**UNITED STA TES**  **ENVIRONMENTA L PROTECTION A** **GENCY** NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY

2565 PLYMOUTH ROAD ANN ARBOR, MI 48105
- 2498

OFFICE OF AIR AND RADIATION 

### May 27, 2015 MEMORANDUM SUBJECT: Vocational Vehicle Aerody namic Testing Program FROM: Lauren Steele , Environmental Engineer, OTAQ/ASD TO: Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium

- and Heavy- Duty

Engines and Vehicles

- Phase 2

- Docket EPA
- HQ
- OAR
- 201 4
- 0827 **Introduction** This memorandum describes a possible approach that EPA and NHTSA could use to recognize the fuel efficiency

and GHG emission improv ements from use of aerodynamic devices on vocational vehicles as part of the Phase 2 program. The data summarized below are from work completed as of March 2015 under an agreement with the California Air Resource Board (ARB) the National Renewable Energy Laboratory

(NREL)
. NREL performed a series of coastdown tests on heavy

- duty vocational vehicles with and without aerodynamic improvement devices to assess their performance. Excerpts of progress reports from which this summary is derived are attached as an appendix to this memorandum. The devices tested were not intended to include all aerodynamic devices available for vocational vehicles, rather they

are a sampling of the most common ty pes of technologies that are currently commerciall y available. Recognition of vocational aerodynamic technology within the Phase 2 GHG program would not need to be based solel y on data obtained through this ARB
-NREL agreement. Should other data become available, it would be taken into consideration as well. **Background** The vast majority

of aerody

namic improvement technologies that have been evaluated through U.S. EPA’s SmartWay

program and for compliance with the Phase 1 heavy

- duty vehicle greenhouse gas standards have been devices primaril y intended for heavy- duty Class 8 tractor

- trailers. There is a data gap regarding the potential benefits of aerodyn amic improvement technologies for use on heavy- duty vocational vehicles. ARB staff gathered information about aerodynamic controls for this vehicle category though literature reviews and stakeholder discussions prior to initiating the NREL study under ARB Agreement Number 11

- 600, NREL Contract Number FIA

- 12
- 176 3. It is the intention of this current NREL study to complement previous work and explore the potential benefits of the most common aerodynamic improvement devices on box trucks using both coastdown and on

- road steadystate techniques. The testing utilized two common vocational vehicle designs, a Class 4 and a Class 6 box truck, which often operate at duty cycles with sufficient high

- speed operation where aerodynam ic

### 2

devices could provide significant fuel savings. The overall intent of the NRELwork is to estimate the expected benefits of several common ty pes of vocational aerodyn amic devices, as accuratel y as possible given limited test time and budget. **Summary of NREL Test Program** Table 1 

### compares some features of the two heavy

- duty vocational vehicles were that w ere tested and measured by

NREL. **Table 1**  **: Truck Descriptions Vehicle Descriptor**  **Class 6 Box Truck Class 4 Box**  **Truck** Cab Style Conventional Low Cab Forward GVWR 26,000 lbs 14,500 lbs Nominal Box Length 26 feet 16 feet Full Vehicle Length 37 feet 23 feet Full Vehicle Height 12 ft 10 inches 11 feet Average Widtha 8 ft 4 inches 8 feet 1 inch Minimum Ground Clearance 10 inches 5 inches Note: a This calculation made by EPA not NREL 

### The NREL team evaluated the performance of three aerodyn amic devices on the Class 6 truck and one device on the Class 4 truck, as shown in Table 2
. Images of aerodynamic devices tested can be found in the Appendix to this document. **Table 2**  **: Vocational Aerodynamic Te chnologies Assessed**  VEHICLE BOX CHASSIS SKIRTS FRONT (ROOF)

FAIRING REAR

FAIRING WHEEL

COVERS Class 6 Box Truck X X X Class 4 Box Truck X Device Weight (lbs) 101 34 109 5 

### Coastdown testing was performed following the guidelines from SAE J1263, “Road Load Measurement and Dy

namometer Simulation Using Coastdown Techniques” and SAE J2263, “Road Load Measurement Using Onboard Anemometry and Coastdown Techniques” with the additio nal calculation step of normalizing the results to STP from 40 CFR §1066.310

- 4. Table 3 

### presents preliminary

coastdown results, which have been correct ed for road grade, headwind/tailwind , air temperature , and air pressure. The NREL results are preliminary, wherea s planned future work under the ARB agreement includes repeated coastdown tests, steady

- state tests, and further analysis of the data and refin ement of the processing code.

