OVERVIEW OF THE 2000, 2002, 2004, AND 2005 

TRANSIT AGENCY AND URBAN BUS RULEMAKINGS 

A. The 2000 Rulemaking 

The hearings in the first rulemaking were conducted on January 27 and February 24, 

2000, following issuance of the public hearing notice on December 10, 1999. At the 

February 24, 2000, hearing, the Board adopted Resolution 00-2, in which it approved 

the adoption of sections 1956.1, 1956.2, 1956.3, and 1956.4 in the California Code of 

Regulations, title 13, relating to emission standards for urban buses and fleet 

requirements for transit agencies using urban buses.1

 The Board also approved 

amendments to the “California Exhaust Emission Standards and Test Procedures for 

1985 and Subsequent Model Heavy-Duty Diesel Engines and Vehicles,” incorporated 

by sections 1956.1(b) and 1956.8(b), and amendments to the “California Motor Vehicle 

Emission Control and Smog Index Label Specifications” (Label Specifications), 

incorporated by reference in section 1965.2

 After complying with the administrative 

rulemaking procedures set forth in California law, the Executive Officer finalized the 

Board action and adopted the amendments and the new provisions on 

November 22, 2000, and May 29, 2001, by issuing Executive Orders G-00-060 

and G-01-010, respectively. 

The 2000 rulemaking consisted primarily of two complementary elements designed to 

reduce emissions from urban buses: (a) a multi-component urban bus fleet rule 

applicable to public transit agencies and (b) more stringent emission standards for 

urban bus engines applicable to urban bus engine manufacturers. 

The Board’s 2000 amendments to the urban bus emission standards made them 

increasingly more stringent in multiple stages depending on fuel type. First, the Board 

established a more stringent particulate matter (PM) emission standard of 0.01 grams 

per brake horsepower-hour (g/bhp-hr) for 2002 and later model-year diesel-fuel, 

dual-fuel, and bi-fuel urban bus engines produced on or after October 1, 2002, 

representing an 80-percent reduction from the preexisting PM standard. Second, for 

the 2004 through 2006 model years (MY), the amendments increased the stringency of 

the oxides of nitrogen (NOx), nonmethane hydrocarbon (NMHC), carbon monoxide 

(CO), and formaldehyde standards for all urban bus engines and provided optional 

 

1

 All section citations are to the California Code of Regulations, title 13, unless otherwise specified. 

Section numbers 1956.1-1956.4 were available to codify the new regulations because obsolete provisions 

earlier codified under those section numbers had been repealed by a previous rulemaking. In a later 

rulemaking in 2007, sections 1956.2, 1956.3, and 1956.4 were reorganized and renumbered in section 

2023 and sections 2023.1-2023.4. In the 2000 rulemaking, section 1956.8, which had codified CARB’s 

urban bus standards along with other heavy-duty engine and vehicle standards, was amended to 

bifurcate the urban bus standards from the other heavy-duty standards and to amended the incorporated 

standards and test procedures. 

2

 In addition, the Board approved adoption of the “California Certification Procedures for PM Retrofit 

Devices for On-Road Heavy-Duty Diesel Engines,” incorporated by reference in section 1956.2(f)(7). This 

document was repealed in the 2004 Urban Bus rulemaking and was in any event not preempted by CAA 

section 209(a) because it pertained solely to retrofits for “non-new” engines. It accordingly is not covered 

by CARB’s waiver request.

1
standards as well. For urban bus engines other than diesel-fuel, dual-fuel, and bi-fuel 

engines, the emissions standards for 2004 through 2006 were set at 2.4 g/bhp-hr for 

NOx plus NMHC (NOx + NMHC), 15.5 g/bhp-hr for CO, and 0.05 g/bhp-hr for PM 

(0.07g/bhp-hr PM in-use).3 For diesel-fueled, dual-fuel, and bi-fuel urban bus engines 

in the 2004-2006 model years, the standards were set at 0.5 g/bhp-hr NOx, 

representing a 75 percent reduction in the preexisting NOx standard; 0.01 g/bhp-hr PM

(maintaining the October 2002 standards), 0.05 g/bhp-hr NMHC, 5.0 g/bhp-hr CO, and 

0.01 g/bhp-hr formaldehyde. Third, beginning with the 2007 model year, all urban

engines (regardless of fuel type) had to meet more stringent emission standards for

NOx at 0.2 g/bhp-hr, NMHC at 0.05 g/bhp-hr, CO at 5.0 g/bhp-hr, and formaldeh

0.01 g/bhp-hr. 

 bus 

yde at 

 

