Symbols, abbreviations, and acronyms.

  1. Law
  2. CFR 40
  3. Protection of Environment
  4. Environmental Protection Agency
  5. Air Pollution Controls
  6. Control of Emissions from New Heavy-Duty Motor Vehicles
  7. Definitions and Other Reference Information
  8. Symbols, abbreviations, and acronyms.

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§ 1037.805 Symbols, abbreviations, and acronyms.

The procedures in this part generally follow either the International System of Units (SI) or the United States customary units, as detailed in NIST Special Publication 811 (incorporated by reference in § 1037.810). See 40 CFR 1065.20 for specific provisions related to these conventions. This section summarizes the way we use symbols, units of measure, and other abbreviations.

(a) Symbols for chemical species. This part uses the following symbols for chemical species and exhaust constituents:

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Symbol Species
C carbon.
CH4 methane.
CO carbon monoxide.
CO2 carbon dioxide.
H2O water.
HC hydrocarbon.
NMHC nonmethane hydrocarbon.
NMHCE nonmethane hydrocarbon equivalent.
NO nitric oxide.
NO2 nitrogen dioxide.
NOX oxides of nitrogen.
N2O nitrous oxide.
PM particulate matter.
THC total hydrocarbon.
THCE total hydrocarbon equivalent.

(b) Symbols for quantities. This part uses the following symbols and units of measure for various quantities:

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Table 2 to § 1037.805 - Symbols for Quantities

Symbol Quantity Unit Unit symbol Unit in terms of SI
base units
A vehicle frictional load pound force or newton lbf or N kg·m·s−2.
a axle position regression coefficient.
α atomic hydrogen-to-carbon ratio mole per mole mol/mol 1.
α axle position regression coefficient.
α0 intercept of air speed correction.
α1 slope of air speed correction.
αg acceleration of Earth's gravity meters per second squared m/s2 m·s−2.
α0 intercept of least squares regression.
α1 slope of least squares regression.
B vehicle load from drag and rolling resistance pound force per mile per hour or newton second per meter lbf/(mi/hr) or N·s/m kg·s−1.
b axle position regression coefficient.
β atomic oxygen-to-carbon ratio mole per mole mol/mol 1.
β axle position regression coefficient.
β0 intercept of air direction correction.
β1 slope of air direction correction.
C vehicle-specific aerodynamic effects pound force per mile per hour squared or newton-second squared per meter squared lbf/mph2 or N·s2/m2 kg·m−1.
c axle position regression coefficient.
c i axle test regression coefficients.
C i constant.
ΔCdA differential drag area meter squared m2 m2.
C d A drag area meter squared m2 m2.
C d drag coefficient.
CF correction factor.
C rr coefficient of rolling resistance kilogram per metric ton kg/tonne 10−3.
D distance miles or meters mi or m m.
e mass-weighted emission result grams/ton-mile g/ton-mi g/kg-km.
Eƒƒ efficiency.
F adjustment factor.
F force pound force or newton lbf or N kg·m·s−2.
f n angular speed (shaft) revolutions per minute r/min π·30·s−1.
G road grade percent % 10−2.
g gravitational acceleration meters per second squared m/s2 m·s−2.
h elevation or height meters m m.
i indexing variable.
k a drive axle ratio 1.
k d transmission gear ratio.
k topgear highest available transmission gear.
L load over axle pound force or newton lbf or N kg·m·s−2.
m mass pound mass or kilogram lbm or kg kg.
M molar mass gram per mole g/mol 10−3·kg·mol−1.
M vehicle mass kilogram kg kg.
M e vehicle effective mass kilogram kg kg.
M rotating inertial mass of rotating components kilogram kg kg.
N total number in series.
n number of tires.
ṅ amount of substance rate mole per second mol/s mol·s−1.
P power kilowatt kW 103·m2·kg·s−3.
p pressure pascal Pa kg·m−1·s−2.
ρ mass density kilogram per cubic meter kg/m3 kg·m−3.
PL payload tons ton kg.
φ direction degrees ° °.
c direction degrees ° °.
r tire radius meter m m.
r 2 coefficient of determination.
Re# Reynolds number.
SEE standard error of the estimate.
σ standard deviation.
TRPM tire revolutions per mile revolutions per mile r/mi.
TRRL tire rolling resistance level kilogram per metric ton kg/tonne 10−3.
T absolute temperature kelvin K K.
T Celsius temperature degree Celsius °C K-273.15.
T torque (moment of force) newton meter N·m m2·kg·s−2.
t time hour or second hr or s s.
Δt time interval, period, 1/frequency second s s.
UF utility factor.
v speed miles per hour or meters per second mi/hr or m/s m·s−1.
w weighting factor.
w wind speed miles per hour mi/hr m·s−1.
W work kilowatt-hour kW·hr 3.6·m2·kg·s−1.
w C carbon mass fraction gram/gram g/g 1.
WR weight reduction pound mass lbm kg.
x amount of substance mole fraction mole per mole mol/mol 1.