### 3 **Table 3**  **: Preliminary Coastdown Results VEHICLE**  **TYPE CONFIGURATION**  **C D** * **A [ m**  **2 ]**  **a DELTA**  **C D**  ***** **A [**  **m 2**  **] b** 

Class 6 Box Truck Reference Average 5.64
-

With Chassis Skirt 4.86 0.82 With F ront F airing 5.24 0.52 With Chassis Skirt & Front F airing 5.16 0.60 With Wheel Covers 5.34 0.03 With Chassis Skirt, F ront F airing, and Wheel Covers 5.25 0.49 c Class 4 Box Truck Reference 5.28
-

With Rear Fairing 5.01 0.27 Notes: a Central values are presented for C D A and D elta C D A. See appendix for high/low estimates. b Changes in C D A ( delta s ) are determined for each device using separate baseline test run s , not the average of the reference runs shown here
. c Crosswind conditions on this test date put these results in question. 

### Possible **Phase 2 Approach to Vocational Aerodynamics** The agencies are considering adopting provisions in the Phase 2 HD GHG program to enabl e chassis manufacturers to obtain credit for installation of aerodyn amic devices on vocational vehicles. One potential approach is to offer delta C D

### A value s as optional input s in the GEM simulation tool associated with certain aerodynamic devices . M anufacturers who install (or instruct another entity to install) an eligible device on an eligible vehicle w ould select the appropriate input and GEM would apply the pre - defined delta C D

### A to the default C D

### A that is already programmed in GEM for the applicable vehic le weight class. F or such an approach to be practical , the agencies believe this would require that the certifying manufacturer have knowledge of and some degree of control over the size and shape of the vehicle in its final built form. To address cases where business relationships or other factors enable chassis manufacturers to do this, the agencies are proposing delegated assembly provisions in the regulations. See 40 CFR 10 37.621
. If the agencies were to adopt this approach b ased on the preliminary NREL results, it would likely be necessary

to restrict eligibility

of vocational vehicles that could be certified with an improved C D

### A in GEM to those meeting the characteristics described in Table 4 below
. If additional data b ecome available to the agencies, quantifying the effect of changes in vehicle frontal area and /or length on delta C D

### A for specific devices , the vehicle siz e eligibility could be broadened
. To ensure that vehicles applying for this credit would be most likely to benefit from aerody

namic technology

in the real world, the agencies may

choose to restrict eligible vehicles to those that meet the segmentation criteria in 40 CFR 1037. 510(c) specifying certifi cation using the Regional duty cycle in GEM.

### 4

**Table 4**  **: Characteristics of Vehicles Potentially Eligible to**  **Gain GEM Credit**  **for Aerodynamics** VEHICLE TYPE GVWR CHASSIS LENGTH FRONTAL AREA Low Cab Forward Box Truck 1 0 ,001 to 19 , 5 00 lb (Class 3

- 5) 7 m (+

- 0.3 m) 8 .0 m2 (+

- 0.2 m2 ) Conventional Cab Box Truck 1 6 ,001 lb to 33 ,000 lb (Class 5

- 7) 1 1 m (+

- 0.3 m) 9
. 3 m2 (+

- 0.2 m2 ) 

### The frontal areas in Table 4 are based on calculations using measurements of vehicle dimensions from NREL that are found in the appendix plus other dimensions transmitted to the ARB and EPA during this project
. Th e formula specified in SAE J1263 (used with light

- duty vehicles) where f rontal area is estimated by multiplying the total vehicle height and the maximum vehicle width b y 80 percent, was not used . If that protocol had been used, the resulting estimates of frontal area would have been 7.0 m2 

