# Title 40

## SECTION 1037.805

### 1037.805 Symbols, abbreviations, and acronyms.

§ 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:

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:

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 | |||

a | atomic hydrogen-to-carbon ratio | mole per mole | mol/mol | 1. |

a | axle position regression coefficient | |||

a0 | intercept of air speed correction | |||

a1 | slope of air speed correction | |||

ag | acceleration of Earth's gravity | meters per second squared | m/s ^{2} |
m·s−2. |

a0 | intercept of least squares regression | |||

a1 | 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 | |||

b | atomic oxygen-to-carbon ratio | mole per mole | mol/mol | 1. |

b | axle position regression coefficient | |||

b0 | intercept of air direction correction | |||

b1 | 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/mph ^{2} or N·s
^{2}/m ^{1} |
kg·m−1. |

c | axle position regression coefficient | |||

ci | axle test regression coefficients | |||

Ci | constant | |||

ΔCdA | differential drag area | meter squared | m ^{2} |
m ^{2}. |

CdA | drag area | meter squared | m ^{2} |
m ^{2}. |

Cd | drag coefficient | |||

CF | correction factor | |||

Crr | coefficient of rolling resistance | kilogram per metric ton | kg/tonne | 10−2. |

D | distance | miles or meters | mi or m | m. |

e | mass-weighted emission result | grams/ton-mile | g/ton-mi | g/kg-km. |

Eff | efficiency | |||

F | adjustment factor | |||

F | force | pound force or newton | lbf or N | kg·m·s−2. |

fn | 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/s ^{2} |
m·s−2. |

h | elevation or height | meters | m | m. |

i | indexing variable | |||

ka | drive axle ratio | 1 | ||

kd | transmission gear ratio | |||

ktopgear | 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. |

Me | vehicle effective mass | kilogram | kg | kg. |

Mrotating | inertial mass of rotating components | kilogram | kg | kg. |

N | total number in series | |||

n | number of tires | |||

n | amount of substance rate | mole per second | mol/s | mol·s−1. |

P | power | kilowatt | kW | 10 ^{3}·m
^{2}·kg·s−3. |

P | tire inflation pressure | pascal | Pa | kg·m−1·s−2. |

p | pressure | pascal | Pa | kg·m−1·s−2. |

r | mass density | kilogram per cubic meter | kg/m ^{3} |
kg·m−3. |

PL | payload | tons | ton | kg. |

f | direction | degrees | ° | °. |

1 | direction | degrees | ° | °. |

r | tire radius | meter | m | m. |

r
^{2} |
coefficient of determination | |||

Re# | Reynolds number | |||

SEE | standard estimate of error | |||

s | 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 | m ^{2}·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·m
^{2}·kg·s−1. |

wC | 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 to define a quantity:

Superscript | Quantity |
---|---|

overbar (such as y ) | arithmetic mean. |

Double overbar (such | arithmetic mean of |

= | arithmetic mean. |

as y) | |

overdot (such as y ) | quantity per unit time. |

(d) *Subscripts.* This part uses the following subscripts
to define a quantity:

Subscript | Quantity |
---|---|

±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:

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. |

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. |

rpm | revolutions per minute. |

SAE | Society of Automotive Engineers. |

SEE | standard error of 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:

Symbol | Quantity | Value |
---|---|---|

g | gravitational constant | 9.81 m·s−2. |

R | specific gas constant | 287.058 J/(kg·K). |

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

Symbol | Quantity | Value |
---|---|---|

µ | micro | 10−6 |

m | milli | 10−3 |

c | centi | 10−2 |

k | kilo | 10 ^{3} |

M | mega | 10 ^{6} |