin 28s operating under the uncapped Bridge Formula B scenario.

In those states where length restrictions do not prohibit the operation of
Rocky Mountain Doubles and Turnpike Doubles, lifting the 80,000 lbs GVW cap
will affect carriers operating weight-limited Twin 28s and carriers operating
size-limited 5-, 6-axle tractor-semitrailers or Twin 28s. As shown earlier in
Section 3.5, weight-limited operators of 5- and 6-axle tractor-semitrailers
benefit by shifting their operations to Twin 28s, Weight-limited carriers
operating Twin 28s, on the other hand, can gain by shifting their operations
to Rocky Mountain and Turnpike Doubles since these LCVs have longer distances
between extreme axles and are thus allowed higher GVWs under Bridge Formula 8.

Size-limited carriers operating either 5-, 6-axle tractor-semitrailers or Twin


>
1
wa

ANTERCEP
MDL 1OX

Lerpcrr
LOCAL

EEA GYM Group=33,000-60,000 lbs Type of fuel used by vehicle-Gesoline

Source

Model
Ercac
C Yotal

Root HSE
Dep Mean
cv

Verteble OF

INTERCEP
wOLIDt
DatwoTs
LcIocTR:
DLOCAL

reer

INTERCEP

1 0080
-0 3066
0 33548
-0 1225
-0 S635

MODEL 5
Dependent Variable: LGPH

Analyste of Vartance

Sum of Mean
oF Squares Square
s 6 33916 1 38479
1639 150 66161 @ ave
1643-15? 00096
030319 = R-aquare
-1 60008 A
“18 94826

Porometer Estimates

Parameter
Eatiaete

-1-518736
-0 010200
oO 1agzes
@ 572893
0.081550

F Value Prob>F
17 240 0 0003
0 o404
0 0380

Standard = T for RO-
Evror Parameter=¢

03343680
9398089
03673395
99850945
02234609

Correlation of Estimates

MDLIOx

-0 3066
1 ooag
-0 0898
0 opag
© 06e3

LeTacT1

7338
-0 0496
1 oaco
-0 1552
0 0453

45 403
“2 562
3833
3

6
1 639

Prob > | tf

9 9008
9 0103
0 on01
0 coon
0 0632

70.5835
0 qeas
0 asa

-0 gos2
1 cope


Lastly, accessory drive losses for engines equipped with a variable fan drive
are typically in the 4 to 6 percent range for medium duty trucks, and somewhat
lower (3 to 5 percent) range for Class 8B trucks. Truck manufacturers suggest

that variable fan drives are used in over 90 percent of diesel engine powered

trucks.

4.3 WEIGHT REDUCTION

Weight geduction measures are actively being undertaken by truck manufacturers
in both medium-duty and heavy-duty truck classes. In most cases, the weight

reduction is largely due to two specific reasons:

e the substitution of plastic and aluminum components for steel
components

« the use of more modern, high BMEP engines that weigh much less
than older engines of the same power rating.

Weight reduction by material substitution has been widely introduced by all
major manufacturers in the last three or four years The cab (for non-sleeper
type cabs) is generally a common design used across all trucks from Class 5 to
8B, and Plastic hoods and fenders have been introduced by Freightliner,
Paccar, and Ford. For example, Ford uses a Reaction Injection Molded (RIM)
hood in their new Aeromax trucks. The items are considered ta be cost-effec-
tive pased only on production cost and have been introduced regardless of the
fuel savings potential. Aluminum is, however, a relatively expensive option
The aluminum Association has conducted a study of weight savings in certain
load pearing parts as shown in Table 4-2, and this study indicates a weight
saving of up to 900 lbs on a Class 8 tractor Currently, none of these parts
are made from aluminum, although Navistar offers special truck models with
aluminum frame rails as an option. The estimates in Table 4-2 may be

optimistic, as is the usual case with supplier provided data.

Navister, however, does offer an aluminum cab that offers a weight saving of
160 to 200 lb over a steel cab, depending on the model The cost for this
option is about $2000, equivalent to $10 to $12 per pound saved Navistar

indicated that aluminum frame rails were appropriately the same cost as a per

4-9


3. OPERATIONAL FACTORS TO
IMPROVE FUEL EFFICIENCY

3.1 INTRODUCTION

Transportation facilitates the exchange of goods and services. For a given
level of freight transportation demand, many combinations of the capital stock
and modal share (truck, ship, or airplane) can be used to satisfy that level
of demand. Each vehicle type within a mode has an average energy efficiency
(BTUs per vehicle mile), a characteristic load factor (freight ton-mile per
vehicle mile), and intensity of use (vehicle miles traveled per year).
Therefore, given a level of demand, energy conservation in transporting
freight by truck can be accomplished by reducing the energy input through
operational and technological improvements, and/or by increasing the number of
freight ton-miles traveled per unit of energy that is consumed (i.e.,
increasing fuel productivity) This section of the report provides a

quantitative description of the factors that influence fuel productivity

Fuel productivity in the movement of freight by truck largely depends on the
type of truck that is being used. Each vehicle type has physical and
operational characteristics that are unique. Typical vehicle types are shown
in Figure 3-1. Straight trucks are vehicles with the cargo body and tractor
mounted on the same chassis and usually consist of 2-, 3-, or 4-axle
configurations. Two-axle straight trucks are most often used in urban areas
where maneuverability is important and operate between 19,500 lbs and 33,000
lbs gross vehicle weight (GVW). Three and 4-axle straight trucks are
principally used in construction or other ‘rough-ducy’ uses Combination
trucks are vehicles that have a power unit (tractor) that is separate from the
trailer(s), and are generally used for interstate freight movement. Although
combination trucks may have 3 to 9 axles, the most common types are 5-axle
combinations with one 48 ft long semi-trailer and 5-axle double trailer
combinations with two 28 ft trailers (ie , 5-axle Twin 28s). Five-, 6-axle

tractor semitrailers, and 5-axle Twin 2Bs commonly operate between 60,000 ibs

3-1


Conversion to DI

10% Governed speed
reduction

High BMEP design

Improved turbocharger
matching

Air-to-Air
intercooling

Improved Thermodynamic
efficiency

Friction reduction
Pumping loss reduction
Total bsfc Benefit

Effect of 5.0 NO, Std.

Effect of 1998 NO, Std.

TABLE 4-6

IMPROVEMENTS TO ENGINE
BSFC, 1987-2001

Light-Heavy
Mkt. P. E Ga
80 12.0
80 4.0
(0) 0
80 8.0"
100 5.0
100 10
100 1.5
100 1.0
325
0
-3.0 to -5.0

* Conversion from naturally aspirated.

Medium-Heavy

50
50

100

80

100
100

100

-3.0 to -5.0

Heavy -Heavy
en, F/E Gain Mkt, Pe F/E Gain

20

80

100

30

100

100

20

-3 0 to -5.0


GVW Class

Class

Class

Class

Class

Class

Buses

5

6

BA

8B

TABLE 2-2

SALES AND DIESEL PENETRATIONS

BY CLASS
1980 1990

Sales % Diesel Sales % Diesel
1,860 - 1,726 -
51,170 24.4 17, 687 71°05
54,360 62.2 61,010 81.55
10,400 74.5 11,981 99 70
93,490 100.0 122,181 100.0

- - 32,731 78.2


WEIGHT SAVINGS FOR SPECIFIC ALUMINUM PARTS

Part

Front Bumper

Front and Rear Hubs

Front Wheels

Drive Axle Wheels

Rear Axle Carrier Housing
Rear Axle Carrier Housing
Rear Axle Carrier Housing
Frame Rails

Fuel Tank (100 gallons)

Air starter with aluminum air

reservoir

TABLE 4-2

Weight Sav:

37
220
22
90
71
110
131
200
30

47

Vehicle

Lbs


Additional advances in rolling resistance reduction will come about from
improved rubber formulations, new tire cord materials and the development of
new tread designs. Based on confidential data received from the manufactur-
ers, Navistar estimated that rolling resistance reduction of 20 to 25 percent
was possible for tractor tires in the Class 8B long haul trucks For trailer
tires, or non-traction tires, they estimate a reduction in the range of 10
percent. The 10 percent figure was also estimated as likely for medium duty
truck applications. Some tires have already shown significantly greater
reductions already, but these tires have compromised durability and/or
handling properties, For example, Continental sold a special tire in the
European market that had a 28 percent reduction in rolling resistance co-
efficient in comparison to a similarly sized standard tire, but had to
discontinue sales due to problems with heat buildup. Future improvements are,

however, not expected to impact durability.

The tread depth and number of wheels also impact tire rolling resistance.
Tire rolling resistance has been found to vary inversely with tread depth;
many special fuel economy prototypes often used ‘shaved’ tires to maximize
fuel economy. Hence, special snow tires or traction tires tend to have
significantly higher rolling resistance compared to standard tires. Volvo
also found that the increasing number of wheels increases total tire rolling
resistance. Data for a 78,000 lb GVW tractor-trailer, shown in Figure 4-2,
suggests that increasing the number of wheels from 18 to 26 decreased fuel
economy by one percent. The popular Class 8B tractor-trailer typically uses
18 tires, and some tire manufacturers have sought to replace the 4 tires on
each of 4 axles with 2 tires, called ‘super single’ tires, with significant
improvements in fuel economy. However this has not been popular since a tire
blowout causes an unacceptable loss in payload capacity and driveability In
Europe, where three axle trailers are more common, the super single tire has
received greater acceptance. Manufacturers do not foresee substantial

increases in market penetration for super single tires to 2001 in the U.S..

4-16


efficiency. Technological innovations influence truck classes differently,
while policy may only affect a certain subset of the heavy-duty truck fleet.
It is, therefore, important to characterize the physical and operational
characteristics of each GVW class independently. Section 2.2 describes data
used in this analysis. Section 2.3 describes physical and operational

characteristics of the heavy-duty truck fleet.

2.2 DATA USED IN THE ANALYSIS

This study uses data from the 1987 Truck Inventory and Use Survey (TIUS) The
TIUS is conducted every five years by the Bureau of Census, and is the only
publicly available survey providing data on the physical and operational
characteristics of the nation's truck population. It is based on a
probability sample of private and commercial trucks registered in each state
during 1987. However, vehicles which are owned by federal, state and local
governments are excluded from the sample universe, as well as ambulances,

buses, motor homes, and farm tractors.