### for the low cab forward truck and 8.1 m2 

### for the conventional ca b truck versus 8.0 m2 

### and 9.3 m2 

### , respectivel y, from Table 4. Based on the preliminary NRELresults , the agencies are considering a narrow range of eligible aerodynamic devices : box chassis skirts and front (roof) fairings for larger trucks ; and rear fairings (tails) for smaller trucks
. Depending on additional data that may become available to the agencies during the comment period, quantifying the effect of different devices on delta C D

### A for specific vehicles, the device eligibility could be broadened
. Table 5 presents some ranges of possible delta C D

### A values ( derived from Table 3), which could be in the range of pre - defined technology improvement v alues made available in GEM under certain circumstances
.

**Table 5**  **: Possible**  **Aerodynamic Technolog y**  **Improvement Values**  **( Delta**  **C D** **A, m**  **2 )** 

BOX CHASSIS SKIRTS FRONT

FAIRING FRONT FAIRING

A ND SKIRTS REAR

FAIRING Conventional Cab Box Truck (Class 5

- 7) 0.6 to 0.9 0.4 to 0.6 0.5 to 1.0
- Low Cab Forward Box Truck (Class 3

- 5) - - - 0.1 to 0.4 Certification Conditions Regional duty cycle, Delegated assembly agreement


### To illustrate the effect on vehicle fuel efficiency reflected in GEM of changes in a vocational vehicle’s C D

### A, the agencies have simulated some example effectiveness values for the following combinations of devices and vehicles: a LHD vocational vehicle with only a rear fairing and both a chassis skirt and a front fairing; and a MHD vocational vehicle with only a front fairing and both a chassis skirt and a front fairing. These cases are shown in Table 6
.

### 5 **Table 6**  **: Vehicle Cases Simulated in GEM** VEHICLE TECHNOLOGY WEIGHT IN LBS EXAMPLE DELTA C DA (m2 ) Light heavy

- duty vocational vehicle (Class 3

- 5) Rear Fairing 109 0.2 Chassis Skirts & Front Fairing 135 1.0 Medium heavy

- duty vocational vehicle (Class 6

- 7) Front Fairing 34 0.4 Chassis Skirts & Front Fairing 135 1.0


### Each of these cases was run in GEM twice: once ignoring the added weight of the device and a second time adding the weight of the device, as reported by NREL. This is done for illustrative purposes, to show the likely effects of added weight on the simulated vehicles in GEM . Physics would suggest that added mass m ay cause the overall effectiveness of an aerodyn amic device to be diminished by varying amounts depending on the driving patterns of a vehicle. The results in Table 7 

### represent technology effectiveness where the mass of the aerody namic device has been disregarded. The results in Table 8 represent technology effectiveness where the mass of the aerodynamic device has been taken into account by allocating half to the static test weight and half to a diminished payload. In the results presented below, some of the cases involve the same combination of technologies

- chassis skirt and front fairing

- on both a LHD vehicle and a MHD vehicle. The differences in these results reflect the differences in the vehicle parameters in GEM , including a different engine, transmission, chassis weight and payl oad. In comparing these cases , it appears the LHD v ehicle benefits more from the aerodyn amic technology than the MHD vehicle does, though it also appears to be more sensitive to changes in weight.

### 6 **Table 7**  **: Example GEM Improvements Vocational Aerodynamics Effectiveness**  **Disregarding Weight Effects MEDIUM HEAVY**  **- DUTY**  **LIGHT HEAVY -** **DUTY** Baseline Front Fairing Chassis Skirt & Front Fairing Baseline Rear Fairing Chassis Skirt & Front Fairing C DA 5.4 5 4.4 5.4 5.2 4.4 65mph CO 2 Emission (g CO 2/ton

-mi ) 211 201 186 401 391 353 55mph CO 2 Emission (g CO 2/ton

-mi ) 171 164 153 314 308 280 Transient CO 2 Emission (g CO 2/ton

-mi ) 244 243 240 367 365 358 Effectiveness over 65 mph 4.5% 11.8% 2.4% 12.0% Effectiveness over 55 mph 4.1% 10.5% 2.2% 10.8% Effectiveness over Transient 0.6% 1.8% 0.5% 2.4% Regional Cycle Effectiveness (50% Transient, 28% 55 mph, 22% 65 mph) 2.3% 5.8% 1.3% 6.7% Multi