As originally established in the 2000 rulemaking, the fleet rule for public transit agencies 

operating urban buses featured several components, including (a) requiring the public 

transit agency to select one of two compliance paths – either the “alternative-fuel path” 

or the “diesel path”; (b) an in-use NOx fleet average requirement of 4.8 g/bhp-hr 

applicable October 1, 2002, for public transit agencies; (c) requirements that public 

transit agencies retrofit progressively newer model-year in-use diesel-fuel, dual-fuel, 

bi-fuel and diesel fuel hybrid-electric urban buses with devices capable of reducing PM 

emissions by 85 percent, and (d) requirements that large public transit agencies on the 

diesel path establish zero-emission bus demonstration projects beginning in July 2003, 

and that all large public transit agencies make at least 15 percent of their new urban bus 

purchases qualify as zero-emission buses starting in 2008-2010.4

B. The 2002 Amendments 

The second regulatory action occurred in 2002. In recognition of the progressive nature 

of the fleet rule and emission standards, CARB staff worked with public transit agencies, 

urban transit bus manufacturers, and engine and drive system manufacturers to gather 

and evaluate implementation information. In response to direction from the Board 

during public meetings conducted in September 2001 and March 2002, CARB staff 

proposed amendments to the public transit agency fleet rule, deleting previously 

3

 These standards were set for urban buses in a 1998 CARB rulemaking for heavy heavy-duty diesel 

engines which established standards for the 2004 and later model years. Urban buses were included in 

the waiver determination request CARB submitted to the Administrator on December 26, 2001. 

4

 Section 1956.3(b) required a demonstration project for zero-emission buses for which public transit 

agencies were to prepare and solicit bids. The demonstration-project requirement is within the 

market-participant doctrine as it is an exercise of the state’s proprietary function with respect to transit 

agency purchases and is accordingly not covered by the instant waiver request. See footnote 1. The 

15-percent zero-emission bus purchase requirement for large public transit agencies (§ 1956.3(c)) was 

initially set to be implemented in MY 2008, but delayed to MY 2011 in a subsequent rulemaking in 2006. 

CARB will further delay the 15-percent purchase requirement in a rulemaking anticipated in the last 

quarter of 2010 (see Enclosure 39). The need for a waiver, if any, for the 15-percent purchase 

requirement will be addressed with the future rulemaking. Section 1956.2(f)(5) prohibited, beginning 

July 1, 2002, most transit agencies from operating diesel buses on diesel fuel with a sulfur content 

exceeding 15 parts per million. Under CAA section 211(c)(4)(B), California is not preempted from 

administering this requirement, and the diesel fuel sulfur content requirement accordingly is not covered 

by the instant waiver request. 

2
adopted requirements requiring the use of PM retrofit devices, and adopted a new 

heavy-duty hybrid electric vehicle interim certification procedure. 

Following issuance of the public hearing notice on September 6, 2002, the Board 

approved the 2002 amendments and the new interim certification procedure at an 

October 24, 2002, hearing by adoption of Resolution 02-30. After complying with the 

administrative rulemaking procedures, the Executive Officer on September 2, 2003, 

issued Executive Order G-03-023, in which she formally adopted the amendments to 

sections 1956.1, 1956.2, 1956.4, 1956.8, and 2112 and adopted the “California Interim 

Certification Procedures for 2004 and Subsequent Model Hybrid-Electric Vehicles, in 

the Urban Bus and Heavy-Duty Vehicle Classes,” incorporated by reference in section 

1956.1(c) and 1956.8(b). The amendments were filed with OAL on September 4, 2003, 

and approved by OAL on October 16, 2003. 

Most of the 2002 amendments pertained to the fleet rule for public transit agencies, 

including the following: (a) replacing the PM emissions retrofit requirements with 

provisions requiring a public transit agency to reduce its overall diesel fleet PM 

emissions by percentages that increase in four steps from 2004 to 2009; (b) allowing a 

public transit agency in the SCAQMD to change its fuel path selection from diesel to 

alternative fuel on a one-time basis by January 31, 2004; (c) eliminating a restriction 

that prohibited a public transit agency on the diesel path from purchasing model-year 

2004-2006 alternative-fuel urban bus engines with NOx emissions in excess of 0.5 

g/bhp-hr, and (d) authorizing the Executive Officer to delay implementation for a small 

public transit agency based on financial hardship. Of import to the emission standards, 

as noted above, CARB adopted heavy-duty hybrid-electric vehicle interim certification 

procedures. It also allowed the use of a small quantity of diesel as a pilot ignition 

source in alternate-fueled engines, which previously had been precluded.5

 

C. The 2004 Amendments 

The third set of amendments, adopted by the Board in Resolution 04-19 at its 

June 24, 2004, public hearing, made further adjustments to the fleet rule in response to 

the state of bus engine technology. These amendments relaxed the NOx exhaust 

emission standard for model years 2004-2006 from 0.5 g/bhp-hr to 1.8 g/bhp-hr for 

diesel fuel hybrid-electric buses sold to a transit agency on the diesel path that has 

demonstrated to the Executive Officer that the agency will undertake measures that 

mitigate the excess NOx emissions. The amendments also adjusted the zero-emission 

bus demonstration requirements for public transit agencies in light of the high cost and 

late availability of fuel cells for urban bus applications. The regulatory sections 

amended were sections 1956.1, 1956.2, 1956.3, and 1956.4. On January 7, 2005, the 

amendments were submitted to OAL, which approved them on January 31, 2005. 