The TIUS data base consists of 104,606 records and approximately 200 variables
that describe the characteristics of each truck in the sample universe. To
assure that the analysis recognizes differences between physical and
operational characteristics across the in-use truck fleet, EEA devised a data
clean-up and accuracy check routine. This routine classified each truck to

its corresponding industry weight class

The TIUS data clean-up process involved three steps. First, some trucks were
re-assigned to different GVW classes A preliminary screening of the data
revealed that a number of trucks reported maximum loads well outside the
appropriate range of the TIUS assigned GVW category A set of re-
classification rules were developed to re-assign these vehicles to the correct
category. These rules were based on available information regarding a truck's
make, fuel type, fuel economy, engine size, horsepower, number of cylinders,
and maximum loaded weaght. A total of 7,212 trucks were assigned to different
GVW categories on the basis of these rules Second, engine and performance

parameters were compared for each truck to the expected range of values for

2-2


9-0

CORRB

INTERCEP
MDL IDX
LWTWGT1
LHPCTR

DAERO

MODEL 4

Dependent Variable: LCPM

=> EEA G¥W Group=26,000-33,000 lbs Type of [uel used by vehicle-Diesel ---

Analysis of Variance

Sum of Heen
Source oF Squar Square F value Prob>F
Model 5 28 90499 3 78100 a7 187 © 0001
Ercor 1980 129 29585 0 06631
Cc Total 1955 138. 20086
Roat MSE 0 25750 R-aquare 0 1827
Dep Kean 7-1 93861 Adj R-8q o 6
cv -13 26129
Parameter Estimates
Paremeter Stonderd T for 60
Varieble DF Estincte Ecrot Peremeter~0 = Prob > [T|
INTERCEP 1 -1 743511 (0 01716069 -101 399 © 0090
HOLIDX 1 -0 030025 0 00169165 -17- 749 © 0001
LWTWGTi 1 0 233573 0 03138824 7 401 © oo01
LHECTR 1 0 093002 = 0 05222425 ayer 0 0751
DLOCAL i © 063468 © 01246407 3 092 © 00013
DAERO a 0 041537 0 02278766 -1 623 0.0685
Correlation of Estinat.
INTERCEP MDLIDX LWTWGT1 LBPCTA DLOCAL
1 0000 -0 6271 0 5361 -0 0377 ~0 $342
-0 6271 1 o000 0 0712 0 3390 Oo 1153
0 5381 -0 0712 1 9000 0 0174 @ 0997
-O 0377 @ 1390 oO oa 1 0000 0 0229
-0 5342 @ 1155 0 0337 0 0229 1.0000
-0 1007 -0 1037 -0 0320 -0 0158 0.0940

-0 1007
0.1037
-@ 0320

0 0940
2 0000


specific drag reduction from the basic cabs (which are already lower drag

designs) are as follows:

9600 7100
Cab roof fairings 12% 10%
Side fairings 3.5% 3.7%
Roof and Side fairings 13.5% 19%
Full roof and side fairings 18% N/A

Typically, the full roof and side fairing ‘aero package’ costs $1400 to $1500
for trucks without sleeper cabs, and about $2300 for trucks with a sleeper
cab. Navistar offers a highly aerodynamic 8300 cabover model that, when
equipped with the same aero package, is about 10 percent more efficient than
the 9600 and 7100 models listed above. In general, these drag reductions are

typical for industry average and special ‘aerodynamic’ trucks, respectively

Potential for further improvements in Class 8B truck aerodynamics exist
Navistar has displayed a prototype truck called ‘IDEA’ that has 15 percent
lower drag than the current best truck (the 830€ series). Navistar identified
the potential for drag improvements in the tractor alone of up to 25 percent,
while an integrated tractor-trailer can nave the potential for up to a 40
percent reduction over the current new truck fleet average. However, many of
the features required, such as tractor-trailer gap seals, tractor skirts and
rounded van corners are not popular due to the payload reduction potential
incurred, as well as the lack of flexibility in switching tractors to differ-
ent trailers. Volvo agreed with Navistar’s assessment, and believed that
tractor related reductions are more likely to be realized by 2001. Navistar
suggested that a 15 to 20 percent additional drag reduction would occur due to
market forces by 2001, These values refer only to Class 8B trucks with van
bodies, which account for about % of sales. In other truck types such as
flat-beds, stake-beds, livestock haulers, petroleum tankers, etc., drag

reductions are likely to be in the 7 to 10 percent range.

Smaller reductions in drag are forecast for medium duty trucks. Currently,

most medium duty trucks do not even feature rounded corners for the van body


Appendix A

Statistical Results of the
Regression Models to Estimate GPM


by 5.2 HP (or about 10 percent). Some of the changes are inappropriate for
turbocharged engines, such as the 2-ring piston. Other friction reduction
technologies include roller-cam followers, that are widely used in most
domestic engines, but can be adopted for some medium duty engines, and
improvements to the fit and shape of the piston and cylinder liner by improved
manufacturing technologies. Most of the manufacturers interviewed for this
study suggested that 5 percent reduction in friction was likely by 2001, while
a 10 percent change was the highest conceivable limit of friction reduction.
A 5 percent reduction in friction translates into a 0.75 to 1 percent fuel

economy benefit averaged over a range of load/speed conditions

Friction increases rapidly with engine RPM, and 10 percent decrease in RPM
will bring about a proportionally larger reduction in friction, as the
dependence is non-linear. Most heavy-heavy duty engines already operate in
the 1800-1900 RPM range, although models rated to 2100 RPM are still avail-
able. Models rated at 1600 RPM as special “economy” models have been avail-
able since the early 1980's but have not been very popular since the drive-
ability of these engines saves fuel both by friction reduction and by limiting
truck speed. The new electronic controls in most engines make the 1600 RPM
engine redundant, as these new engines shape the torque curve to permit the
driver to cruise at 1500 RPM, while retaining the benefits of an 1800 RPM

engine during acceleration or in city traffic.

In the medium-duty applications, ratings at 2800 RPM or 2600 RPM were
traditionally popular, but new models rated at 2300 RPM or 2400 RPM have
become available in the last few years. These models have higher torque than
their 2600/2800 RPM counterparts, and require transmissions and axles with
higher ratings. The lack of availability and increased cost of transmissions
and axles has held back the market penetration of these lower RPM rated
engines Electronic controls have not yet been adopted, and are likely to
increase penetration in the future Reductions in the peak RPM to 2300/2400
RPM from 2600 RPM can result in fuel economy increases of 3 to 4 percent with

no change in vehicle speed.


TABLE 3-10
TYPICAL DIMENSIONS AND VOLUMETRIC CAPACITIES

FOR 5-, 6-AXLE TRACTOR-SEMIS, TWIN 28s, AND LCVs

5-Axle 6-Axle 5-Axle 7-Axle 8-Axle 9-Axle 7-Axle
Semi. Semi. Twin 28 Twin 28 Twin 28 Twin 28 LCV
Trailer(s) Width (in) 102 102 102 102 102 102 102
Trailer(s) Height! (ft) 135 13.5 13.5 135 135 13.5 145
Trailer(s) Total Length
(£t) 48.0 48 0 56 0 56.0 56.0 56.0 76.0
Estimated Volumetric
Capacity (cubic ft) 5,508 5,508 6,426 6,426 6,426 6,426 9,367

1 Most states limit the maximum height of the trailer(s) on tractor-semis
and Twin 28s to 13 1/2 feet However, LCVs usually are allowed to pull
trailers that are 14 1/2 feet high

9-Axle
Lev

102
14.5

96.0

11,832


TABLE 3-9

ESTIMATES OF FUEL PRODUCTIVITY GAINS

FROM ELIMINATING THE 80,000 1b GVW CAP

Fuel Productivity?

Fuel Productivity? Under Uncapped
Truck Configuration Under 80,000 1b GVW Cap Bridge Formula B
5-Axle Tractor-Semis 142.86 142 86
6-Axle Tractor-Semis 138.83 153.29
5-Axle Twin 28s 134.27 161.76
7-Axle Twin 28s NA 169 61
8-Axle Twin 28s NA 174.74
9-Axle Twin 28s NA 181 07

Ton-miles Per Gallon

NA: Not applicable since these configurations seldom, if ever,
operate below 80,001 lbs.


ST-Z

50%

40%

30%

20%

10%

0%

FIGURE 2-3

Average Percentage of Annual Mileage
When No Load Was Carried, By GVW Class

Average PNOLOD

Class 8A

GVW Class

WM Gasoline

Diesel



carries a typical load, since it reflects a vehicle’s operating weight when

carrying cargo.

The potential gain in fuel productivity from eliminating empty mileage is

calculated as follows:

Gy - MPG. x [AVWGET - EMWGHT) - 1) x 100
((FRCLOAD x MPG.) + (FRCNLOAD x MPG,)] x [EQUIVWT - EMNGHT)
where ,
Gis ~ Percent gain in fuel productivity for the average fuel type

j truck in class i,
MPG, = Estimated MPG when carrying cargo,
MPG, = Estimated MPG when operating empty.

Payload when no empty mileage is incurred on an average trip is given by
{AVWGHT - EMWGHT], and payload when some empty mileage is incurred is given by
(EQUIVWIT - EMWGHT]. Therefore, the numerator of the expression in parenthesis

represents fuel productivity when empty mileage is not incurred in a given

trip, while the denominator represents fuel productivity when some empty

mileage is incurred.

Before MPG can be estimated under either definition, it is first necessary to
determine the appropriate values for all the variables in a corresponding
regression model Table 3-6 presents the statistical means by GVW class and
engine type combination for some of the variables that were discussed in
Section 3.3. These means can be interpreted as the average characteristics of
a typical truck in a GVW class and engine type combination The mean for each
regression variable can, therefore, be plugged into the corresponding model to
estimate GPM, and GPMc. For example, average GPM; for GVW Class 8B is
calculated from Model 7 in Table 3-5 as:

3-20


restrictions at the state level may not allow certain carriers to avoid empty
mileage. Currently, approximately 30 states have economic regulations that
prohibit intra-state backhauls For example, a carrier originating in Chicago
with destination to San Antonio is not allowed (under Texas law) to transport
a load from San Antonio to Houston on his/her return to Chicago. Such
restrictions are of particular significance in larger states Finally,
backhaul restrictions stemming from the "Garbage Bill" limit some carrier's
ability to minimize empty backhauls. The "Garbage Bill" does not, for
example, allow carriers who haul food produce in one direction to haul
hazardous waste in the other For these reasons only a fraction of the

potential benefit from eliminating empty mileage will be recoverable.

Trucking companies can alleviate the detrimental effects of empty mileage by
introducing managerial and logistical techniques that identify available loads
and better manage a carrier‘s route. For example, innovation has led some
firms to find market niches where empty mileage can be minimized, while
computerization has allowed managers to better coordinate routes and identify
available loads Individual truckers, on the other hand, may not be able to
implement innovative management processes or computerize their operations
because of cost constraints and practical reasons. These truckers are
specially hurt by empty mileage since fuel costs often account for a large
portion of their total cost. Individual trucking practices are usually one-
man operations that operate at small profit margins and cannot incur the

additional cost of computerization or innovation.

From a policy perspective, a federal mandate that eliminates or relaxes
backhaul restrictions at the state level may prove worthwhile Such a policy
is likely to have a significant impact in large states, like Texas and
California, where distances between markets are greater and trucks are often
forced to incur empty backhauls for many miles Also, government sponsored
clearinghouses that locate and inform individual truckers on an on-time basis
about the availability of backhaul loads may prove to be helpful in
eliminating the information problem. These clearinghouses would specifically

help individual truckers and small trucking companies that have not

3-24


be impractical due to the reduced durability. The Caterpillar 3116 and the
Cummins C series engines are replacing the older Navistar DT466 and
Caterpillar 3208 models in the medium-duty Class 6 and 7 trucks, In the lower
than 190 HP engine range used in Class 6, trucks can shift to some of the new
light-heavy-duty engines such as the Cummins BT 5.9 litre, also with some loss
in durability. On a class average basis, industry experts anticipate that
engine changes (from the 1987 baseline) will contribute to the following
weight reduction by class:

« Class 8B - 250 lbs
« Class 8A - 200 lbs
* Class 7/6 - 150 lbs

The reductions are in addition to the reductions forecasted for material

substitution.

4.4 AERODYNAMIC DRAG

Aerodynamic drag coefficients of heavy-duty trucks for a tractor trailer
combination are usually quite high, historically, the drag coefficient (Cp)
has been in the 0.75 to 0.8 range While the simple wind deflector mounted on
the cab roof or the trailer nose cone has been available since the late-
1970's, more modern integrated cab/roof fairing designs have become available
from many manufacturers in the mid-to-late 1980's. The new aerodynamic cabs
were pioneered by Kenworth, and most manufacturers have since followed suit.
New models in Navistar‘’s popular 9000 series (Class 8B) have 30 percent lower
drag than the earlier trucks of 1980-1985 vintage when equipped with the full
aerodynamic package and a 102 ft trailer. In the medium-duty segment,
Navistar has also introduced more aerodynamic cabs that have 7 to 12 percent

lower drag, mostly from the change in the shape of the hood.

