{"data":{"id":"us/40-cfr-1037.805","jurisdiction":"us","citation":"40 CFR 1037.805","heading":"Symbols, abbreviations, and acronyms.","body":"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, see § 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.\n(a) Symbols for chemical species. This part uses the following symbols for chemical species and exhaust constituents:\nTable 1 to Paragraph (a) of § 1037.805—Symbols for Chemical Species and Exhaust Constituents\nSymbol Species\nC carbon.\nCO carbon monoxide.\nCO2 carbon dioxide.\nH2 O water.\nHC hydrocarbon.\nNMHC nonmethane hydrocarbon.\nNMHCE nonmethane hydrocarbon equivalent.\nNO nitric oxide.\nNO2 nitrogen dioxide.\nNOX oxides of nitrogen.\nPM particulate matter.\nTHC total hydrocarbon.\nTHCE total hydrocarbon equivalent.\n(b) Symbols for quantities. This part 1037 uses the following symbols and units of measure for various quantities:\nTable 2 to Paragraph (b) of § 1037.805—Symbols for Quantities\nSymbol Quantity Unit Unit symbol Unit in terms of SI base units\nA vehicle frictional load pound force or newton lbf or N kg·m·s− 2.\na axle position regression coefficient\nα atomic hydrogen-to-carbon ratio mole per mole mol/mol 1.\nα axle position regression coefficient\nα0 intercept of air speed correction\nα1 slope of air speed correction\nag acceleration of Earth's gravity meters per second squared m/s2 m·s− 2.\na0 intercept of least squares regression\na1 slope of least squares regression\nB 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.\nb axle position regression coefficient\nβ atomic oxygen-to-carbon ratio mole per mole mol/mol 1.\nβ axle position regression coefficient\nβ0 intercept of air direction correction\nβ1 slope of air direction correction\nC 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.\nc axle position regression coefficient\nci axle test regression coefficients\nCi constant\nΔCd A differential drag area meter squared m2 m2.\nCd A drag area meter squared m2 m2.\nCd drag coefficient\nCF correction factor\nCrr coefficient of rolling resistance newton per kilonewton N/kN 10− 3.\nD distance miles or meters mi or m m.\ne mass-weighted emission result grams per ton-mile g/ton-mi g/kg-km.\nEff efficiency\nF adjustment factor\nF force pound force or newton lbf or N kg·m·s− 2.\nfn angular speed (shaft) revolutions per minute r/min π·30·s− 1.\nG road grade percent % 10− 2.\ng gravitational acceleration meters per second squared m/s2 m·s− 2.\nh elevation or height meters m m.\ni indexing variable\nka drive axle ratio 1.\nkd transmission gear ratio\nktopgear highest available transmission gear\nL load over axle pound force or newton lbf or N kg·m·s− 2.\nm mass pound mass or kilogram lbm or kg kg.\nM molar mass gram per mole g/mol 10− 3·kg·mol− 1.\nM vehicle mass kilogram kg kg.\nMe vehicle effective mass kilogram kg kg.\nMrotating inertial mass of rotating components kilogram kg kg.\nN total number in series\nn number of tires\nn amount of substance rate mole per second mol/s mol·s− 1.\nP power kilowatt kW 103·m2·kg·s− 3.\np pressure pascal Pa kg·m− 1·s− 2.\nρ mass density kilogram per cubic meter kg/m3 kg·m− 3.\nPL payload tons ton kg.\nφ direction degrees ° °.\nψ direction degrees ° °.\nr tire radius meter m m.\nr2 coefficient of determination\nRe # Reynolds number\nSEE standard error of the estimate\nσ standard deviation\nTRPM tire revolutions per mile revolutions per mile r/mi\nTRRL tire rolling resistance level newton per kilonewton N/kN 10− 3.\nT absolute temperature kelvin K K.\nT Celsius temperature degree Celsius °C K−273.15.\nT torque (moment of force) newton meter N·m m2·kg·s− 2.\nt time hour or second hr or s s.\nΔt time interval, period, 1/frequency second s s.\nUF utility factor\nv speed miles per hour or meters per second mi/hr or m/s m·s− 1.\nw weighting factor\nw wind speed miles per hour mi/hr m·s− 1.\nW work kilowatt-hour kW·hr 3.6·m2·kg·s− 1.\nwC carbon mass fraction gram per gram g/g 1.\nWR weight reduction pound mass lbm kg.\nx amount of substance mole fraction mole per mole mol/mol 1.\n(c) Superscripts. This part uses the following superscripts for modifying quantity symbols:\nTable 3 to § 1037.805—Superscripts\nSuperscript Meaning\noverbar (such as y ) arithmetic mean.\nDouble overbar (such as y) arithmetic mean of arithmetic mean.\noverdot (such as y ) quantity per unit time.