When you reach this point you must comply with Best Available Control Technology (BACT). BACT is defined as "Turnover" or "VDCECS". For definitions of both click on the "Turnover" or "VDECS" box in the compliance chart.
From the previous step you have identified your BACT obligation for a compliance date, which is calculated as:
For example, if you are a large fleet and have 5,600 hp on Jan 1, 2014 your hp BACT obligation would be: 5,600 X 4.8% or 269 hp. Assume you had 150 hp credit for early repowers. Your Jan 1, 2014 BACT obligation would be 119 hp. The regulation says if your obligation is more than one-half the hp of any machine in your fleet, then that machine is subject to BACT. For example, say the smallest hp machine in your off-road fleet on Jan 1, 2014 is 250 hp and you BACT obligation is 119 hp. In that case you would not have to take any compliance actions for that year. That is, 250 hp divided by two is 125 hp which is larger than your BACT obligation. So with a 119 hp BACT obligation you would be required to apply to BACT to any machine that is 238 hp or smaller.
It is also critical to remember that your obligation on a compliance date excludes your year-to-year low use equipment. This can be very tricky because your year-to-year low use exemption (less than 200 engine hours per year) covers the calendar year preceding a compliance deadline and ends on the date you are required to be compliant.
Consider another example. The year-to-year low use exemption applies to equipment used less than 200 hour per year. So considering the Jan 2014 deadline say you have five pieces of equipment that have run 150 hours between Jan 1, 2013 and Oct 1, 2013. You have a compliance deadline of Jan 1, 2014. So on Oct 1, 2013 you need to decide if those machines will in fact run less than 200 years during calendar year 2013. If you decide they will, then that will (1) reduce your BACT obligation on Jan 1, 2014 by 4.8% X five pieces of equipment X 200 hp or 48 hp, and (2) those five piece of equipment would be exempt from BACT for the Jan 1, 2014 compliance date. However, if you miss calculate and some of that equipment runs 200 or more hours during 2013 then you may or could have virtually no time to meet BACT by the Jan 1, 2014 deadline.
ARB has a calculator to help you identify your compliance status and BACT obligations. See:
Exemption from Turnover and VDECS Retrofits: Vehicles less than 10 years old are exempt from both turnover and VDECS retrofits.
Exemptions from Turnover: (1) A vehicle that was retrofit with PM VDECS that was either a Level 2 or Level 3, and that was highest efficiency available at the time of retrofit is exempt from turnover for six years. (2) Up to 15% of a fleets hp is exempt from turnover if retrofit with a Level 2 or Level 3, and that was highest efficiency available at the time of retrofit is permanently exempt from turnover.