40 CFR § 1051.710 - How do I generate and bank emission credits?
(a) Banking is the retention of emission credits by the manufacturer generating the emission credits for use in averaging or trading in future model years. You may use banked emission credits only within the averaging set in which they were generated.
(b) If your average emission level is below the average standard, you may calculate credits according to § 1051.720. Credits you generate do not expire.
(c) You may generate credits if you are a certifying manufacturer.
(d) You may designate any emission credits you plan to bank in the reports you submit under § 1051.730. During the model year and before the due date for the final report, you may designate your reserved emission credits for averaging or trading.
(e) Reserved credits become actual emission credits when you submit your final report. However, we may revoke these emission credits if we are unable to verify them after reviewing your reports or auditing your records.