-Purpose Cycle Effectiveness (82% Transient, 15% 55 mph, 3% 65 mph) 1.2% 3.0% 0.8% 3.7% Urban Cycle Effectiveness (94% Transient, 6% 55 mph) 0.8% 2.1% 0.6% 2.7%

### 7 **Table 8**  **: Example GEM Improvements with Added Weight**  **Vocational Aerodynamics Effectiveness With Added Device Weight**  **MEDIUM HEAVY -** **DUTY LIGHT HEAVY** **- DUTY**  Baseline Front Fairing Chassis Skirt & Front Fairing Baseline Rear Fairing Chassis Skirt & Front Fairing C DA 5.4 5 4.4 5.4 5.2 4.4 Static Test Weight (kg) 11,408 11,416 11,439 7,257 7,282 7,288 Payload (ton s ) 5.60 5.59 5.57 2.85 2.82 2.82 65mph CO 2 Emission (g CO 2/ton

-mi ) 211 201 187 401 395 357 55mph CO 2 Emission (g CO 2/ton

-mi ) 171 164 154 314 311 284 Transient CO 2 Emission (g CO 2/ton

-mi ) 244 243 242 367 369 363 Effectiveness over 65 mph 4.5% 11.2% 1.4% 10.9% Effectiveness over 55 mph 4.1% 9.9% 1.2% 9.7% Effectiveness over Transient 0.6% 1.1%
- 0.6% 1.1% Regional Cycle Effectiveness (50% Transient, 28% 55 mph, 22% 65 mph) 2.1% 5.1% 0.3% 5.4% Multi

-Purpose Cycle Effectiveness (82% Transient, 15% 55 mph, 3% 65 mph) 1.0% 2.2%
- 0.3% 2.4% Urban Cycle Effectiveness (94% Transient, 6% 55 mph) 0.7% 1.4%
- 0.6% 1.4%

### 1 

## APPENDIX **Aerodynam ic Drag Reduction Technologies for Heavy** **- Duty Vocational** 

**Vehicles**

**– Preliminary Coastdown Results** 

### 2 January and February , 2015 

## Aerodynam**ic Drag Reduction Technologies for Heavy -** **Duty Vocational**

**Vehicles**

**– Preliminary Coastdown Results**  The National Renewable Energy L aboratory

(NREL) under ARB Agreement Number 11

- 600, NREL Contract Number FIA
- 1 1
- 1763 has performed a series of coastdown tests on heav y - duty vocational vehicles with and without aerodynamic i mprovement devices to assess their performance. These results are preliminary

and future work under this agreement will include additional repeats and stead y - state tests to help refine these results at a later date. The procedure used for coastdown testin g followed the general guidelines outlined in SAE J1263 and SAE J2263 and uses calculation from CFR 1066.310 where applicable. **Coastdown Track** The current coastdown track is located at the Front Range Airport east of Denver, CO. The east runway, which runs in a north

- south direction, has an access road along the east side of it. A portion of that road, as seen b y the red line in Figure 1, is used for coastdowns. The track runs in a north

- south direction. The southern end of the track has an average grade of 0.4%.

Track Profile

### 3

**Data Processing** Data is collected at 5Hz during the coastdown. An I SAAC data recorder monitors OBD information as well as logging velocity

from a Garmin 18x

- 5Hz which is used in the data post processing. Since the track has a slight grade the north and south profiles differ. 0 1 2 3 4 5 6 7 8**E l** **e v** **a t** **i o** **n C** **h a** **n g** **e [** **m e** **t e** **r s** **]**

**La titude**  North end of track Avg. 0.4% grade



## South **North**

### 4

The following road load equation is used to describe the behavior of the vehicle:

− ∆ h ∆ = + 1 2 At each time step interval the total force on the vehicle can be calculated using the following equation:

=

= −

∆ The effective mass (m e

### ) was calculated for the class 6 box truck by adding 56.7 kg to the measured vehicle mass for each tire making road contact. For the class 4 city van the ratio of rotating mass to measured vehicle mass was kept the same. After correcting for elevation change using the road grade survey each interval point in plotted and a least

- squares regression is used to determine the coefficients.

In the pol ynomial fit the ‘B’ term is fixed at zero and ‘A’ and ‘C’ coefficients are assigned as follows

=

= = 1 2 Then ‘D’ term can be corrected for standard conditions as follows

= 293 98
. 21

### 5

**The Vehicles**

### 6

### 7

**The Aerodynamic Devices Device**  **Vehicle Total Weight**  Wheel Covers 26’ Box Truck 2.2 kg (4.8 lbs) Front Fairing 26’ Box Truck 15.5 kg (34.1 lbs) Side Skirts 26’ Box Truck 45.9 kg (101 lbs) Rear Fairing 16’ LCF Truck 49.5 kg (109 lbs)

**Preliminary Results** All error estimates shown are 95% confidence intervals.

**Te st**  **Ve hi**  **cle Aero**  **dynami c**  **Device(s) A**  **m [lbf]**  **D adj**  **[lbf/mph 2**  **] μ**  **C d**  **A [m**  **2 ]**  **Ro ad Load @**  **55 mp**  **h [l bf]**  **Ro ad Load @** 

**45 mph [l**  **bf]** Cl ass 6 B ox Truck Base line (W heel Covers) 130. 2 ± 9. 2 0. 141 ± 0. 007 0. 0076 ± 0. 0005 5. 35 ± 0. 27 556 ± 14 415 ± 10 Cl ass 6 B ox Truck Whe el Cove rs 130. 8 ± 11 0. 142 ± 0. 006 0. 0076 ± 0. 0006 5. 42 ± 0. 21 562 ± 17 419 ± 13 Cl ass 6 B ox Truck Base line (Skirts) 144. 6 ± 17. 3 0. 158 ± 0. 011 0. 0085 ± 0. 001 6 ± 0. 43 622 ± 37 464 ± 27 Cl ass 6 B ox Truck Si de Ski rts 141. 2 ± 15. 2 0. 144 ± 0. 011 0. 0082 ± 0. 0009 5. 47 ± 0. 4 576 ± 43 432 ± 32 Cl ass 6 B ox Truck Base line (Fr ont Fai ri ng) 134. 7 ± 13. 8 0. 153 ± 0. 007 0. 0079 ± 0. 0008 5. 83 ± 0. 27 599 ± 18 445 ± 13 Cl ass 6 B ox Truck Front Fai ri ng 137. 4 ± 8 0. 14 ± 0. 006 0. 0081 ± 0. 0005 5. 32 ± 0. 21 560 ± 16 420 ± 12 Cl ass 6 B ox Truck Front Fai ri ng + Ski rts 125. 5 ± 10. 2 0. 136 ± 0. 005 0. 0073 ± 0. 0006 5. 18 ± 0. 19 538 ± 13 401 ± 9 Cl ass 6 B ox Truck Base line (All) 132. 7 ± 15 0. 15 ± 0. 009 0. 0078 ± 0. 0009 5. 72 ± 0. 34 588 ± 20 437 ± 15 Cl ass 6 B ox Truck Front Fai ri ng + Ski rts + Cove rs 137. 9 ± 7. 4 0. 138 ± 0. 004 0. 008 ± 0. 0004 5. 26 ± 0. 16 557 ± 10 418 ± 7 Cl ass 4 C it y Va n Base line (R ea r F ai ri ng) 126. 9 ± 3. 3 0. 139 ± 0. 003 0. 0128 ± 0. 0003 5. 29 ± 0. 12 548 ± 10 408 ± 7 Cl ass 4 C it y Va n Re ar Fai ri ng 124. 8 ± 6. 8 0. 133 ± 0. 005 0. 0125 ± 0. 0007 5. 05 ± 0. 2 526 ± 20 394 ± 15 

### Coe **ffi cients -** **In clude**  **s Corre**  **ct ion f**  **or Road Grade**  **a nd Ad** **justme nt**  **to Standard**  **Te mper** **ature and Pre**  **ssure**

