Appendix I 

School Bus Regulatory Requirement 

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School Bus Regulatory Requirements 

The reduction of diesel exhaust emissions is imperative to reducing all Californians 

exposure to cancer-causing and smog-forming compounds. School age children are an 

especially vulnerable segment of our population to the affects of air pollution. Reducing 

children’s exposure to the harmful affects of diesel exhaust can be achieved through the 

implementation of the proposed regulation. 

A. School Bus Regulatory Requirements 

Diesel-fueled school buses as defined in the California Vehicle Code section 545 with a 

GVWR above 14,000 pounds will need to install a Verified PM retrofit device meeting 

the requirements of the regulation. Unlike all the other vehicle sectors subject to the 

proposed NOx and PM requirements of the proposed regulation, school buses are only 

required to meet the proposed PM requirements and are subject to several special 

provisions and timetables specifically designed for this sector. School buses 

manufactured prior to April 1, 1977, before minimum federal safety standards, will be 

required to be removed from service by January 1, 2012. Proposition 1B, approved by 

California voters in 2006, will provide $200 million, through the Lower-Emission School 

Bus Program, to replace all remaining eligible pre-1977 model year school buses, 

replace approximately 1000 model year 1977 to 1986 school buses and install diesel 

particulate filters on about 3500 buses. All buses replaced or retrofitted through the 

Lower-Emission School Bus Program will be in compliance with the proposed 

regulation. All remaining diesel-fueled school buses must meet one of the following 

three proposed compliance options: 

• The Best Available Control Technology (BACT) Compliance Schedule 

• The BACT Percentage Limits Compliance option 

• Fleet Average Compliance Option 

School buses would be considered in compliance with the proposed regulation when 

they have installed the highest level VDECS available for the school buses engine, 

either a Level-2 or Level-3 (50 percent or 85 percent reduction in PM, respectively) by 

the designated compliance date under the option selected. Depending on the 

compliance option chosen and the VDECS that is installed, a school bus fleet may be 

subject to proposed reporting requirements. 

If it is not technologically feasible for the school bus engine to be retrofitted with a Level2 or Level-3 VDECS, then compliance may be delayed until January 1, 2018. Before 

the beginning of 2018 the unretrofittable school bus engine needs to be replaced with 

an engine that is in compliance with the proposed regulation or the school bus needs to 

be replaced. 
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B. The BACT Compliance Schedule Option 

It is anticipated most school bus fleets would use the BACT compliance option. School 

bus fleet operators would be required to retrofit specific model year school bus engines 

with the highest level VDECS meeting the requirements of the proposed regulation by 

specified dates as described in Table 1 below. School buses that can not be retrofitted 

with a Level-2 or higher VDECS will be allowed to delay compliance with the proposed 

regulation until January 1, 2018. However, operators will be required to report the 

status of that school bus engine to the ARB annually through 2017. 

 

Table 1: Best Available Control Technology Compliance Schedule for 

Schoolbus Fleets 

Compliance Deadline (as of January ) Engine Model-Years 

2011 2000 and newer 

2012 1994 – 1999 

2013 1987 – 1993 

2014 Pre-1987 

C. The BACT Percentage Limits Compliance Option 

School bus fleet operators that choose the BACT Percentage Limits compliance option 

will be required to retrofit a percentage of the school bus fleet with the highest level 

VDECS meeting the requirements of the proposed regulation by specified dates as 

described in Table 2 below. School buses that can not be retrofitted with a Level-2 or 

higher VDECS will be allowed to delay compliance with the proposed regulation until 

January 1, 2018. If the school bus fleet operator chooses the BACT Percentage Limits 

compliance option than all school buses in the fleet will need to be reported annually to 

the ARB. 

The percentage limits compliance option would work well for school bus fleets that 

either have a large number of newer school buses or school bus fleets that have taken 

advantage of available incentive funding to retrofit a large portion of their school bus 

fleet. School bus fleets that already have significant retrofit penetration into their fleet 

could potentially be in compliance with the proposed regulation for the first year or two. 

Table 2: Percent of Total School Bus Fleet That Must Comply with PM BACT 

Standard 

Compliance Deadline 

(as of January 1) 

Percent of Total Fleet Complying with PM 

BACT 

2011 25% 

2012 50% 

2013 75% 

2014 100% 
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D. Fleet Averaging Compliance Option 

School bus fleet operators that choose the fleet averaging compliance option will 

calculate the average emission level of their school bus fleet and compare that value 

with the fleet PM targets as indicated in the proposed regulation. The average emission 

level for the school bus fleet will need to be at or below the Fleet PM Targets provided 

in Section 2025 (h) of the proposed regulation to be considered in compliance. School 

bus fleets will reduce the emissions from their fleet by retrofitting school bus engines 

with the highest level VDECS and replacing older school buses with new buses meeting 

the 2007 diesel PM emission standard of 0.1 g PM/bhp-hr. School buses that can not 

be retrofitted with a Level-2 or higher VDECS will be allowed to delay compliance with 

the proposed regulation until January 1, 2018, however, these buses need to be 

included in the school bus fleet average calculation. School bus fleets that use 

alternative-fueled school buses will be allowed to use the credit for alternative-fueled 

vehicles. The credit for alternative-fueled vehicles can only be used with the Fleet 

Averaging Option. 

The fleet average compliance option is well suited for school bus fleets that are largely 

comprised of alternative-fueled vehicles with a small number of relatively newer diesel 

fueled school buses or school bus fleets that are largely comprised of new diesel-fueled 

school buses meeting the 0.01 g PM/bhp-hr emission level. 