Navistar's simulation handbook provides a guide to the relative changes in
drag coefficients achieved by the different aerodynamic devices in a Class 8B
tractor trailer combination. The 9600 series is a ‘cabover’ design while the

7100 is a conventional tractor, and with a high van trailer, the device

4-13


GVW Class/Engine
Type
Class 6 Gasoline
Class 6 Diesel
Class 7 Gasoline
Class 7 Diesel
Class 8A Gasoline
Class 8A Diesel

Class 8B Diesel

TABLE 2-3

PENETRATION RATES OF FUEL ECONOMY OPTIONS
BY GVW CLASS AND ENGINE TYPE

% With

% With % With Fuel Variable % With
Aero Efficient Fan Radial

Devices Engines Drives Tires
1.0 O.1 0.0 0.1
6.3 2.8 0.5 1.3
14 0.8 O.1 0.3
6.4 3.0 lL. 1.5
0.9 0.2 0.0 0.0
9.8 5 6 1.4 27
22.5 15.9 4.3 73

2-10

% With

Fuel Max

Ratios
0.4
3.7
Li.
36
0.5

6.2


DLOCAL and DECO. The horsepower control variable for the uncapped Bridge
Formula B scenario (LHPCTR,) was scaled according to the percentage change in
GVW between increasing axle configurations. Typical empty weights for
different configurations were determined from conversations with staff at Jack
Faucett Associates and the American Trucking Association, and reflect tractors
pulling dry vans. The numbers for GVW under the uncapped Bridge Formula B are

oer

those that were derived in Section 3.2. Average operating GVW under the
80,000 lbs cap for 5-, 6-axle tractor-semitrailers and S-axle Twin 28s is
assumed to be 80,000 lbs since the analysis reflects weight-limited vehicles.
For 7-axle, 8-axle, and 9-axle Twin 28s, GVW under the 80,000 lbs cap has no
practical meaning, since these configurations seldom, if ever, operate below

80,001 lbs.

Having established the typical physical and operational characteristics of
these vehicle configurations, fuel productivity estimates can be derived for
both scenarios Regression Model 7 was used to calculate GPM under both GVW
scenarios and, together with payloads in Table 3-8, fuel productivity
estimates were derived Table 3-9 demonstrates the results of the
calculations. In practice, most weight-limited carriers facing an 80,000 lbs
GVW limit operate 5-axle tractor-semitrailers This is supported by the
estimates in Table 3-9, which indicate that weight-limited operations of other
than 5-axle tractor-semitrailers result in fuel productivity losses to the
carrier. Higher empty weights of 6-axle tractor-semitrailers and 5-axle Twin

28s allow less payload to be carried when GVW is limited to 80,000 lbs.

In contrast, when the 80,000 lbs GVW cap is eliminated, Table 3-9 shows that
the least productive configuration is a conventional 5-axle tractor-
semitrailer, Lifting the GVW cap will result in substantial increases in the
use of 6-axle tractor-semitrailers and Twin 28s, as weight-limited carriers

shift away from 5-axle tractor-semitrailers to these configurations to take

nem

Note that unlike the empty mileage analysis, estimating fuel
productivity changes from eliminating the 80,000 1b GVW cap is not concerned with
EQUIVWIT since the concern is on fuel productivity differences when carrying a
load.

3-28


1. INTRODUCTION

Heavy-duty trucks are an increasingly important source of carbon dioxide
emissions, since the rate of growth of fuel consumption has been substantially
higher than for other on-highway transportation sectors. Currently, heavy-
ducy trucks, defined by EPA as all trucks with a gross vehicle weight (GVW)
greater than 8500 lb, account for about 28 percent of total on-highway fuel
consumption. As a result, there is considerable interest regarding this
market segment's future fuel consumption. The EPA’s interest lies in
identifying areas where there is scope for the implementation of policies to
reduce fuel consumption without changing the level of service provided by the

trucking industry.

Unlike the light-duty segments of the fleet, there is no standardized measure
of fuel economy for heavy-duty trucks. The only reliable source of
information on truck fuel economy is the Truck Industry and Use Survey (TIUS).
This survey is conducted by census once every five years and the 1987 TIUS,
conducted in calendar year 1988, is the most recent publicly available
version. The TIUS was analyzed to establish historical values of fuel economy
and fuel economy improvement The TIUS also contains a wealth of other data
on truck annual use, scrappage, distribution by weight class and body style,
etc all of which are relevant to a fuel economy study. The analysis of TIUS

data and the results are documented in Section 2

Truck fuel economy is more accurately measured in terms of ton-miles of
payload carried per gallon, which is affected by operational and technological
factors. Operational factors that affect fuel productivity include average
payload weight, empty backhaul, and maximum allowable size and weight. All of
these issues have become important, since the competitiveness of the trucking
industry not only depends on truck technology but also on operational

factors. Two factors - empty backhaul and maximum allowable size/weight are


TABLE 4-1
SENSITIVITY OF FUEL ECONOMY

TO TRUCK LOAD

Class 6 Truck, 155 HP 7.3 L Navistar diesel.

Class 8A Truck, 210 HP DT 466 Navistar diesel.

Gross Weight

8,000
13,000
18,000
23,000
28,000

10,000
15,000
20,000
25,000
30,000
35,000
40,000

Gity F/E

Class 8B Truck, Cummins NTC engine.

Source:

30,000
40 ,000
50,000
60,000
70,000
80,000

Navistar Simulation City Speed:

9.48
8.72
817
7.63
7.15

AAI YH HOw
a
°

PRUUUD
°
a

Highway Speed:

18.6 MPH
53.0 MPH

SEI wo

Ars eE@


72-%

5.45

5.35

5.25

QOv=s

5.05

4.85

4.75

FIGURE 2-11

Average MPG By Vintage

GVW Class 8B Diesel Trucks

L n L

1

L

1977

1978

Model Year 1977 Includes 1977 and

pre-1977 models

1979

1980

1981 1982 1983
Model Year

1984

1985

1986

1987



and physically represents the percent change in fuel consumption due to a unit
change in the variable (e.g., a 10 percent change in the weight results in a
'X percent’ change in fuel consumption).

Volvo provided a general set of values for the energy demanded (and, hence,

fuel comsumed) over a typical European long haul cycle. These values are:

Inertia (Weight) 48.9 %
Aerodynamic Drag 17.4%
Rolling Resistance 24.6 %
Drivetrain Losses 590%
Accessories 3.8%

The above figures do not explicitly refer to idling and braking energy loss.
Moreover, Volvo stated that these figures are for a highly aerodynamic truck,
and that average values for aerodynamic losses on a U.S. highway cycle were
considerably higher. Other manufacturers suggested that, depending on the
cycle, aerodynamic drag could account for 30 to 50 percent of energy loss,
while imertia related losses were in the 30 to 40 percent range, at highway

speeds.

Volvo and Navistar provided data from computer simulations of the same
truck/emgine combination loaded to different weights Volvo provided data on
two trucks, a medium duty (Class 7) truck and a Fl2 longhaul truck rated at
100,000 1b GVW (50 tons). Class 7 trucks had a nominal fuel consumption of 30
1/100 km at 15 cons GVW and a sensitivity of 1.22 1/100 km per ton in city
driving. This leacs to a sensitivity coefficient of 0.55, i.e. a 10 percent
weight decrease results in a 5.5 percent fuel consumption decrease. The F12
truck had a nominal consumption of 50 1/100 xm at 55 tons GVW on a iong haul
driving cycle, and a sensitivity of 0.65 1/100 km per ton. This represents a
sensitivity coefficient of 0.715, which appears to be very high relative to
other opinions. However, this is consistent with the energy breakdown
provided by Volvo, as weight reduction reduces both inertial and rolling
resistamce energy loss, which Volvo determined as being 73.5 percent of total

energy:

4-3


9E-€

Truck Configuration

5-Axle
6-Axle
5-Axle
7-Axle
8-Axle
9-Axle

Rocky Mountain Doubles

Tractor-Semis.

Tractor-Semis.

Twin 28s
Twin 28s
Twin 28s

Twin 28s

Turnpike Doubles

1 Ton-Miles Per Gallon

NA - Not Applicable

TABLE 3-12

FUEL PRODUCTIVITY ESTIMATES FOR SIZE-LIMITED

VEHICLES AND POTENTIAL GAINS FROM SHIFTS TO LCVs

Fuel Productivity? Potential Gain From
With Uncapped Shifting to Rocky Mt
Bridge Formula Doubles

70.52 59 7%
70.24 60 4%
80 70 39.6%
79.84 41 1%
79.36 41.9%
78.87 42.8%
112.64 NA

137.38 NA

Potential Gain From
Shifting to Turnpike
Doubles

94.8%
95.6%
70.2%
72.1%
73.1%
74.2%
NA
NA


FIGURE 2-4
Average Operating Equivalent Weight

By GVW Class

Average EQUIVWT (x1000 tbs.)

|

ET

|
i

|

} |

\

|

60

40> 0-0 7

2-17

Class 7 Class 8A Class 8B

Class 6

GVW Class

Diesel

MMM Gasoline



On the other hand, 6-axle tractor-semitrailers and Twin 28s are limited by the
80,000 lbs GVW cap, since without the cap higher GVWs would be allowed by
Bridge Formula B. A typical 6-axle tractor-semitrailer with a 48 ft trailer,
a kingpin-to-rear-axle distance of 41 ft, a kingpin setting of 1 ft behind the
second axle (giving a distance between extreme non-steering axles of 42 ft),
and 12,000 lbs on the steering axle is allowed to ‘gross-out’ at 86,000 lbs
under Bridge Formula B. With 3 ft between trailers and assumptions similar to
those previously discussed for axle spacing, the Bridge Formula B GVW limits
for Twin 28s range from 91,500 lbs for 5-axle Twin 28s to 110,000 lbs for 9-
axle Twin 28s - with 7-axle and 8-axle Twin 28s ‘grossing-out’ at 99,500 lbs
and 104,500 lbs, respectively.‘ For these tractor-semitrailer and Twin 28
configurations axle-weight limits are typically satisfied so that maximum
practical GVWs are determined by the 80,000 lbs GVW cap. In practice,
however, 7-axle, 8-axle, and 9-axle Twin 28s seldom adhere to the 80,000 lbs
GVW cap and operate, under special permit, at higher weights that satisfy

Bridge Formula B and axle-weight limits.

LCVs also operate beyond 80,000 lbs under special permit Where not
restricted by a state’s length limits, LCVs comply with GVW limits that are
set by Bridge Formula B, axle-weight limits, and additional state specific
requirements concerning horsepower, braking, linkage, driver training, weather
restrictions, and route designation according to the type of LCV.*° Under
Bridge Formula B, a Rocky Mountain Double with 12,000 lbs on the steering
axle, a 48 ft lead trailer, a 28 ft rear trailer, and 3 ft between trailers,
is allowed to ‘gross-out’ at 108,500 lbs - assuming that the distance between
extreme non-steering axles is at least 74 ft. Turnpike Doubles that have two
48 ft trailers, with 94 ft between extreme non-steering axles and 12,000 lbs
on the steering axle, are allowed to operate at roughly 131,700 lbs under

Bridge Formula B.

The flexibility to choose vehicles and payloads that meet their needs
effectively and at the lowest cost is of great economic value to truck
companies and individual truckers that transport freight to and from markets.

For vehicle configurations that have 5 or more axles the maximum practical


advantage of higher fuel productivity. For example, the potential benefit to
a weight-limited carrier of shifting from a 5-axle tractor-semitrailer to a 6-
axle tractor-semitrailer is an increase in fuel productivity of about 7%.
Shifts to 5-axle Twin 28s can result in a fuel productivity gains of
approximately 13%, while shifts to 9-axle Twin 28s can result in a gain of
roughly 27%. In the short-run, however, Twin 28s may not be practical for
certain carriers because the ease of shifting to Twin configurations is
constrained by the following factors:®

* Previous investment in expensive equipment of long life,

particularly tanks, but also refrigerator units and concrete
mixers,

* The extra cost of handling Twins, which increases as a
proportion of total cost for short hauls,

¢ The extra cost of handling Twins in tightly constrained
terminal areas,

* Possible capacity constraints of shippers and receivers because
of limitations of space in existing facilities, particularly of
van operations that serve dense urban areas with high space
cost,

* Some shippers may be slow in changing production processes or
modifying their facilities to take advantage of potential
productivity improvements.