(c) Superscripts. This part uses the following superscripts for modifying quantity symbols:

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Table 3 to § 1037.805 - Superscripts

Superscript Meaning
overbar (such as ȳ) arithmetic mean.
Double overbar (such as y) arithmetic mean of arithmetic mean.
overdot (such as ẏ) quantity per unit time.

(d) Subscripts. This part uses the following subscripts for modifying quantity symbols:

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Table 4 to § 1037.805 - Subscripts

Subscript Meaning
±6 ±6° yaw angle sweep.
A A speed.
air air.
aero aerodynamic.
alt alternative.
act actual or measured condition.
air air.
axle axle.
B B speed.
brake brake.
C C speed.
Ccombdry carbon from fuel per mole of dry exhaust.
CD charge-depleting.
circuit circuit.
CO2DEF CO2 resulting from diesel exhaust fluid decomposition.
CO2PTO CO2 emissions for PTO cycle.
coastdown coastdown.
comp composite.
CS charge-sustaining.
cycle test cycle.
drive drive axle
drive-idle idle with the transmission in drive.
driver driver.
dyno dynamometer.
effective effective.
end end.
eng engine.
event event.
fuel fuel.
full full.
grade grade.
H2Oexhaustdry H2O in exhaust per mole of exhaust.
hi high.
i an individual of a series.
idle idle.
in inlet.
inc increment.
lo low.
loss loss.
max maximum.
meas measured quantity.
med median.
min minimum.
moving moving.
out outlet.
P power.
pair pair of speed segments.
parked-idle idle with the transmission in park.
partial partial.
ploss power loss.
plug-in plug-in hybrid electric vehicle.
powertrain powertrain.
PTO power take-off.
rated rated speed.
record record.
ref reference quantity.
RL road load.
rotating rotating.
seg segment.
speed speed.
spin axle spin loss.
start start.
steer steer axle.
t tire.
test test.
th theoretical.
total total.
trac traction.
trac10 traction force at 10 mi/hr.
trailer trailer axle.
transient transient.
TRR tire rolling resistance.
urea urea.
veh vehicle.
w wind.
wa wind average.
yaw yaw angle.
ys yaw sweep.
zero zero quantity.

(e) Other acronyms and abbreviations. This part uses the following additional abbreviations and acronyms:

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Table 5 to § 1037.805 - Other Acronyms and Abbreviations

Acronym Meaning
ABT averaging, banking, and trading.
AECD auxiliary emission control device.
AES automatic engine shutdown.
APU auxiliary power unit.
CD charge-depleting.
CFD computational fluid dynamics.
CFR Code of Federal Regulations.
CITT curb idle transmission torque.
CS charge-sustaining.
DOT Department of Transportation.
ECM electronic control module.
EPA Environmental Protection Agency.
FE fuel economy.
FEL Family Emission Limit.
GAWR gross axle weight rating.
GCWR gross combination weight rating.
GEM greenhouse gas emission model.
GVWR gross vehicle weight rating.
Heavy HDV Heavy heavy-duty vehicle (see § 1037.140).
HVAC heating, ventilating, and air conditioning.
ISO International Organization for Standardization.
Light HDV Light heavy-duty vehicle (see § 1037.140).
Medium HDV Medium heavy-duty vehicle (see § 1037.140).
NARA National Archives and Records Administration.
NHTSA National Highway Transportation Safety Administration.
PHEV plug-in hybrid electric vehicle.
PTO power take-off.
RESS rechargeable energy storage system.
SAE Society of Automotive Engineers.
SEE standard error of the estimate.
SKU stock-keeping unit.
TRPM tire revolutions per mile.
TRRL tire rolling resistance level.
U.S.C. United States Code.
VSL vehicle speed limiter.

(f) Constants. This part uses the following constants:

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Table 6 to § 1037.805 - Constants

Symbol Quantity Value
g gravitational constant 9.80665 m·s−2.
R specific gas constant 287.058 J/(kg·K).

(g) Prefixes. This part uses the following prefixes to define a quantity:

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Symbol Quantity Value
µ micro 10−6
m milli 10−3
c centi 10−2
k kilo 103
M mega 106

[81 FR 74048, Oct. 25, 2016, as amended at 86 FR 34492, June 29, 2021]


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