E. Special Provisions for School Buses 

School buses are eligible for Low-Use Exemption if the school buses have a working 

odometer and travels less than 1000 miles per year, an hour meter will not be required 

to be installed. School buses that meet the requirements of the low-use exemption will 

be not be required to install a VDECS and can continue to be operated by the school 

bus fleet operator. Low-use school buses will not be required to be included in 

determining compliance with the regulation compliance options. School bus fleet 

operators that choose to use the low-use exemption are required to report that school 

bus to the ARB. 

School buses that are registered as historic vehicles and meet the requirements of 

historic vehicles as defined in the proposed regulation are exempt from the 

requirements of the proposed regulation. 

F. Available Incentive Funding for School Bus Fleet Operators 

Public school districts and public school districts operating as part of a joint powers 

authority are eligible for school bus replacement and retrofit funding under the LowerEmission School Bus Program. Private companies that contract with public school 

districts are eligible for retrofit funding under the Lower-Emission School Bus Program. 

Typically the local air district implements the Lower-Emission School Bus Program in 

their area. However, some smaller and medium sized air districts have chosen to have 

the ARB implement the Program in their air districts. School districts that are interested 

in he Lower-Emission School Bus Program should contact their local air district to 

determine who is implementing the Program in their area. 
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Assembly Bill 923 (AB 923, Stat 2004 Ch 707) is another possible source of funding for 

school bus replacement funding. This legislation has provided a mechanism for air 

district to increase the motor vehicle registration fee surcharge from four dollars to six 

dollars. The additional two dollar surcharge may be used by the air district for four 

different clean air categories, including school bus replacement projects pursuant to 

California’s Lower-Emission School Bus Program. Not all air districts are allowed to 

collect the DMV registration fee and some air districts choose not to assess the fee. 

Public school districts should contact their local air districts to see if AB 923 funds are 

available for school bus replacement. The California Department of Education’s Small 

School District School Bus Replacement Program provides funding for the replacement 

of older school bus for public school districts with an average daily attendance below 

2,501 students, school districts should contact the California Department of Education 

for information on this program. 

Private schools are not eligible for school bus replacement or retrofit funds from the 

Lower-Emission School Bus Program. A more in depth discussion on incentive funding 

for school bus replacement and retrofit funding can be found in Chapter XV of the staff 

report. 

G. Existing School Bus Fleet 

Currently there are about 24,000 school buses that transport children to and from 

school in California. Although alternative-fueled school buses have become very 

common in California over the last decade, the in-use school bus fleet operating in 

California is still primarily diesel-fueled. School buses tend to accrue fewer miles than 

other heavy-duty vehicles operating in California, which leads to vehicles having a long 

useful life. As such, school bus fleets tend to be comprised of buses that have been or 

will operate for 30 years or more. 

The oldest school buses still in operation in school bus fleets are from the 1973 model 

year. With the financial assistance provided through California’s Lower-Emission 

School Bus Program the remaining pre-1977 model year school buses will be replaced 

by February 2010, as well as about 40 percent of the remaining pre-1987 model year 

school buses by the middle of 2011. 

In addition, approximately 10 percent of the school bus fleet still uses 2-stroke diesel 

engines, many of which have uncontrolled diesel PM emissions. These buses can not 

be retrofitted, therefore it is expected that these 2-stroke engine school buses will need 

to be replaced by the end of 2017 to comply with the proposed regulation. 

Currently, approximately 20 percent of the in-use school bus fleet has already been 

retrofitted with a diesel particulate filter putting them in compliance with the proposed 

regulation. A further 10 percent of the school bus fleet has a diesel particulate filter 

installed by the engine manufacturer and are therefore in compliance with the proposed 

regulation, as well as all model year alternative-fueled school buses Overall, at least 

one-third of the fleet meets the proposed requirements today. 
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H. Existing Technology Availability for School Buses 

School buses were one of the first vehicle classes to be retrofitted with diesel particulate 

filters and as such some school bus fleet operators have become very experienced with 

VDECS. Not all diesel engines are suitable for VDCES retrofit. Some engines, like 2-

stroke engines do not have a VDECS available meeting the requirements of the 

proposed regulation. 

School bus fleets have been able to employ both active and passive style diesel 

particulate filters on school bus engines. Active style diesel particulate filters require an 

external heat source to oxidize the collected diesel PM while passive style filters use the 

heat from the engine with the help of a catalyzed filter washcoat to force the oxidization 

of the collected diesel PM while the school bus is in operation. Typically, newer buses 

employ less expensive passive style filters while older school bus engines require the 

use of active style filters. 

Generally, school bus engines manufactured before 1987 can not be retrofitted with 

either a passive or active diesel particulate filter. School bus engines from model year 

1987 to 1993 can typically be retrofitted with active filters with the exception of the 2-

stroke engines. School bus engines from model year 1994 to 2002 are good 

candidates for retrofit with most of these engines being able to be retrofitted with the 

passive-style filter. School bus engines from model year 2003 to 2006 generally employ 

exhaust gas recirculation systems to reduce the levels of NOx in the exhaust. Currently 

there are not any PM filters verified for 2003 to 2006 model year engines, but it is 

anticipated that PM filters will be verified in the near future. 

If an engine in a school bus is not retrofittable, the engine can potentially be replaced 

with an engine that can be retrofitted. Repowering a school bus with a newer engine 

may be feasible for some school bus fleet operators that wish to maintain their older 

school buses in operation. 

Since 2001 all school buses funded under California’s Lower-Emission School Bus 

Program had diesel particulate filters installed and are in compliance with the proposed 

regulation. Diesel engines manufactured for model year 2007 and newer have diesel 

particulate filters installed by the engine manufacturer and are considered in compliance 

with the proposed regulation. 
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