In the long run, the fuel productivity benefits of Twin 28s are expected to
outweigh the costs of operating these configurations for those carriers that
can benefit most from the added payload capacity. Terminal areas and existing
facilities will be redesigned to accommodate the handling of Twin 28s, current
equipment will depreciate and be replaced with Twin 28s, and shippers that
were previously slow in recognizing the productivity benefits of 7-axle, 8-

axle, and 9-axle Twin 28s will have reacted to potential gains

It should be noted that the analysis presented above describes maximum fuel
productivity attainable under each scenario. The analysis assumes that new
trucks operate at maximum payload capacity under both the capped and uncapped
Bridge Formula B scenarios and that trucks incur no empty mileage on a given

trip. Also, the estimated vehicle weight coefficient is lower in Model 7 than


0@-2

FIGURE 2-7
Average MPG By Vintage
GVW Class 8A Gasoline Trucks

6.50
6.00 ;---- Renee worn teres _
6.50 + ee ee eee ee a Jon nen en
M
P
°
4.50 |-- ee i
4.00 il 1 L L i i 1 L L 1 L
1977. 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987
Model Year

Model Year 1977 Includes 1977 and
pre-1977 modets


peak efficiency point. The net effect over the transient cycle is estimated
to be 1/2 to 1 percent benefit in bsfc. In urban driving conditions where the
engine spends much of its time at conditions where current turbochargers are

inefficient, the full 1.5 to 2 percent benefit may be realized.

Hence, the net benefit from improved thermodynamic efficiency is quite small
The most optimistic estimates place the benefit at about 3 percent while the

least optimistic at less than 1 percent.

Friction reduction in diesel engines is expected to occur by:
« improved component design,
« reduction of oil and cooling water flow, and
* reduction of governed RPM.

Current levels of friction in diesel engines relative to engines output is
already quite low. Mercedes provided data showing that a turbocharged diesel
engine rated at 285 HP had a total loss from friction, pumping and accessory
loads of 70 HP. Of this total, only about 30 HP was in friction loss. Hence,
the complete elimination of all friction, a practical impossibility, would
result in output increasing to 305 HP, and bsfc decreasing by 10 percent at
full load. However, the particular values cited are for a low BMEP engine
(135 psi). At a BMEP of 200 psi, complete elimination of friction will not
increase bsfc by even 7 percent at full load. However, at part load, the
friction loss (which stays nearly constant in absolute terms) becomes a much
larger percent of output, and friction reduction has a bigger effect on fuel
economy. An illustrative effect of friction of engine efficiency is shown in

Figure 4-3 for the Mercedes engine discussed above.

Actual friction reduction and internal loss reduction potential is quite
small. Mercedes has been experimenting with a special naturally aspirated
engine using a 2-ring piston, special fuel efficient oils, a low flow water

pump and a low flow oil pump, which reduced friction and accessory power loss


Finally, dummy variables were created to assess the impact of a vehicle's area
of operation and the presence of fuel economy engines or aerodynamic devices.
EEA used TIUS variables AREAOP, ECOENG, and AERODN to create dummy variables
DLOCAL, DECO, and DAERO.

Various linear and log-linear model specifications, employing different
combinations of the variables listed in Table 3-4, were tested to determine
the most statistically significant model for each GVW class and fuel type
combination. The following models were chosen based on their statistical and
analytical significance:

« For gasoline powered trucks, irrespective of GVW class, the model that
displayed the best statistical significance was;

1n(GPM) = atb*(MDLIDX)+c*ln(WIDWGT1)+d*1n(CIDCTR)+e* (DLOCAL)

* For diesel trucks with a GVW classification between 19,500 lbs and
60,000 lbs that model was;

1In(GPM) = atb*(MDLIDX)+c*ln(WIDWGT1)+d*1n(HPCTR) te*(DLOCGAL) +f* (DAERO)

¢ For diesel trucks in GVW Class 8B (60,000 lbs to 80,000 lbs) that model
was ;

In(GPM) = atb*(MDLIDX)+c*1n(WIDWGT1) +d*1n(HPCTR) +e*(DLOCAL) +£* (DAERO)+
g*(DECO)

The significance of the coefficient of aerodynamic devices on gasoline trucks
was not statistically different from zero, and thus the DAERO dummy variable
was excluded from that model The coefficients displayed no statistical
significance because of the small number of gasoline trucks that actually had
aerodynamic devices. For example, of the gasoline vehicles in Class 5 only

1 0% had aerodynamic devices Of all gasoline trucks in Class 6 only 1 4% had
aerodynamic devices, while of those in Class 7 only 0.9% had them (see Section
2). Similarly, other technology variables (such as the presence of radial
tires, variable fan drives and fuel efficient axle or drive ratios) were
tested but also did not display any statistical significance. Finally, note
that the engine control variable that displayed the best statistical
significance for gasoline powered trucks was engine displacement, rather than

horsepower. The lack of variability 1n horsepower across a GVW class/gasoline

3-17


4.6 IMPROVEMENTS TO THE ENGINE

As noted in Section 4.1, improvements to the diesel engine can be accomplished
by improving thermodynamic efficiency and turbocharger efficiency or by
decreasing friction and pumping loss. The net effect of these improvements is
to reduce the brake specific fuel consumption, or bsfc. While bsfe can be
measured at specific load/speed points, EEA has utilized bsfc as measured
over the EPA transient test cycle, which is designed to replicate engine
speeds amd loads over a city and highway driving schedule. As a matter of
interest, the engine manufacturers association (EMA) provided estimates of

bsfc by engine type to the year 2002. Table 4-4 reproduces the EMA

submission.

It is instructive to compare the actual bsfc attained in 1991 under the
prevalent 5.0 g/BHP-hr NO, standard with EMA’s projections for 1992 EEA
obtained detailed data from several select engine manufacturers and the data
is tabulated in Table 4-5. The bsfc of engines is a function of both the
horsepower rating and the rated RPM of the engines Increased horsepower
ratings result in lower bsfe as frictional and pumping losses become a smaller
fraction of total output. Lowering the rated RPM results in decreases in
friction loss. It can be seen from Table 4-5 that most manufacturer’s
products are similar, although some very modern designs such as Caterpillar's
311lb and 3176 models appear to have lower bsfc relative to older engines at
similar HP/RPM ratings It also appear that the EMA projections for 1992 are
very close to the actual values attained in 1991, with the medium-heavy-duty
engines currently at about 0 420 1b/BHP-hr compared to a predicted 0.413
value, and the heavy-heavy at about 0.365 1b/BHP-hr compared to a predicted
0.353. The light-duty engines are split between the older IDI design Navistar
with high bsfc relative to the more modern, turbocharged/aftercooled DI engine
from Cummins With the expected conversion of Navistar’s 7.3 L to DI, the EMA

bsfc projection of 0.466 1b/BHP-hr could easily be attained.

Given the relative accuracy of the EMA projection, it is interesting to

examine the projection to 2002. Between 1992 and 2002, no improvement is


SEe-€

Empty Weight (lbs)

Estimated Payload
Weight (lbs)

GVW Under Uncapped
Bridge Formula (lbs)

LHPCTR?
MDLIDX

% w/DLOCAL=1
% w/DAERO=1
% w/DECO=1

5-Axle
Semi.

26,800

24,500

51,300
-O 3376
11

14.7
100
25.4

PHYSICAL AND OPERATIONAL CHARACTERISTICS

OF SIZE-LIMITED 5-AXLE OR GREATER TRUCKS

52,800
-0.3088
11

14.7
100
254

TABLE 3-11

5-Axle
Twin 28

30,000

28, 600

58,600
-0.2045
1

14.7
100
25.4

7-Axle
Twin 28

34, 200

28,600

62,800
-0.1353
1L

14.7
100
25.4

8-Axle
Twin 28

9-Axle
Twin 28

Rocky Mt
Double

36,700

28,600

65,300
-0.0963
ll

14.7
100
25.4

39,200

28,600

67,800
-0.0587
1

14.7
100
25.4

LHPCTR estimates reflect AVWGHT of 35 95 tons for Class 8B trucks (Table 3-6).

36,000

41,700

77,700
-0.0776
11

14.7
100
25.4

Turnpike
Double

45,000

52,700

97,700
-0.3066
11

14.7
100
25.4


TABLE 4-4
ENGINE MANUFACTURERS ASSOCIATION
BRAKE SPECIFIC FUEL CONSUMPTION
HEAVY-DUTY DIESEL ENGINES
(AS MEASURED ON TRANSIENT TEST CYCLE)

Truck NO,
Class Standard 1977 1982 1987 1992 1997 2002
IIB 10 7 : -527 ~524 .451 .451 451
thru 7.0 - -527 2524 2453 -453 453
Iv 50 - +527 524 466 465 464
Vv 10.7 -467 457 -412 - 382 373 367
thru 7.0 482" 472° 418" - 386 377 370
VIIIA 5.0 516" 507" 454* -413 401 398
10.7 429 -400 343 321 310 308
VIII B 70 -438* .407* 348" 330 319 316
5.0 .491" 432" 2374" +353 340 +336

Based on less than total production.

Source’ EMA, 1983

4-19


benefit is expected to be greater than the loss in fuel economy. Fuel economy
losses will be relatively small because aerodynamic forces do not closely
scale with added vehicle weight and because heavier vehicles have larger
engines that can be more fuel efficient. On the other hand, changes in weight
limits affect not only the operating weights of today's trucks, but also the
types of equipment that motor carriers will operate in the future. If weight
limits are liberalized, some motor carriers will switch to vehicle
configurations that have higher empty weights. The difference in empty
weights between these new configurations and those used previously are small
relative to the difference in payload capacities. Seven-, eight- and nine-
axle double-trailer trucks with trailing units that are longer than 28 ft -
defined as Longer Combination Vehicles (LCVs) that are currently not allowed
to operate in most states - have empty weights between 30,000 and 40,000 lbs.
These vehicles operate at weights of well over 100,000 lbs, often carrying
payloads of over 70,000 lbs Conventional five-axle tractor semi-trailer
trucks, on which most freight is currently transported, are limited by law to
a maximum GVW of 80,000 lbs These vehicles usually have empty weights of
25,000 lbs and often carry payloads that weigh below 65,000 lbs Even if
changes in the weight limits induce a shift toward vehicles with higher empty
weights, the fuel productivity gain of the added payload capacity can be
significant Increasing payload capacity will also increase the cost
productivity of the vehicle's driver At a given driver cost more payload can

be carried.

Policies that liberalize weight limits are expected to increase fuel
productivity and operational productivity in the movement of freight by truck.
Weight limits are imposed at both the state and federal level However,
current federal regulations supersede many state limits, at least as they
apply to the interstate highway system on which a significant portion of fuel
is consumed.* Due to this, and because state regulations for non-interstate
roads vary from one state to the other, this report quantifies the effect on
fuel productivity of a change in the federal weight limit. Throughout the

analysis, size limits are assumed to remain unchanged.

3-4


2.3 CHARACTERISTICS OF HEAVY-DUTY TRUCKS

Class specific physical and operational characteristics are important in
determining the policy and technological options that best improve fuel
efficiency. The physical characteristics of a given truck include, among
other things, the truck's engine type (i.e., gasoline, diesel, LPG, or other),
engine size, and horsepower rating. Table 2-1 demonstrates the distribution
of trucks by engine type and GVW class. Over 50% of trucks in Class 6 and
Class 7 are propelled by gasoline, In contrast, only 20.5% of trucks in Class
8A have gasoline engines, while all trucks in Class 8B have diesel engines.
This suggests that diesel engine improvements, such as electronic fuel
injection timing control and improved intake and exhaust porting, will have
significant effects on the average fuel efficiency of Class 8A and Class 8B
trucks, but more modest effects on Class 6 or 7 trucks. However, sales data
in Table 2-2 shows that diesel penetration has increased markedly in these
classes. In 1980, 24.4% and 62.2% of new sales in Classes 6 and 7,
respectively, consisted of diesel powered trucks. By 1990, diesel sales
percentages had increased to 71.05% for Class 6 and 81.55% for Class 7, and a
shift away from Class 6 trucks to Class 7 and Class 8A trucks has taken place
Similarly, Class 8A is slowly being fully dieselized, while Class 8B has been
completely cieselized since the mid-1970’s, as it exclusively consists of

line-haul trucks.

