(2) Terms used in the equations in this paragraph (a) are defined as follows:

(2) Terms used in the equations in this paragraph (a) are defined as follows:

(b) Highway fuel economy.

(1) For each vehicle tested under § 600.010-08(a), (b), or (c), as applicable, determine the 5-cycle highway fuel economy using the following equation:

(2) If the condition specified in § 600.115-08(b)(2)(iii)(B) is met, in lieu of using the calculation in paragraph (b)(1) of this section, the manufacturer may optionally determine the highway fuel economy using the following modified 5-cycle equation which utilizes data from FTP, HFET, and US06 tests, and applies mathematic adjustments for Cold FTP and SC03 conditions:

(i) Perform a US06 test in addition to the FTP and HFET tests.

(ii) Determine the 5-cycle highway fuel economy according to the following formula:

(3) Terms used in the equations in this paragraph (b) are defined as follows:

(c) Fuel economy calculations for hybrid electric vehicles. Test hybrid electric vehicles as described in SAE J1711 (incorporated by reference in § 600.011). For FTP testing, this generally involves emission sampling over four phases (bags) of the UDDS (cold-start, transient, warm-start, transient); however, these four phases may be combined into two phases (phases 1 + 2 and phases 3 + 4). Calculations for these sampling methods follow:

(1) Four-bag FTP equations. If the 4-bag sampling method is used, manufacturers may use the equations in paragraphs (a) and (b) of this section to determine city and highway fuel economy estimates. If this method is chosen, it must be used to determine both city and highway fuel economy. Optionally, the following calculations may be used, provided that they are used to determine both city and highway fuel economy:

(i) City fuel economy.

(ii) Highway fuel economy.

(2) Two-bag FTP equations. If the 2-bag sampling method is used for the 75 °F FTP test, it must be used to determine both city and highway fuel economy. The following calculations must be used to determine both city and highway fuel economy:

(i) City fuel economy.

(ii) Highway fuel economy.

(3) For hybrid electric vehicles using the modified 5-cycle highway calculation in paragraph (b)(2) of this section, the equation in paragraph (b)(2)(ii)(A) of this section applies except that the equation for Start Fuel75 will be replaced with one of the following:

(i) The equation for Start Fuel75 for hybrids tested according to the 4-bag FTP is:

(ii) The equation for Start Fuel75 for hybrids tested according to the 2-bag FTP is:

(4) Terms used in the equations in this paragraph (b) are defined as follows:

(d) City CO2emissions and carbon-related exhaust emissions. For each vehicle tested, determine the 5-cycle city CO2 emissions and carbon-related exhaust emissions using the following equation:

(2) To determine the City CO2 emissions, use the appropriate CO2 grams/mile values instead of CREE values in the equations in this paragraph (d).

(3) Terms used in the equations in this paragraph (d) are defined as follows:

(e) Highway CO2emissions and carbon-related exhaust emissions.

(1) For each vehicle tested, determine the 5-cycle highway carbon-related exhaust emissions using the following equation:

(2) If the condition specified in § 600.115-08(b)(2)(iii)(B) is met, in lieu of using the calculation in paragraph (e)(1) of this section, the manufacturer may optionally determine the highway carbon-related exhaust emissions using the following modified 5-cycle equation which utilizes data from FTP, HFET, and US06 tests, and applies mathematic adjustments for Cold FTP and SC03 conditions:

(i) Perform a US06 test in addition to the FTP and HFET tests.

(ii) Determine the 5-cycle highway carbon-related exhaust emissions according to the following formula:

(3) To determine the Highway CO2 emissions, use the appropriate CO2 grams/mile values instead of CREE values in the equations in this paragraph (e).

(4) Terms used in the equations in this paragraph (e) are defined as follows:

(f) CO2and carbon-related exhaust emissions calculations for hybrid electric vehicles. Test hybrid electric vehicles as described in SAE J1711 (incorporated by reference in § 600.011). For FTP testing, this generally involves emission sampling over four phases (bags) of the UDDS (cold-start, transient, warm-start, transient); however, these four phases may be combined into two phases (phases 1 + 2 and phases 3 + 4). Calculations for these sampling methods follow:

(1) Four-bag FTP equations. If the 4-bag sampling method is used, manufacturers may use the equations in paragraphs (a) and (b) of this section to determine city and highway CO2 and carbon-related exhaust emissions values. If this method is chosen, it must be used to determine both city and highway CO2 emissions and carbon-related exhaust emissions. Optionally, the following calculations may be used, provided that they are used to determine both city and highway CO2 and carbon-related exhaust emissions values:

(i) City CO2emissions and carbon-related exhaust emissions.

(ii) Highway CO2emissions and carbon-related exhaust emissions.

(2) Two-bag FTP equations. If the 2-bag sampling method is used for the 75 °F FTP test, it must be used to determine both city and highway CO2 emissions and carbon-related exhaust emissions. The following calculations must be used to determine both city and highway CO2 emissions and carbon-related exhaust emissions:

(i) City CO2emissions and carbon-related exhaust emissions.

(ii) Highway CO2emissions and carbon-related exhaust emissions.

(3) For hybrid electric vehicles using the modified 5-cycle highway calculation in paragraph (e)(2) of this section, the equation in paragraph (e)(2)(ii)(A) of this section applies except that the equation for Start CREE75 will be replaced with one of the following:

(i) The equation for Start CREE75 for hybrids tested according to the 4-bag FTP is:

(ii) The equation for Start CREE75 for hybrids tested according to the 2-bag FTP is:

(4) To determine the City and Highway CO2 emissions, use the appropriate CO2 grams/mile values instead of CREE values in the equations in paragraphs (f)(1) through (3) of this section.

(5) Terms used in the equations in this paragraph (e) are defined as follows: