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Emission Standards

USA: Urban Bus Retrofit Rebuild (UBRR) Program


On April 21, 1993, EPA published final Retrofit/Rebuild Requirements for 1993 and Earlier Model Year Urban Buses (40 CFR Part 85 Subpart O). The retrofit/rebuild program is intended to reduce the ambient levels of particulate matter (PM) in urban areas and is limited to 1993 and earlier model year (MY) urban buses operating in metropolitan areas with 1980 populations of 750,000 or more, whose engines are rebuilt or replaced after January 1, 1995.

Compliance Programs

Operators of the affected buses are required to choose between two compliance programs:

  • Program 1 sets particulate matter emissions requirements for each urban bus engine in an operator's fleet which is rebuilt or replaced;
  • Program 2 is a fleet averaging program that sets out a specific annual target level for average PM emissions from urban buses in an operator's fleet.

A key aspect of the program is the certification of retrofit/rebuild equipment. To meet either of the two compliance options, operators of the affected buses must use equipment which has been certified by EPA. Emissions requirements under either of the two programs depend on the availability of retrofit/rebuild equipment certified for each engine model.

Program 1: To be used for Program 1, equipment must be certified as meeting the following PM requirements:

TierPM Requirement
125% reduction relative to the original engine certification
20.1 g/bhp-hr

If no certified equipment is available for a given engine model, the engine must be rebuild to its original PM emission certification level. Under Program 1, additional information regarding cost must be submitted in the application for certification, in order for certification of that equipment to initiate (or trigger) program requirements for a particular engine model. In order for the equipment to serve as a trigger, the certifier must guarantee that the equipment will be offered to affected operators for $7,940 or less at the 0.10 g/ bhp-hr PM level, or for $2,000 or less for the 25 percent or greater reduction in PM. Both of the above amounts are based on 1992 dollars and include life cycle costs incremental to the cost of a standard rebuild.

Program 2: Equipment used for Program 2 must be certified as providing some level of PM reduction that would in turn be claimed by urban bus operators when calculating their average fleet PM levels attained under the program.

Equipment certified under the UBRR program should meet emission performance durability, as well as mechanical durability requirements, which are warranted by certifier. The following warranties are required:

  • The certifier must warrant that the retrofit/rebuild equipment will not cause an urban bus engine to exceed emission requirements for a period of 150,000 miles from when the equipment is installed.
  • The certifier must replace all defective parts, free of charge for a period of 100,000 miles from when the equipment is installed.

There is no limitation on the time the warranties are in effect.

Certified Equipment