Trends im engine size and horsepower ratings can help to explain changes in
average fuel efficiencies across GVW classes. Figure 2-1 shows average engine
size (CID) for gasoline trucks by GVW class and vintage. For virtually ail
classes, no significant changes have taken place in average CID. The small
dip in Class 8A trucks during model years 1982 to 1984 reflect the fact that
Navistar, the maker of the largest gasoline engines in the early 1980's,
exited that market. Similar data analysis for diesel trucks also showed no

significant engine size trends in any of the GVW classes.
Figure 2-2 shows average horsepower by GVW class and vintage for diesel

trucks There is a contention in industry that during the 1980s diesel engine

horsepower ratings had steadily increased, especially in the heavier truck

2-4


61-€

TABLE 3-5

LISTING OF FITTED MODELS

Model 1. GVW Class 6 (Gasoline Trucks)

LGPM = -1 7801 - © 00494MDLIDX + 0.2346*LWIWGTL
(0.0165) (0.0019) (0.0247)

Model 2- GVW Class 6 (Diesel Trucks)

LGPM = -1 7854 - 0.0278*MDLIDX + 0 2209*LWTWGT1
(0 0181) (0 0017) (0.0343)

Model 3- GVW Class 7 (Gasoline Trucks)
LGPM = -1 6990 - 0 0092*MDLIDX + 0.1963*LWTWGTL

(0 0235) (0 0025) (0 0316)

Model _4- GVW Class 7 (Diesel Trucks
LGPM = -1 7435 - 0 0300*MDLIDX + 0.2336*LWTWGTL

(0.0172) (0 0017) (0 0314)
Model 5: GVW Cl G. ine_ Truck:
LGPM = -1.5181 - 0.0102*MDLIDX + 0.1492*LWTWGTL

(0.3344) (0 0040) (0 0387)

Model 6: GVW Class 8A (Diesel Trucks)
LGPM = -1.6020 - O 0112*MDLIDX + 0.1743*LWTWGTL

(0.0085) (0.0009) (0 0123)

Model 7: GVW Class 8B (Diesel Trucks)
LGPM = -1.5546 - @ 0112*MDLIDX + 0.0426*LWTWGT1

(0.0032) (0 004) (0 0058)

+ © 4403*LCIDCTR + 0.0503*DLOCAL
(0 0391) (0 0133)

+ 0.0966*LHPCTR + 0.0337*DLOCGAL - 0.0691*DAERO
(0.0512) (0 0123) (0.0227)

+ 0.5560*LCIDCTR + 0.0180*DLOCAL
(0 0602) (0.0193)

+ 0.0930*LHPCTR + 0.0635*DLOCAL - 0.0415*DAERO
(0.0522) (0.0125) (0.0228)

+ 0.5729*LCLDCTR + 0 0416*DLOCAL
(0 0985) (0.0223)

+ 0,0630*LHPCTR + 0.0509*DLOGAL - 0.0573*DAERO
(0 0099) (0.0061) (0.0096)

+ O.1113*LHPCTR + 0.0255*DLOCAL - 0.0181*DAERO - 0.0275*DECO

(0 0072) (0.0029) (0.0043)

Standard errors of the coefficients are shown in parenthesis.

For definitions of the variables see Table 3-4

(0047)


the appropriate GVW category. Reported values for make, fuel type, fuel
economy, engine size, horsepower, number of cylinders, and maximum loaded
weight were compared to expected values (or ranges) for the truck’s
appropriate GVW category. An ‘’exception’ score was kept for each truck.
Every out -of-the-expected-range value added 1.0 to this score. If a truck did
not report a value for some parameter, the score was incremented by 0.5.
Third, trucks with ‘exception’ scores of 2.0 or greater were eliminated from
the data set. A total of 6,661 trucks were eliminated on this basis. Trucks
with ‘exception’ scores of 1.5 or less were accepted in the cleaned data set
There were 18,545 trucks (out of 97,945) in the cleaned data base that had
‘exception’ scores of 1.5 or less. The majority of these trucks simply

exhibited missing values for engine size, horsepower, or weight.

This clean-up procedure resulted with the following truck distribution by GVW

class
GLASS gv Sample Size
1 6,000 or less 31,367
2 6,001 to 10,000 10,895
3 10,000 to 14,000 3,334
4 14,001 to 16,000 1,768
5 16,001 to 19,500 1,934
6 19,501 to 26,000 8,927
7 26,001 to 33,000 5,251
8A 33,001 to 60,000 12,415
8B 60,001 to 80,000 20,521

The small samples for Classes 4 and 5 verify low sales volumes in this market.
Although this market is technically recognized by industry to be part of the
heavy-duty truck market, the fact that only 5% of all heavy-duty trucks are
light-heavy-duty trucks allows for analytical emphasis on the heavier
populations. Therefore, EEA disregards Classes 4 and 5 from the analysis, as
well as light-duty vehicles (i.e , Classes 1, 2, and 3). Finally, 1,533
trucks were found to typically operate beyond 80,000 lbs. These trucks do not
posses consistent physical and operational characteristics, so they were also

disregarded from most of the analysis.

2-3


Finally, those trucks whose greatest percentage of mileage was accrued off-
road were also deleted from the "active" data base. Such vehicles do not
operate on the interstate highway system and have physical and operational
characteristics that are not consistent with commercial trucks. EEA also
investigated the statistical differences between trucks that are predominantly
used for agricultural services, rough use services (i e., construction,
forestry and mining), and regular commercial services (such as, wholesale
trade, retail trade, manufacturing, refining, or processing activities, etc).
The statistical differences were not significant and a distinction in the

analytical procedure was deemed inappropriate.

Fuel productivity is usually defined as ton-miles per gallon, or the number of
freight ton-miles traveled per unit of fuel that is consumed. Therefore, to
determine the effect of lifting the 80,000 lbs GVW cap and the effect of empty
mileage on fuel productivity, it was necessary to devise models that explain
the functional relationship between the rate of fuel consumption (as defined
by GPM, or gallons of fuel consumed per miles traveled) and the variables that
influence this rate These variables should theoretically represent actual
operational and physical characteristics of a given vehicle, or vehicle class,
so that when changes in these variables take place the rate of fuel

consumption for that vehicle will adjust accordingly

Table 3-3 defines relevant TIUS variables used in the analysis. From these
variables fuel productivity can be defined as (AVWGHT - EMWGHT) * MPG. The
difference between AVWGHT and EMWGHT is the typical payload weight of a
vehicle - since AVWCHT is defined as EMWGHT plus weight of cargo This
difference multiplied by MPG equals, by definition, payload-miles (or ton-
miles) traveled per gallon of fuel consumed. However, such an estimate of
fuel productivity does not take into account the effect of empty mileage on
fuel productivity or the effects of a vehicle's physical and operational
characteristics on MPG [such as, the vehicle's engine size (CID) and
horsepower (HRSPWR), the vehicle's age (MODELYR) and area of operation
(AREAOP), or the presence of aerodynamic devices (AERODN) or a fuel economy
engine (ECOENG) ]


PNOLOD rates are so high implies that carriers can benefit greatly by reducing

empty mileage.

Having characterized the average annual mileage that trucks operate without a
load, average operating weight can be estimated using TIUS variables EMWGHT
and AVWGHT. The EMWGHT variable describes a given truck’s empty weight, while
AVWGTH describes the empty weight plus weight of cargo of a truck when
carrying a typical payload. Therefore, the average operating weight of a
truck can be defined by the following weighted sum:

[AVWGHT*(1-PNOLOD) + EMWGHT*(PNLOD) ].
EEA defines this estimate of average operating weight as equivalent weight
(EQUIVWI). The equivalent weight of a vehicle will have a considerable impact
on the vehicle’s average fuel consumption rate (MPG). Figure 2-4 shows

average EQUIVWT by GVW class/engine type combination.

Model year trends in gasoline fuel economies (MPGs) are plotted by class in
Figures 2-5 through 2-7 for Classes 6, 7 and 8A The error bars give the high
and low ends of the standard deviations of the means An increasing trend in
fuel economy is apparent since 1984 for both Class 6 and Class 7 gasoline
trucks, while Class 8A gasoline trucks show no trend in MPG. Diesel fuel
economy trends are plotted in Figures 2-8 through 2-11. In each GVW class,

diesel MPGs have consistently increased since model year 1977.

2-16


applications and the percent of trucks that allow the use of drag reduction
devices. The estimate is available by GVW class and fuel type - gasoline in
Table 2-4 and diesel in Table 2-5. EEA has defined ‘rough’ operation as those
trucks used in construction, forestry, and mining. ‘Regular’ use trucks, such
as trucks used in wholesale or retail trade, mostly include enclosed vans and

tank trucks.

Area of operation also has a direct impact on a truck's fuel efficiency.
Long-haul trucks that mostly operate on interstate highways at constant speeds
are expected to be more fuel efficient than short-haul trucks that operate at
city cycles, all other things being equal. Table 2-6 characterizes each GVW
class/fuel type combination by the percent of trucks that can be characterized
as local, short-haul, and long-haul. As expected, the percent of Class 8B
trucks operating locally is substantially less than in any other GVW class.
Class 8B includes mostly line-haul vehicles that operate on interstate and

intra-state highways at near constant speeds.

The single most important operational factor influencing a truck’s fuel
efficiency is it's average operating weight on a given trip. At any given
moment im time, the operating weight of a truck is defined as the empty weight
of the truck plus the weight of cargo being hauled. However, on any given
trip a typical truck will encounter some empty mileage (i e, when no cargo is
being hauled) and some loaded mileage (i.e., when cargo is being cransported).
To estimate the average operating weight of a truck it is necessary to account
for both empty and loaded mileage TIUS variable PNOLOD describes the
approximate percentage of a truck's annual mileage during which no payload was
carried, Figure 2-3 shows average PNOLOD by GVW claess/fuel type combination.
Average PNOLOD is surprisingly high in all GVW classes, with gasoline trucks
showing higher rates than diesel trucks. One would expect empty mileage to be
substantially lower in Class 8B, since it largely consists of line-haul
trucks. Line-haul trucks, and other commercial trucks, attempt to minimize
empty mileage because fuel productivity (i.e., ton-miles per gallon of fuel

consumed) is equal to zero when empty operation takes place The fact that

2-11


analyzed in Section 3. This analysis relies on TIUS data as well as on
information obtained from the American Trucking Association and other

organizations about the operational characteristics of heavy-duty trucks.

