Emission Calculations

This page last reviewed on November 19, 2008

This page contains instructions and emission calculators for Urban Bus and Transit Fleet Vehicle PM and NOx requirements. These calculators are provided for Transit Agencies' convenience to determine emission reductions`.

Particulate matter (PM) and oxides of nitrogen (NOx) calculations are based on the engine emission standards set forth in title 13, California Code of Regulations (CCR) section 1956.1 (urban bus engine standards) and 1956.8 (heavy-duty engine standards). Emission standards are listed below. Some engines may be certified to a lower optional standard for NOx. Typically, those are alternative-fuel engines. Check your engine's certification Executive Order or contact your dealer to get more information on your engine's emissions standard.

Particulate Matter Emission Standards

 

Urban Bus Engine

Heavy-Duty Diesel Engine

Engine Model Year

(g/bhp-hr)

(g/bhp-hr)

Pre-1988

1.0

1.0

1988-1990

0.6

0.6

1991-1993

0.1

0.25

1994-1995

0.07

0.1

1996-2002

0.05

0.1

2003-2006

0.01

0.1

2007+

0.01

0.01

NOx Emission Standards

 

Urban Bus Engine

Heavy-Duty Diesel Engine

Engine Model Year

(g/bhp-hr)

(g/bhp-hr)

Pre-1988

10.0

10.0

1988-1990

6.0

6.0

1991-1995

5.0

5.0

1996-1997

4.0

5.0

1998-2003

4.0

4.0

Oct. 2002-2003
(Settlement Agreement)

2.2(1)(2)

2.2(1)(2)

2004-2006 / Diesel

0.5

2.2(1)

2004-2006 / Alt-fuel

2.2(1)

2.2(1)

2007-2009

1.2(3)

1.2(3)

2010+

0.2

0.2


ARB has developed calculators to assist in determining your fleet's compliance. The calculators are set up to meet most fleets' needs, but if your engine criterion is not listed on the calculators, please contact ARB staff for assistance.

Download Urban Bus Calculator

Download Transit Fleet Vehicle Calculator


Using the calculator:

 Separate your fleet into urban buses and transit fleet vehicles.

First, identify your Urban Bus fleet (UB). If you have reported buses as UBs in the past, these buses remain in the UB category unless specific approval has been provided by Air Resources Board (ARB). Urban Buses that meet the definition of an "emergency contingency vehicle" defined in title 13, CCR section 2023(a)(4) are not included in the calculation.

Next, identify your Transit Fleet Vehicle fleet (TFV). Commuter Service Buses defined in title 13, CCR section 2023(a)(2) are included in yourTFV fleet. TFVs that meet the "low usage vehicle" criteria are not included in the calculation.

Most Urban Buses have engines certified to the urban bus emission standards. Most Transit Fleet Vehicles have engines certified to the heavy-duty engine standards. Always check your engine's certification prior to calculating your NOx or PM emissions.


TFV NOx average calculation.

Sum the number of diesel and alternative-fueled TFVs by model year grouping and enter the number into the appropriate cell. A reminder: many alternative-fueled engines are certified at a lower NOx value. For lower NOx engines, enter the engine model, the number of TFVs with that engine model and the "optional" emission standard for those engines in the appropriate cell at the bottom the calculator form.


UB and TFV PM reduction calculation.

Each fleet (UB vs TFV) is calculated separately. Sum the number of diesel TFVs or UBs by model year grouping and enter the number into the appropriate cell. The model year groupings are different for urban bus and heavy duty engines. Enter your baseline PM value.

Notes:

 

(1)

Nominal expected NOx level based on emission standards of 2.4 g/bhp-hr NOx plus non-methane hydrocarbons (NMHC) or 2.5 g/bhp-hr NOx plus NMHC with 0.5 g/bhp-hr NMHC cap to take effect in October 2002 for those engines subject to the Settlement Agreements between the heavy-duty engine manufacturers, the United States Environmental Protection Agency (U.S. EPA), and ARB. As part of the Settlement Agreements, the federal heavy-duty engine emission standards adopted for 2004 took effect in October 2002.

(2)

Seven engine manufacturers (Caterpillar, Cummins, Detroit Diesel, Mack, Navistar, Renault and Volvo) were required to "pull ahead" and meet the 2004 NOx emission standard by October 2002.

(3)

Between 2007 and 2009, U.S. EPA requires 50 percent of heavy duty diesel engine family certifications to meet the 0.2 g/bhp-hr NOx standard. Averaging is allowed, and it is expected that most engines will conform to the fleet NOx average of approximately 1.2 g/bhp-hr.

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