### 8 **Observed Change Without Wind Correction** 

### Aero **dynami c**  **Device(s) μ**  **C d**  

### A **Ro ad Load**  **@ 5 5**  **mph Ro**  **ad Load**

**@ 4 5**  **mph** Wh eel Covers -0 .5 % ± 1. 2% -1 .3 % ± 1. 3% -1 .1 % ± 1. 1% -1 % ± 1% Si de Skirts 3. 4% ± 2. 1% 8. 8% ± 0. 8% 7. 3% ± 1. 3% 6. 8% ± 1. 2% Front Fai ri ng -1 .8% ± 1. 5% 8. 9% ± 0. 7% 6. 4% ± 1. 5% 5. 6% ± 1. 3% Front Fai ri ng + Sk irts 8. 7% ± 2. 2% 11. 2% ± 0. 8% 10. 2% ± 0. 9% 9. 9% ± 0. 8% Front Fai ri ng + Sk irts + Co ver s -3 .1 % ± 0. 9% 7. 9% ± 0. 8% 5. 3% ± 0. 6% 4. 4% ± 0. 5% Re ar Fai ri ng 1. 6% ± 0. 7% 4. 5% ± 0. 5% 3. 9% ± 0. 5% 3. 6% ± 0. 5%



### Obse **rve d Chang**  **e - Wi**  **thout Wind Corre**  **ct ion** 

**Te st**  **Vehicle Aero**  **dynami c Device(s)**  **A m**  **[l bf]**  **D adj**  **[lbf/mph 2**  **] μ**  **C d**  **A [m**  **2 ]**  **Ro ad Load @**  **55 mph [l**  **bf] Roa**  **d Load @**

**45 mph [l**  **bf]** Class 6 Box Truck Base line (W heel Covers) 129. 7 ± 8. 8 0. 141 ± 0. 009 0. 0075 ± 0. 0005 5.37 ± 0.34 556 ± 20 415 ± 15 Class 6 Box Truck Whe el Covers 128. 9 ± 15. 8 0. 14 ± 0. 008 0. 0075 ± 0. 0009 5.34 ± 0.29 553 ± 14 413 ± 11 Class 6 Box Truck Base line (Skirts) 141 ± 16. 1 0. 149 ± 0. 012 0. 0082 ± 0. 0009 5.68 ± 0.47 593 ± 28 444 ± 21 Class 6 Box Truck Si de Ski rts 146. 1 ± 22. 3 0. 128 ± 0. 014 0. 0085 ± 0. 0013 4.86 ± 0.54 533 ± 35 405 ± 26 Class 6 Box Truck Base line (Front Fairi ng) 136. 5 ± 12. 2 0. 151 ± 0. 007 0. 008 ± 0. 0007 5.76 ± 0.29 595 ± 15 443 ± 11 Class 6 Box Truck Front Fai ri ng 142. 4 ± 12. 1 0. 138 ± 0. 006 0. 0084 ± 0. 0007 5.24 ± 0.24 559 ± 19 421 ± 14 Class 6 Box Truck Front Fai ri ng + Ski rts 122. 8 ± 11 0. 136 ± 0. 007 0. 0071 ± 0. 0006 5.16 ± 0.26 533 ± 15 397 ± 12 Class 6 Box Truck Base line (All) 131. 9 ± 13. 9 0. 151 ± 0. 01 0. 0077 ± 0. 0008 5.74 ± 0.37 588 ± 21 437 ± 16 Class 6 Box Truck Front Fai ri ng + Ski rts + Co ver s 139. 4 ± 8. 9 0. 138 ± 0. 006 0. 0081 ± 0. 0005 5.25 ± 0.24 557 ± 14 419 ± 10 Class 4 Ci ty V an Base line (R ea r Fai ri ng) 126 ± 4 0. 139 ± 0. 005 0. 0127 ± 0. 0004 5. 28 ± 0. 2 546 ± 16 407 ± 12 Class 4 Ci ty V an Re ar Fai ri ng 129. 5 ± 4. 6 0. 132 ± 0. 008 0. 013 ± 0. 0005 5.01 ± 0.32 528 ± 25 396 ± 19 **Coe fficien**  **ts -**  **Inclu de**  **s Corre**  **ction fo**  **r Roa**  **d Grade**  **, He**  **adw ind/Tailwind and**  **Adjustme nt to**  **Standard Te mpe**  **rature and**  **Pre ssure**  **C onditions** 