Truck technology is also a major force in improving truck fuel productivity.
The advent of stringent new emission standards has created the argument that
future technological benefits to increase fuel efficiency may counterbalance
the negative effects of emission standards and, thus, that an increase in fuel
productivity may not take place. A detailed analysis of all of the
technological improvements likely to occur over the next decade is provided in
Section 4, Data for this Section were developed from interviews with major
U.S, and European manufacturers of trucks and truck engines (European
manufacturers have recently acquired major U.S. truck manufacturers). Even in
the absence of any regulatory incentives, EEA'’s analysis shows that truck fuel

economy will continue to improve, at least at the historical rate

1-2


€-V

CORRB

NTERCEP
HOL1Dx
LWTWGTL
LcrpcTR
DLOCAL

EEA GW Group=26 000-33,000 Lbs

Source

Model
Error
C Total

Root HSE
Dop Hoan
cy

Varteble DF

INTERCEP 1
*WLIDX a
LHTWGT? 1
terocikR =
DLOCAL 1

INTERCEP

1 0000
0 4401
0 5651
-0 0227
-0 7205

MODEL 3

Dependent Variable: LCPM

Type of {uel used by vehicle~Gesoline

Anelyats of Verience
Mean
oF Squere
‘ 12 78172 319543
2015-181 68901 0 09017
2019-198 47073
9 30028 = -R-square
1 78895 Ad
-16 70527

Parameter Estimates

Parameter
Esticate

-1 698965
-0 009167
0 196288
© 555998
a 18047

Standerd Tt

F Velue Prob>F
35 439 0 0001
© 0657
0 0639
or AD

Error Parameter=0

0 02354247
© 00253633
© 03159836
© 06024026
© 01933636

Correlation of Estimate:

MDLIOX

-0 4402
2 0000
-O 1326
-0 1493
0 1339

LWTWGT1

0 S451
-0 1326
1 0900
-0 1237
0 0369

“72 166
-2 618
6 212
9 228
9 933

Prob > |r|

oaoo
0003
9001
ooo1
3508

eoeee

LCIpcTR

-0 0227
-0 1493
-0 1237
1 9000
0 0202

DLOCAL

-0 7205
0 1339
0 0369
0 0202
1 0000



Ex, is the energy required to overcome aerodynamic drag,

Ex is the energy lost to inertia forces during acceleration or
climbing gradients,

Bac is the energy used by accessories,
is idle fuel consumption,
ty is time at idle,

ty is time of braking.

For large diesel trucks, E,, is generally small relative to E,, Ex, and Ep
Depending on the cycle, the value of G(t, + t,), which represents fuel used
during periods of no useful engine output, can be quite small since G, idle

fuel consumption per unit time, is low for a diesel engine.

The above equation points to methods to improve fuel consumption Improve-
ments to bsfc can be accomplished by:

¢ increasing engine thermodynamic efficiency,

* reducing friction loss,

* reducing pumping loss, and

« increasing turbocharger efficiency
Fuel consumption can also be reduced by reducing the vehicle related parame-
ters of weight, drag and rolling resistance or reducing accessory loads. Idle
fuel consumption can be reduced by reducing idle time, i.e. switching off at
idle, and by reducing the engine displacement. In the case of weight reduc-
tion, we are referring to the empty weight of the truck. Reduction in empty
weight will reduce truck total weight, allowing either an absolute weight

reduction or an increased payload capacity (when trucks are limited by the

weight rather than the size of the payload).

4.2 FUEL PTION SENSITIVITY

The sensitivity of fuel consumption over any specific driving cycle to a
particular independent truck attribute, such as weight, can be represented as

the derivative of the equation relating fuel consumption to these variables,

4-2


12-%

FIGURE 2-8
Average MPG By Vintage
GVW Class 6 Diesel Trucks

8.50

8.00

7.50

7.00

Qvs

6.50

6.00 > J - > — ee cents tee ee ee ee
5.50 Ld. i 1 1, 1 4 im 1 L 1 1
1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987

Model Year

Model Year 1977 Includes 1977 and
pre-1977 models.


FIGURE 2-1
Average CiD By Vintage and GVW Class

Gasoline Trucks

cID

Al)

Ks

AIIM

WW

AU

MM

ANIM

MMM ID

KX

ANN)

MIM]

WM)

AW

ANON IM

IW

500

400 ;-
3007]
200

2-7

1983 1984 1985 1986 1987

1982
Model Year

Class6 EAciass7 [_lclass an |

ct

Modet Year 1977 Includes 1977 and

Pre-1977 models


TWIN TRAILER OR “OOUBLES”

, 28° 11 23° I

Source:

Figure 3-1

STRAIGHT TRUCK S-AXLE TRACTOR SEMITRAILER
|— 2: ]——24' - 29 —|
4-AXLE TRACTOR SEMITRAILER S-AXLE TRACTOR SEMITRAILER
3a! - 48° | - 48!
S-AXLE TRACTOR FLATBED TRAILER S-AXLE TRACTOR TANK TRAILER
3a!’ 42° ! a5’ + 40 {

é<—~  @==—y

ROCKY MOUNTAIN DOUBLES
(onacated only in certain states)

45! - sa"

TURNPIKE DOUBLES
(operated onty in certain states)

- 48°

LENGTHS SHOWN ARE TYPICAL; SHORTER OR LONGER LENGTHS
ARE POSSIBLE DEPENOING CN CARRIERS NEEDS AND STATE LAWS.

ATA, American Trucking Trends, 1989 3-2


* potential increase in brake specific particulate emissions due
to lowered intake airflow,

* and no significant reduction in heat transfer.

While Cummins was in general agreement with Mercedes and saw no benefit to
ceramic "hot internal parts" at a 4.0 g/BHP-hr standard, Caterpillar was
notably more optimistic. Gaterpillar suggested that a ceramic cylinder head
was a distinct possibility even without turbocompounding, and that with
turbocompounding, ceramics could increase the total bsfc benefit from 5 to 7

or 8 percent at rated speed.

All manufacturers stated that some turbocompound engines would be introduced
in 1994/1995 but this technology would not have high market penetration by
2001.

4.8 DRIVETRAIN OPTIMIZATION

The drivetrain parameters are selected for a given truck gross weight and
engine combination to meet a variety of performance requirements, such as fuel
economy, ‘on-grade’ startability, capability to negotiate a grade at a
selected speed and vehicle top speed requirements. Once a customer has
selected an engine with a specific peak torque and RPM rating, the transmis-
sion and drive axles must be selected to optimize among the various require-
ments ., The selection is based on the power/torque rating of their compo-
nents, the ratio coverage of the transmission, the number of gears, and the
axle ratio. Historically, the choice was sometimes constrained by availabili-
ty of transmissions, and parameters were selected to optimize overall "perfor-

mance", even at some slight loss of fuel efficiency,

In Glass 8B trucks, inefficient drivetrain parameters were chosen by fleet
operators to limit driver top speed rather than match for best efficiency. At
highway cruising speed on level roads (e.g., 55 to 60 mph), it is most fuel
efficient to operate the engine closer to peak torque RPM, which is typically
60 percent of rated RPM. However, selection of gear and axle ratios to

achieve this RPM results in a truck with a capability to exceed 70 mph at


"0-4

16

12

Figure 4-3
Effect of Reducing Friction on
Engine Efficiency

Increase in Efficiency

2100 RPM
10 APM

800 RPM


FIGURE 2-2
Average Horsepower By Vintage and

GVW Class (Diesel Trucks)

Horsepower

VK

AMY

ANIM

WW

400

300

200 |-

1978 1979 1980 1981 1982 1983 1984 1985 1986 1987
Model Year

1977

Class 8B

U_ictass 8a

BCA Class 7

Ml class 6

|
|
|
|

2
e
©
6
x
°
°
©
2
2
ry
&
6
~
o
s
g
s
.
°
=

a
2
2
9
€
K
@
e
a

|



At meetings with manufacturers held in conjunction with this analysis, most
engineers contested the large values of fuel economy benefit initially
reported by Cummins. Mercedes stated that their tests had shown a 2 percent
benefit in fuel efficiency with heat insulation of the exhaust manifolds and
ports. Caterpillar was more optimistic, and cited recent development showing
a 4.7 percent lower specific fuel consumption at rated speed and a 3.3 percent
benefit at peak torque RPM. Cummins engineers also stated that a 4 percent
benefit for turbocompounding may be representative over a typical driving

cycle.

Turbocompounding has other benefits. Since the turbine obtains power from
waste heat, the engine emissions per unit of useful work are decreased
Typically, che turbine output is in the range of 10 to 12 percent of recipro-
cator output. If absolute engine-out emissions stay constant with and without
turbocompounding, a proportional 10 to 12 percent reduction in brake specific
emissions is implied. Indeed, Caterpillar found that at 4 O g/BHP-hr NO,, the
turbocompound engine had 8.0 percent lower bsfc at rated RPM and 3 5 percent

lower bsfc at peak torque RPM.

It has also been suggested that heat insulation of the cylinder would be
particularly useful with turbocompounding. Proponents of ceramic components
have discussed the heat insulation of the cylinder head, piston top, and
cylinder liners as a means to recover the heat wasted to the coolant
Performance assessments of ceramic components for low heat rejection engines
completed in the 1985-1988 time frame suggested additional fuel efficiency
benefits of 3 to 4 percent at full load, and ‘up to 13 percent’ at part load
for high swivel engines. Tests conducted by heavy-duty diesel engine manufac-
turer have failed to produce such benefits. In fact, most of the manufactur-
ers interviews had very negative perceptions of ceramics for use as heat
insulation for the cylinder. Mercedes stated that the very high temperatures

of the ceramics had the following negative effects:
* decreased volumetric efficiency,

* increased NO, emissions,

4-30


These benefits are percentage increases in MPG for the fleet as a whole due to

adoption of electronic control.

4.10 OTHER IMPROVEMENTS

Small improvements in engine and drivetrain related components will occur due
to evolutionary changes in design, leading to small improvements in fuel
economy. The use of synthetic lubricants in the engine, gearbox and axle lead

to small decreases in drivetrain friction, that also can benefit fuel economy.

The largest power drain from accessories comes form the cooling fan. Thermo-
statically activated cooling fans operate only when required by the engine and
can improve fuel economy significantly; however, most new trucks already
incorporated this device by 1978. Modest improvements can be made to the air
compressor, water pump and power steering hydraulic pump For example, Eaton
has recently unveiled a variable assist power steering system that cuts the
pump’s power absorption by up to 50 percent. Currently all of the accessory
loads take up 7 to 10 percent of total engine power output, and a slightly
larger share of fuel consumption While gains from improvements to existing
accessories will improve fuel economy in the range of 0.5 to 1.0 percent,
there is a tendency to increase the level of accessories to improve driver
comfort and safety These considerations can lead to an increase in accessory
loads from demands for air suspension, antilock brakes and other interior
power equipment. As a result, net accessory power decrease is unlikely to

decrease and could actually increase over the next decade

Synthetic lubricants have been available for over 10 years but have not
achieved significant market penetration. Lubricant manufacturer sponsored
testings showed significant benefits in fuel economy from their use - up to 4
percent - but truck industry experts suggest that 1 to 2 percent benefits are
more appropriate Improvements to conventional lubricants have also occurred
through the use of friction modifications and viscosity under improvements.
Such improved non-synthetic oils are more likely to find widespread acceptance

due to their lower price. A fuel economy gain if 1 percent in city driving

4-35


fuel productivity for Rocky Mountain and Turnpike Doubles can be derived.
Under a weight-limited scenario, the fuel productivity of Rocky Mountain
Doubles is estimated at 165.30 ton-miles per gallon and that of Turnpike
Doubles is estimated at 189.8 ton-miles per gallon. Under a size-limited
scenario, fuel productivity is estimated at 102.21 and 123.07 ton-miles per

*** In either case, LCV fuel productivity is much

gallon, respectively ”
lower when estimates are derived using Model 8. However, since it is not

inconclusive that Class 9 (regular use) represents only LCVs, the estimates
derived from Model 8 should be regarded as conservatively low, since other

configurations with inefficient engines may be included.

3.6 SUMMARY OF RESULTS

This section of the report has investigated two factors that greatly influence
fuel productivity, as defined by ton-miles per gallon of fuel consumed. These
factors are. 1) the prevalence of empty mileage, or mileage incurred when a
truck is not carrying payload, and 2) the effect of lifting the 80,000 lbs GW
cap that is imposed by the Federal government on trucks travelling the
interstate highway system and other federally-aided roads Empty mileage
affects all commercial trucks, while the 80,000 lbs GVW weight limit
constrains the payload capacity of heavier trucks, usually 5-axle or greater

configurations.