\n(d) Subscripts. This part uses the following subscripts for modifying quantity symbols:\nTable 4 to Paragraph (d) of § 1037.805—Subscripts\nSubscript Meaning\n±6 ±6° yaw angle sweep.\nA A speed.\nair air.\naero aerodynamic.\nalt alternative.\nact actual or measured condition.\nair air.\naxle axle.\nB B speed.\nbrake brake.\nC C speed.\nCcombdry carbon from fuel per mole of dry exhaust.\nCD charge-depleting.\ncircuit circuit.\nCO2 DEF CO2 resulting from diesel exhaust fluid decomposition.\nCO2 PTO CO2 emissions for PTO cycle.\ncoastdown coastdown.\ncomp composite.\nCS charge-sustaining.\ncycle test cycle.\ndrive drive axle.\ndrive-idle idle with the transmission in drive.\ndriver driver.\ndyno dynamometer.\neffective effective.\nend end.\neng engine.\nevent event.\nfuel fuel.\nfull full.\ngrade grade.\nH2 Oexhaustdry H2 O in exhaust per mole of exhaust.\nhi high.\ni an individual of a series.\nidle idle.\nin inlet.\ninc increment.\nlo low.\nloss loss.\nmax maximum.\nmeas measured quantity.\nmed median.\nmin minimum.\nmoving moving.\nout outlet.\nP power.\npair pair of speed segments.\nparked-idle idle with the transmission in park.\npartial partial.\nploss power loss.\nplug-in plug-in hybrid electric vehicle.\npowertrain powertrain.\nPTO power take-off.\nrated rated speed.\nrecord record.\nref reference quantity.\nRL road load.\nrotating rotating.\nseg segment.\nspeed speed.\nspin axle spin loss.\nstart start.\nsteer steer axle.\nt tire.\ntest test.\nth theoretical.\ntotal total.\ntrac traction.\ntrac10 traction force at 10 mi/hr.\ntrailer trailer axle.\ntransient transient.\nTRR tire rolling resistance.\nUF utility factor.\nurea urea.\nveh vehicle.\nw wind.\nwa wind average.\nyaw yaw angle.\nys yaw sweep.\nzero zero quantity.\n(e) Other acronyms and abbreviations. This part uses the following additional abbreviations and acronyms:\nTable 5 to Paragraph (e) of § 1037.805—Other Acronyms and Abbreviations\nAcronym Meaning\nABT averaging, banking, and trading.\nAECD auxiliary emission control device.\nAES automatic engine shutdown.\nAPU auxiliary power unit.\nCD charge-depleting.\nCFD computational fluid dynamics.\nCFR Code of Federal Regulations.\nCITT curb idle transmission torque.\nCS charge-sustaining.\nDOT Department of Transportation.\nEPA Environmental Protection Agency.\nFEL Family Emission Limit.\nGAWR gross axle weight rating.\nGCWR gross combination weight rating.\nGEM greenhouse gas emission model.\nGVWR gross vehicle weight rating.\nHeavy HDE heavy heavy-duty engine (see 40 CFR 1036.140).\nHeavy HDV heavy heavy-duty vehicle (see § 1037.140).\nHVAC heating, ventilating, and air conditioning.\nISO International Organization for Standardization.\nLight HDE light heavy-duty engine (see 40 CFR 1036.140).\nLight HDV light heavy-duty vehicle (see § 1037.140).\nMedium HDE medium heavy-duty engine (see 40 CFR 1036.140).\nMedium HDV medium heavy-duty vehicle (see § 1037.140).\nNARA National Archives and Records Administration.\nNHTSA National Highway Transportation Safety Administration.\nPTO power take-off.\nRESS rechargeable energy storage system.\nSAE SAE International.\nSEE standard error of the estimate.\nSKU stock-keeping unit.\nSpark-ignition HDE spark-ignition heavy-duty engine (see 40 CFR 1036.140).\nTRPM tire revolutions per mile.\nTRRL tire rolling resistance level.\nU.S.C United States Code.\nVSL vehicle speed limiter.\n(f) Constants. This part uses the following constants:\nTable 6 to Paragraph (f) of § 1037.805—Constants\nSymbol Quantity Value\ng gravitational constant 9.80665 m·− 2.\nR specific gas constant 287.058 J/(kg·K).\n(g) Prefixes. This part uses the following prefixes to define a quantity:\nTable 7 to Paragraph (g) of § 1037.805—Prefixes\nSymbol Quantity Value\nµ micro 10− 6\nm milli 10− 3\nc centi 10− 2\nk kilo 103\nM mega 106","path":["Title 40—Protection of Environment","CHAPTER I—ENVIRONMENTAL PROTECTION AGENCY","SUBCHAPTER U—AIR POLLUTION CONTROLS","PART 1037—CONTROL OF EMISSIONS FROM NEW HEAVY-DUTY MOTOR VEHICLES","Subpart I—Definitions and Other Reference Information"],"source_url":"https://www.ecfr.gov/api/versioner/v1/full/2026-08-25/title-40.xml","current_through":"2026-08-25","vintage":"","retrieved_at":"2026-08-27T02:26:04Z","sha256":"a574f3e9036fd6218589fb09c86b7c8c9034a5683159f4d04131ec4871e8a259","source_id":"us-cfr","stale":true,"prev":"us/40-cfr-1037.801","next":"us/40-cfr-1037.810"},"notice":"GroundRules: Original legal text. Not legal advice."}