### 9 **Observed Change With Wind Correction** 

### Aero **dynami c**  **De vice(s)**  **μ C**  **d** 

### A **Ro ad Load**  **@ 5 5**  **mph Ro**  **ad Load**

**@ 4 5**  **mph** Wh eel Covers 0. 6% ± 1. 4% 0. 5% ± 1. 4% 0. 6% ± 0. 4% 0. 6% ± 0. 5% Side Ski rts -2 .6% ± 1% 14. 5% ± 0. 8% 10. 2% ± 1. 2% 8. 8% ± 1. 1% Fr ont Fai ri ng -4 .1 % ± 1. 6% 9. 1% ± 0. 8% 6% ± 0. 7% 5% ± 0. 6% Fr ont Fai ri ng +S kirts 11. 8% ± 2. 1% 10. 5% ± 0. 8% 10. 4% ± 0. 8% 10. 3% ± 0. 7% Fr ont Fai ri ng +S kirts + C overs -4 .9 % ± 1% 8. 5% ± 0. 8% 5. 3% ± 0. 5% 4. 2% ± 0. 4% Re ar F ai ri ng -2 .8% ± 0. 7% 5. 2% ± 0. 5% 3. 3% ± 0. 3% 2. 7% ± 0. 3%



### Obse **rv ed**  **Change -** **With Wind Cor re**  **ction**

**Veh icle**  **Ae rodynam**  **ic D ev**  **ice(s )**  **Wind Speed [mph]**  **Wi nd N**  **Wind E Ai**  **r Temp [C ]**  **Atm P [ Bar**  **] Dew**  **Pt [ C]**  Cl as s 6 Bo x Truck Base lin e (W heel Cove rs ) 3. 4 0. 6 3. 2 12. 0 0. 828 -9 .0 Cl as s 6 Bo x Truck Whe el Cov er s 3. 5 1. 9 1. 1 13. 3 0. 828 -1 0. 2 Cl as s 6 Bo x Truck Base lin e (S ki rts) 8. 9 4. 4 5. 0 11. 5 0. 837 -6 .7 Cl as s 6 Bo x Truck Si de Skirts 8. 8 4. 5 1. 2 12. 6 0. 836 -7 .3 Cl as s 6 Bo x Truck Base lin e (F ront Fai ri ng) 3. 8 0. 6 -0 .5 14. 4 0. 832 -1 0. 3 Cl as s 6 Bo x Truck Front Fai ri ng 3. 3 -1 .0 -2 .7 15. 2 0. 832 -9 .6 Cl as s 6 Bo x Truck Front Fai ri ng + S ki rts 3. 4 1. 5 -2 .5 17. 8 0. 831 -9 .2 Cl as s 6 Bo x Truck Base lin e (All) 4. 7 0. 2 2. 9 11. 6 0. 834 -1 2. 2 Cl as s 6 Bo x Truck Front Fai ri ng + S ki rts + Cove rs 9. 2 0. 3 9. 1 14. 6 0. 833 -1 0. 9 Cl as s 4 C ity Va n Base lin e (R ea r Fai ri ng) 14. 1 0. 0 13. 9 6. 1 0. 834 -6 .5 Cl as s 4 C ity Va n Re ar Fai ri ng 13. 7 -3 .4 13. 1 6. 7 0. 833 -6 .0 

### Aver**age We**  **athe r Conditions** 

### 10

**Discussion** These results are preliminary and planned future work includes additional repeats and stead y - state tests. Also, data analys is efforts and refinement of the processing code are ongoing and may also affect future results. Under the test condition of “All* (s ee note)” please note that changing wind conditions shown in the weather conditions table for this test, predominately the eastern crosswind which increased dramatically between the baseline (all), and the test condition. This may have significantly affect ed this data point and the condition will be repeated once weather permits.