Empty mileage has a severe detrimental impact on fuel productivity, since when
a truck operates empty fuel productivity is equal to zero EEA determined
that avoiding empty mileage can potentially increase fuel productivity by 35
to over 60 percent, depending on GVW class and engine type combination.
However, there are many reasons why these potential increases will not be
realized; such as, the lack of perfect information regarding available hauls,

time restrictions, and backhaul restrictions at the state level

tae

Estimates for Rock Mountain Doubles using model 8 are based on a LHPCTR
of 0 1371 (weight-limited) and -0.1968 (size-limited) For Turnpike Doubles they
are based on a LHPCTR of 0.3309 (weight-limited) and 0 0322 (size-limited)
AVWGHT for class 9 regular use trucks is 47.3 tons.

3-38


Navistar provided data on fuel economy for a Class 6, a Class 8A, and a Class
8B truck over two driving cycles, at different loaded weights. The Navistar
data is shown in Table 4-1. Using these data EEA calculated the sensitivity

coefficients for different truck classes as follows:

GVW Class Gity Highway
6 0.307 0,146
7/88 0.369 0.188
8B 0.523 0.298

These coefficients are much lower than those shown by Volvo, and are more
consistent with the results from regression analysis of TIUS data. For
example, TIUS data shows a weight sensitivity of roughly 22 percent for Class
6/7 trucks, which is between the city and highway coefficients shown above.
However, the TIUS data shows a much lower sensitivity for Class 8B trucks that
are at odds with predicted trends shown above, as well as with the absolute
magnitude. Actual testing conducted on Class 8B trucks by Freightliner
Corporation showed that a 80,000 lb truck with a fuel consumption of 4 MPG
(0.25 GPM) had a fuel consumption decrease of 0.0029 GPM per ton weight
increase, for a sensitivity of 0.46, intermediate to the city/highway values

predicted by Navistar's simulation.

Aerodynamic drag reduction sensitivity factors have not yet relied on accurate
measurements of C, reduction versus fuel economy on a fixed test cycle The
only comprehensive data on Cy reductions and fuel savings is based on study of
a roof fairing for a 80,000 1b tractor trailer, conducted by GMC ?/ The
measured drag coefficient for the base (no aerodynamic device) tractor trailer
was a Cy of 0.770. Typical reductions of Cy were measured at different yaw

angles with the aerodynamic device and a mean (wind averaged) value of ACp was

4-4


Class 6
Non-Aero
Aero
Total”
Class 7
Non-Aero
Aero
Total”
Class 84
Non-Aero
Aero
Total”
Class 8B
Non-Aero
Aero

Total*

TABLE 2-5

DIESEL TRUCKS BY USE AND BODY STYLE
PERCENT BY GVW CLASS

Agricultural Rough Use Regular Use Total”
76.6 88.8 43.4 53 6
234 11.2 56.6 46.4
10 4 14.7 74.9 100 0
715 93.8 46.0 56.6
28.5 62 54.0 43.4
10 2 16 6 73.2 100.0
79 8 94.8 44.8 62.7
20.2 5.2 55.2 37.3
10.4 28.4 61.2 100.0
72 2 92.7 37.7 51 2
27.8 7.3 62 3 48 8
93 18.6 721 100.0

* Horizontal Total reflects % of trucks in a class by type of operation.

“Vertical Total reflects % of trucks in a class by body style

2-13


rated RPM. Many fleet operators specify a numerically high axle ratio to
prevent overspeeding. A more fuel efficient axle ratio selection with
additional road speed control can provide 3 to 5 percent improvement at the
same reference speed. This improvement is possible for the portion of the
feel where, currently, axle ratios are misspecified. Anecdotal information
suggests that about 30 to 50 percent of Class 8B trucks may have unoptimized

drive-trains.

In medium-duty trucks, greater scope exists for drivetrain optimization, since
the choices of gear ratios, gearbox torque capability and axles were supply
limited. For example, virtually no transmissions were available with a rating
between 650 ft-lbs of torque and 1000 ft-lbs. This situation has been
changing with the introduction of transmissions from Spicer and Fuller with
ratings of 750 ft-lb and 975 ft-lbs, for example. As a result, the medium
duty truck customer can choose the low RPM, high torque engine models without
paying a very large cost penalty for transmissions and driveshafts with
ratings substantially higher than required. However, the fuel economy benefit
associated with using lower governed speed engines is accounted for in

Section 4.7

Other improvements to the transmission include the incorporation of single-
plate rather than double plate clutches. New cerametallic materials allow
single plate clutches to effectively replace double plate clutches, resulting
in a small (0 5 percent) increase in city cycle fuel economy More recently,
Eaton has introduced a new automated 9-speed transmission called ‘'Econoshift’
that automates the shifting in the top two gears so that the correct gear will
be chosen automatically at speeds above 45 mph. Eaton stated that the
Econoshift would cost $1500 more than a traditional transmission but pay for
itself im 18 months, suggesting a fuel economy improvement as large as 5
percent in Class 8B trucks. It is not clear how Eaton arrived at this

benefit, as the benefit would depend on the reference baseline.

Increased levels of market penetration are forecasted for automatic transmis-

sions in the lightest medium-duty trucks and bus markets. Although the


8T-2

7.00

FIGURE 2-5
Average MPG By Vintage
GVW Class 6 Gasoline Trucks

6.50 |-

6.00} f.. :

6.50  - —-f-

QvsS

6.00 ~~~

4.00 : 1

L 1 L L 1 H

1977 1978

Model Year 1977 Includes 1977 and
pre-1977 models

1979 1980 1981 1982 1983 1984
Model Year

1985 1986

1987



€t-€

TABLE 3-7
THE EFFECT OF EMPTY MILEAGE

ON FUEL PRODUCTIVITY

Fuel Productivity?

Fuel Productivity! With Without Empty Mileage Potential Gain From
GVW Class Empty Mileage (WIDWGT1 (WTDWGT2) Eliminating Empty Mileage
Class 6 Gasoline 22.95 33 67 51 33%
Class 6 Diesel 23.77 32.56 36.98%
Class 7 Gasoline 28.82 44.17 53.26%
Class 7 Diesel 33.65 45.04 33.80%
Class 8A Gasoline 38.06 61.51 61.61%
Class 8A Diesel 44.37 64.63 45.66%
Class 8B Diesel 77 53 112.29 44.31%

1 Ton-miles per gallon


1991 reduced fuel economy by about 2.0 percent, approximately counterbalancing
the gain achieved through the introduction of air-to-air intercoolers. Hence,
net gain of 5.5 percent is forecast at the 5.0 g/BHP-hr NO, standard between
1987 and 2001. However, the 1998 NO, standard of 4.0 g/BHP-hr could impose
significant bsfc reduction, and it is possible that the loss could be as large
as 5.0 percent, negating all of the technology benefits. This forecast
closely corresponds to the opinions of most manufacturers of heavy-duty
diesels, Starting from a 1987 bsfc of 0.365, the bsfc at a 5 0 NO, standard
will be 0.346 1b/BHP-hr in 2001.

Larger improvements will be available for the medium and light diesels. In
1987, most medium duty diesels were not intercooled, but the new emissions
standards for 1991/94 have forced a large majority of these engines to adopt
air-to-air intercooling. In addition, the adoption of lower governed speeds
will result in more engines moving to the 2300-2400 RPM ratings from the
current 2500-2600 RPM ratings, with some engines moving to 2100 RPM A net
bsfc reduction of 9.0 percent relative to 1987, at a 5.0 NO, standard is
forecast. This implies that bsfe will decline from 0.425 1b/BHP-hr in 1987 to
0.390 1b/BHP-hr in 2001.

The largest gains in fuel efficiency will occur for the light-heavy engines
that are used only in a few Class 5/6 trucks and school buses. This largely
stems from the conversion of the IDI diesels in this segment to Direct
Injection (DI) Currently, these engines are mostly indirectly injected V-8
designs rated at 2800 to 3000 RPM. By 2001, it is anticipated that they will
be replaced by turbocharged and aftercooled, direct injection diesels, with a
32.5 percent decrease in bsfc for the segment as a whole Starting from an
average bsfc of 0.540 1b/BHP-hr, the average bsfc will decline to 0.408
1lb/BHP-hr. This forecast is the only one that differs significantly from
the 1983 EMA forecast; yet, the presence of the new Cummins BT5.9 engine
with a bsfc of 0 400 lb/BHP-hr in this class suggests that the forecast is

conservative.

4-28


Surface Transportation Assistance Act of 1982 (STAA of 1982) was passed into
law. This act resolved the uniform weight issue and expanded the role of
federal regulations to other federally-aided primary roads. Regulations
brought about by the STAA of 1982 are valid today.

Under the STAA of 1982, Congress requires all states to allow on the
interstate highway system and primary roads receiving federal-aid the
following weights: a maximum load of 20,000 lbs on single-axles, a maximum
load of 34,000 lbs on tandem-axles (a tandem-axle is a pair of closely spaced
axles), and an overall gross weight on a group of two or more consecutive
axles produced by application of the Federal Bridge Formula B, provided that
such overall gross weight does not exceed 80,000 lbs. Bridge Formula B is

specified as follows:

W = 500 {LN/(N - 1) + 12N + 36]

where, W = maximum weight in pounds carried on any group of two or more
axles,

L-= the distance in feet becween the extremes of any two or more
consecutive axles,

N = the number of axles on the vehicle.

The intent of Bridge Formula B is to limit axle weights so that trucks do not
over-stress bridges on interstates and the federal-aid highway network. Under
the Bridge Formula, gross weights are allowed to increase as the number of
axles and the length between axle groups increase. However, the overall gross
weight of a vehicle cannot exceed 80,000 lbs, except for those vehicles
carrying loads which cannot be easily divided and which have been issued

special permits in accordance with applicable state laws.

State laws also determine the length of the trailing units of tractor trailer
combinations. The STAA of 1982 prohibited states from limiting the length of
the semitrailer of a tractor-trailer combination to less than 48 ft or each

trailer of a combination with two trailers to less than 28 ft on the

3-6


TABLE 2-6

PERCENT OF TRUCKS BY AREA OF OPERATION
BY GVW CLASS AND FUEL TYPE

GVW _Class/Engine Type % Local
Class 6 Gasoline 84.4
Class 6 Diesel 66.1
Class 7 Gasoline 86.2
Class 7 Diesel 66.4
Class 8A Gasoline 86.3
Class 8A Diesel 63.4
Class 8B Diesel 25.4

Area of Operation!

% Short -Haul %_Long-Haul
13.8 1.8
27.8 6.1
12.5 1.3
29.0 4.7
119 1.8
244 1221
32 9 41.7

Local if greatest percentage of annual miles were accrued within a 50

mile radius of home-base.
accrued between 50 to 200 mile radius of home-base.

Short-haul if greatest percentage of miles were

Long-haul if greatest

percent of miles were accrued beyond a 200 mile radius of home-base.


The typical payload for cube-limited 5-, 6-axle tractor-semitrailers and Twin
28s are estimated at 24,500 lbs and 28,600 lbs, respectively.” At an average
payload of 28,600 lbs, cube-limited Twin 28s operate with a typical freight
density of 4.45 pounds per cubic ft. Recognizing that Rocky Mountain and
Turnpike Doubles have volumetric capacities that are 2,941 and 5,406 cubic ft
greater than Twin 28s, average payload for these LCVs can be approximated if
the freight density for cube-limited Twin 28s is held constant. At a freight
density of 4.45 pounds per cubic ft, a Rocky Mountain Double can carry
payloads that are approximately 13,100 lbs greater than the typical Twin 28,
while a Turnpike Double can approximately carry an additional 24,100 lbs when
compared to cube-limited Twin 28s. Therefore, Rocky Mountain Doubles are
expected to operate with an average payload of 41,700 lbs, while Turnpike
Doubles are expected to operate with an average payload of 52,700 lbs.

Having determined the average payload weight of size-limited 5-, 6-axle
tractor-semitrailers, Twin 28s, Rocky Mountain, and Turnpike Doubles, fuel
productivity estimates can be derived for size-limited vehicles using Model 7
and the typical physical and operational characteristics presented in Table 3-
11. Data for size-limited trucks in GVW Class 8B was used to determine the
values for DLOCAL and DECO. LHPCTR was scaled in accordance with increasing
GVWs across axle configurations. The values for MDLIDX and DAERO implicitly

assume that fuel productivity comparisons are made between new vehicles.