 

5

 These engines are referred to as heavy-duty pilot ignition engines. 

3
D. The February 2005 Amendments 

The fourth set of amendments, adopted by the Board in Resolution 05-15 at its 

February 24, 2005, public hearing, largely established additional or modified fleet 

requirements for public transit agencies. Most significantly, the rulemaking established 

requirements for public transit agencies operating vehicles defined as transit fleet 

vehicles. Under these provisions, public transit agencies must meet additional fleet 

requirements for on-road vehicles in their fleet, other than urban buses, that have a 

gross vehicle weight rating (GVWR) of greater than 8,500 pounds that are powered by 

heavy-duty diesel fueled or diesel-cycle alternative fueled engines, including vehicles 

defined as commuter service buses. The fleet regulations established increasingly 

more stringent fleet average NOx and PM emission requirements to be phased in 

between 2007 and 2010. In establishing the fleet average requirements, the Board 

relied on emission reductions that would be achieved from use of new engines used in 

new transit fleet vehicles or in repowering existing transit fleet vehicles with engines that 

meet previously adopted cleaner heavy-duty diesel engine emission standards and on 

the use of retrofit devices that reduce emissions of older engines used in transit fleet 

vehicles.6

The other amendments to the public transit agency fleet rules included (a) an added 

option for transit agencies to meet the urban bus PM fleet average requirement in a way 

that would allow for fleet growth; (b) guidance for newly formed public transit agencies 

formed after the adoption of the fleet rules for public transit agencies; and (c) recodifying 

the public transit agency fleet requirements in sections 1956.2-1956.4 to section 2023 et 

seq. so that they are included within Article 4 and CARB’s other in-use on-road fleet 

rules. 

The February 2005 amendments also corrected the 2004-2006 model-year emission 

standards for diesel hybrid-electric engines used in urban buses. When the standards 

were amended in the 2004 rulemaking, they inadvertently omitted the then existing 

standards for NMHC and carbon monoxide (CO). The 2005 amendments reinserted the 

engine exhaust emission standards of 0.5 g/bhp-hr for NMHC and 15.5 g/bhp-hr for CO; 

the amendments also removed the formaldehyde standard. The new and amended 

regulations were submitted to OAL on December 19, 2005, and were approved on 

January 31, 2006. 

E. The September and October 2005 Amendments 

The final set of amendments covered by this request was considered by the Board 

during three public hearings − September 15, 2005, October 20, 2005, and 

October 27, 2005. At the September 15 public hearing, the Board approved in 

Resolution 05-47 amendments to section 2023.1 that require all public transit agencies 

in the South Coast Air Quality Management District (SCAQMD) to follow the alternative-

 

6

 Under CAA section 209(a), retrofit requirements are not preempted because they are required on used 

engines and vehicles and are therefore not part of this waiver determination request. 

4
5

 

fuel path in complying with the Fleet Rule for Transit Agencies − Urban Bus 

Requirements. 

At the October 20 and 27 hearings, the Board considered amendments to the urban bus 

exhaust emission standards and to the fleet rule for public transit agencies statewide. 

At the conclusion of the October 20 hearing, the Board adopted Resolution 05-53, in 

which it approved amendments to the urban bus exhaust emission standards to align 

them with California’s existing exhaust emission standards for heavy-duty diesel-cycle 

engines7

 and deferred final approval of amendments to the Fleet Rule for Transit 

Agencies − Urban Bus Requirements to October 27, when CARB staff reported on the 

likely effect that the fleet requirements would have on public transit agencies. At the 

October 27 hearing, the Board adopted Resolution 05-61, which approved and required 

diesel path public transit agencies with more than 30 urban buses in their fleets to 

retrofit additional diesel fleet urban buses and other public transit agency vehicles if they 

purchase 2007 through 2009 diesel fuel urban buses whose engines were not certified 

at or below 0.2 g/bhp-hr for NOx. After complying with California rulemaking law, the 

Executive Officer finalized the Board action and adopted the amendments on 

July 28, 2006, by issuing Executive Order R-050-07. The Office of Administrative Law 

approved the regulations for filing and filed them with the Secretary of State on 

September 7, 2006. 

7

 See the United States Environmental Protection Agency (EPA) notice of its decision to grant a waiver of 

preemption for these standards in 70 Fed.Reg. 50322 (Aug. 26, 2005).