Table 3-12 shows fuel productivity estimates for size-limited 5- and 6-axle
tractor- semitrailers, Twin 28s, Rocky Mountain Doubles, and Turnpike Doubles
Fuel productivity for size-limited Twin 28s slightly decreases with increasing
axles. This is because at a constant freight density, Twin 28s carry the same
payload weight without regard to the number of axles on the vehicle. But as
the number of axles increase the empty weight and total weight of the vehicles
increase without a payload gain As weight increases MPG decreases while
payload remains constant, So, fuel productivity decreases as the number of

axles increase. However, the fuel productivity benefits from shifting to


INTERCEP

1 000
-0 6330
0 6619
-0 9542,
-0 2244
-0 0881
2 0459

--- EEA GVW Group=60,009-80,000 Lbs Type of fuel used by vehicle-Dieset ~~

Source

Model
Error
€ Total

Root MSE
Dep Meen
cv

Variable DF

INTERCEP.
MOLIDK
LaTwoT 1
LaecTR
DLOCAL
DAERO
BECO

MOL iDx

-0 6330
1 0000
-0 1003
-9 0354
0 1615
-0 1792
-0 0967

MODEL 7
Dependent Variable: LGPM

Analyele of Vartence

Correlation of Estimates

Lerrwor LEPCTR
0 6619 +0 03542
-0 1004 -0 0331
1 0000 -0 1030
+9 1059 3 9000
0 1805 © 1011
0 0624 0 0392
0 0106 0 0157

Mean
OF F Vetue
6 50 93506 6.88931 379 903
17075381 99802 D 02233
1708) 432 49388
0 14949 R-squere o 1178
-1 63480 Adj R-ag 01175
79 14399
Parameter Estimates
Parenotor Standard = T for RO
Eaticate Error Perameter:
-1 958636 = 9 00215392 ~asz 6ce
-0 0112019 CoD36188 -10 959
0 g'2623 9 00375790 7 aor
0 411280 g OO723494 15 381
0 925469 =o BOZ93003 a 69a
-0 p1bDeB = (00426924 2
-0 927505 =o 00473327 “san

DLOCAL

-0 2244
0 1615
0 1005
p11)
1 9000
© 0812
0 0073

Probe
© 0000

-O 0882
-O 1792
“0 0626
D 0992
0.0012
1 0000
-0.7230



2, HEAVY-DUTY TRUCK FLEET CHARACTERISTICS

2.1 INTRODUCTION

The term "heavy-duty" truck encompasses a wide range of weights and operating
characteristics of trucks used in on-highway operations. Trucks with a Gross
Vehicle Weight (GVW) higher than 8,500 lbs are considered by EPA as heavy-
duty. This rating gives the low end of the heavy-duty GVW spectrum, while the
maximum rating allowed for on-highway tractor-trailers is 80,000 lbs.
Industry, on the other hand, classifies the market differently. Until
recently, all trucks with a GVW rating of 10,000 lbs or less were regarded as
light-duty. However, this definition has changed to include trucks with a GVW
rating to 14,000 lbs, as premium versions of models rated above 10,000 lbs
have been introduced in the 10,000 to 14,000 GVW range. In industry terms,
this range is referred to as Class 3, and is a new market where few trucks
were sold previously Trucks in Class 4 (14,001 to 16,000 lbs) and Class 5
(16,001 to 19,500 lbs) were also limited in sales until recently

Trucks in Class 6 (19,500 to 26,000 lbs) and Class 7 (26,000 to 33,000 lbs)
are typically referred to by industry as medium-heavy-duty trucks. Class 8
trucks include those trucks with GVW ratings between 33,000 and 80,000 lbs.
However, the lower weight range of Class 8 trucks shares many of the
characteristics of medium-heavy-duty trucks To assure that these common
vehicle characteristics are accounted for, EEA found it necessary to
disaggregate Class 8 into two sub-categories. Class 8A includes those trucks
with GVW ratings from 33,001 to 60,000 lbs, and Class 8B refers to those
trucks with GVW ratings from 60,001 to 80,000 lbs. Class 8A trucks are also
considered to be medium-heavy-duty, or ‘super-mediums’ in industry terms,

while trucks in Class 8B are referred to as heavy-heavy-duty

This section presents fleet characterization data for the medium-heavy-duty
and heavy-heavy-duty truck markets (i.e, Classes 6 to 8B). Such data analysis

is integral in understanding technological and policy effects on fuel


Pumping loss is not a large fraction of total output for diesel engines,
Mercedes estimated pumping loss to be equivalent to half of friction loss at
full load. At a given RPM, engine absolute pumping loss is not a strong
function of load, and therefore is a larger factor at light loads, much like
friction. Pumping loss can be reduced by controlling airflow through the
engine to prevent "excess" air due to turbocharger mismatch at different
speeds and loads. In addition, the use of pulse-tuned intake manifolds and
tuned exhausts can reduce pumping loss at specific load/speed points. These
technologies provide very small benefits in fuel economy, and have been widely
adopted in most heavy-heavy engines. Variable volume intake and exhaust
systems have not been considered for heavy-duty diesels, due to their poor

cost/benefit.

The use of 4-valve heads reduces the pressure drop across the valve orifice,
and is common in many of domestic heavy-heavy engines However, most of the
engines rated below 270 HP, and most imports of all horsepower ratings, use
2-valve engines. Conversion to 4-valve aids in reducing the pumping loss, and
also in increasing the bmep of a specific engine. BMEP increases are,

however, accounted for separately in the analysis.
Reductions in pumping loss in total over the next 10 years are likely to be
less than 5 percent in medium-heavy duty engines. This translates into a half

percent increase in fuel economy

The net benefit from all improvements to conventional diesel engines will vary

by engine type, as the heavy-duty diesels (used in Class 8B trucks) already
incorporate technology that the lighter engines do not. A summary of the
potential gains is provided in Table 4-6. In 1991, virtually all of the
heavy-heavy-duty engines feature air-to-air intercooling and some already are
of the high BMEP design As shown in Table 4-6, a 7,5 percent improvement to
bsfc is forecast over the period 1987-2001 relative to a 1987 baseline, at

constant emission standards. The imposition of the 5 0 g/BHP-hr standard in


payload weight is the difference between the vehicle's empty weight and 80,000
lbs (maximum legal operating weight). This GVW limit constrains the
maximization of fuel productivity for many carriers. At this, or any other,
weight limit there is a freight density at which weight capacities are fully
utilized. This is referred to as the optimum density. For finely divisible
commodities, such as liquids, it is possible to load a vehicle to its optimum
capacity. But for many other products, the 80,000 lbs GVW cap results in the
inability to use some portion of the vehicle's potential capacity by
restricting the weight of the items being shipped. To the extent that freight
hauled is more than the optimum density, weighing-out situations occur. The
80,000 lbs capacity is reached before the alternative capacity can be
realized. Such unused capacity is an opportunity cost that motor carriers

must incur. This cost can be metered by losses in fuel productivity.

In this study, EEA investigates the fuel productivity effect of eliminating
the 80,000 lbs GVW cap. Under this scenario, GVW would be controlled by
weight limits set by the application of Bridge Formula B and by current axle-
weight limits. It is assumed that no changes in state length limits take
place, This policy would have no effect on those configurations that are
limited im GVW by current axle-weight limits, such as, straight trucks, 4-axle
tractor-combinations, and 5-axle tractor-combinations. Of course, other
policy options are available regarding weight regulations (and have been
studied extensively), such as redefining the bridge formula or changing axle-
weight limits However, such proposals are more difficult to quantify in a

systematic fashion and are beyond the scope of this study.

When both conventional tractor-semitrailers, 5-axle Twin 28s, and 7- to 9-axle
Twin 28s are limited to 80,000 lbs, the 7- to 9-axle Twin 28s are much less
productive because of their higher empty weights. Weight-limited carriers are
better off operating 5-axle tractor-semitrailers since more payload can be
carried, while size-limited carriers are better off operating 5-axle Twin 28s
that are lighter and more fuel efficient. Under an uncapped Bridge Formula B
scenario, 7-axle, 8-axle, or 9-axle Twin 28 operators would not need special
permit to operate beyond 80,000 lbs GVW A policy that eliminates the 80,000

3-11


automatic transmission can be less efficient than a manual transmission that
is shifted correctly, actual driver behavior may make the automatic transmis-

sion more efficient in certain applications.

Drivetrain component suppliers are also integrating their axle and transmis-
sion/clutch offering, partly in response to a narrowing of the supplier base
for each manufacturer. In the past, consumers could specify clutch, transmis-
sion and axles from different suppliers with some loss of configuration
optimization. The bundling of those components could result in an improvement

in drivetrain optimization.

It is difficult to estimate the benefits of drivetrain optimization, as the
current extent of misspecification is not well understood. In addition the
benefit of some improvements is dependent on driver behavior that is common
now, not on what it will be in the future. We have relied on manufacturer
opinions to estimate the fleet average benefits by truck class and city-

highway cycle, as follows, in terms of percent improvements to MPG

City Highway
Class 6/7 20 20
Class 8A 1.5 1.5
Class 8B 1.5 2.0

These benefits do not include any benefit associated with low RPM engines for

Class 6/7/8A trucks

4.9 ELECTRONIC CONTROL

Electronic controls are being widely incorporated into trucks, partly in
response to new emission standards that are easier to meet with these
controls. In 1987, very few trucks had any electronic controls, but in 1990
industry experts stated that about 20 percent of Class 8B trucks and 5 percent
of medium duty (Class 6/7/8A) trucks had electronic control As noted,

electronic controls of fuel injection does not improve the bsfc of the engine


VARIABLE,
Bee w3)

MODELYR

EMAGET
AVWGET

ANNMIL
PNOLOD

AREAOP

PCARSZ

cID

HRSPHR

AERODN
ECOENG

TABLE 3-3
DEFINITIONS OF TIUS VARIABLES

USED IN THE ANALYSIS

DEEINIrIon

The number of miles-per-gallon that the vehicle averaged during 1987

The model year of the vehicle, ranging from 1987 to 1976 Model year 1976 includes all
pre-1976 model years as well

The empty, or tare, waight of the vehicle expressed in tons

‘The average woight (empty woight plus weight of cargo), expressed in tons, of a vehicle
when carrying a typical payload

Tho number of miles that the vehicle was driven during 1987

The approximate percentage of the vehicle’s annual mil
cargo, was carried

@ that that no payload, or

The area of operation of the vehicle AREAOP will be take on the following numbers if
the particular condition 1s met

AREAOP=1 1f the vehicle's greatest percentage of miles traveled were off-road
AREAOP=2 if the vehicle's greatest percentage of miles traveled wore within a 50
mile radius of the vehicle's home base

AREAOP=3 if the vehicle's greatest percentage of miles traveled were within a 50
to 200 mle radius of homebase

AREAOP=4 1f the vehicle's greatest percentage of miles traveled were beyond a 200
mile radius from home base

The approximate percentage of annual miles that the vehicle carried payloads that filled
its maximum cargo size This variable can be used as an index for the cube-out rato of
the vehicle

The approximate percentage of annual miles that the vehicle carried payloads that filled
its maximum cargo weight This variable can be used as an index for the weigh-out rate
of the vehicle

The size of the vehicle’s engine, 1n cubic inches Rather than an actual number, a
ranged coding scheme 1s used whereby the responder provides the range in which the
vehicle's engine size falls

The horsepower rating of the vehicle's engine As with CID, rather than an actual
number, a ranged coding schome 1s used whereby the responder provides the range in which
the vehicle's horsepower rating falls

AERODN|1 if the vehicle has aerodynamic features

ECOENG=1 if the vehicle has a fuel economy engine with low RPM, high torque cise,
turbocharger, etc