This summary covers the historical US EPA Tier 1 standards that are no longer in effect—they have been replaced by Tier 2 emission regulations.

Introduction

Two sets of standards have been defined for light-duty vehicles in the Clean Air Act Amendments (CAAA) of 1990:

  • Tier 1 standards, which were published as a final rule on June 5, 1991 and phased-in progressively between 1994 and 1997.
  • Tier 2 standards, which were adopted on December 21, 1999, with a phase-in implementation schedule from 2004 to 2009.

Tier 1 standards applied to all new light-duty vehicles (LDV), such as passenger cars, light-duty trucks, sport utility vehicles (SUV), minivans and pick-up trucks. The LDV category included all vehicles of less than 8500 lb gross vehicle weight rating, GVWR (vehicle weight plus rated cargo capacity). LDVs were further divided into the following sub-categories:

  • Passenger cars
  • Light light-duty trucks (LLDT), below 6000 lbs GVWR
  • Heavy light-duty trucks (HLDT), above 6000 lbs GVWR

FTP Emission Standards

The Tier 1 emission standards are summarized in Table 1. Car and light truck emissions were measured over the Federal Test Procedure (FTP 75) and expressed in g/mile. Separate sets of standards were defined for each vehicle category, with more relaxed limits for heavier vehicles.

Table 1
EPA Tier 1 Emission Standards for Passenger Cars and Light-Duty Trucks, FTP 75, g/mi
Category50,000 miles/5 years100,000 miles/10 years1
THCNMHCCONOx†
diesel
NOx
gasoline
PM‡THCNMHCCONOx†
diesel
NOx
gasoline
PM‡
Passenger cars0.410.253.41.00.40.08-0.314.21.250.60.10
LLDT, LVW <3,750 lbs-0.253.41.00.40.080.800.314.21.250.60.10
LLDT, LVW >3,750 lbs-0.324.4-0.70.080.800.405.50.970.970.10
HLDT, ALVW <5,750 lbs0.32-4.4-0.7-0.800.466.40.980.980.10
HLDT, ALVW > 5,750 lbs0.39-5.0-1.1-0.800.567.31.531.530.12
1 - Useful life 120,000 miles/11 years for all HLDT standards and for THC standards for LDT
† - More relaxed NOx limits for diesels applicable to vehicles through 2003 model year
‡ - PM standards applicable to diesel vehicles only

Abbreviations:
LVW - loaded vehicle weight (curb weight + 300 lbs)
ALVW - adjusted LVW (the numerical average of the curb weight and the GVWR)
LLDT - light light-duty truck (below 6,000 lbs GVWR)
HLDT - heavy light-duty truck (above 6,000 lbs GVWR)

SFTP Emission Standards

In addition to the FTP 75 test, a Supplemental Federal Test Procedure (SFTP) was phased-in between 2000 and 2004. The SFTP includes additional test cycles to measure emissions during aggressive highway driving (US06) and to measure urban driving emissions while the vehicle’s air conditioning system is operating (SC03).

The Tier 1 SFTP standards, which applied to NMHC+NOx and CO emissions, are summarized in Table 2. The NMHC+NOx standards were weighted, while CO standards were standalone for US06 and SC03, with an option for a weighted standard. Weighting for NMHC+NOx and optional weighting for CO was SFTP = 0.35 × FTP + 0.28 × US06 + 0.37 × SC03. Intermediate life (50,000 mi) standards are shown in parentheses.

Table 2
EPA Tier 1 SFTP Standards
Category*NMHC+NOx, g/miCO, g/mi
WeightedUS06SC03Weighted
Passenger cars & LLDT, LVW <3,750 lbs0.91/2.07† (0.65/1.48†)11.1 (9.0)3.7 (3.0)4.2 (3.4)
LLDT, LVW >3,750 lbs1.37 (1.02)14.6 (11.6)4.9 (3.9)5.5 (4.4)
HLDT, ALVW <5,750 lbs1.44 (1.02)16.9 (11.6)5.6 (3.9)6.4 (4.4)
HLDT, ALVW >5,750 lbs2.09 (1.49)19.3 (13.2)6.4 (4.4)7.3 (5.0)
* See note to Table 1 for abbreviations
† The more relaxed value is for diesel fueled vehicles

National LEV Program

On December 16, 1997, EPA finalized the National Low Emission Vehicle (NLEV) program [63 FR 926, 7 Jan 1998]. The NLEV was a voluntary program that came into effect through an agreement by the northeastern states and the auto manufacturers. It provided more stringent emission standards for the transitional period before the introduction of Tier 2 regulations. Starting in the northeastern states in model year 1999 and nationally in model year 2001, new cars and light light-duty trucks had to meet tailpipe standards that were more stringent than EPA could legally mandate prior to model year 2004. However, after the NLEV program was agreed upon, these standards were enforceable in the same manner as any other federal new motor vehicle program.

The National LEV program harmonized the federal and California motor vehicle standards and provided emission reductions that were basically equivalent to the California Low Emission Vehicle program. The program was phased-in through schedules that required car manufacturers to certify a percentage of their vehicle fleets to increasingly cleaner standards (TLEV, LEV, ULEV). The National LEV program extended only to lighter vehicles and did not include the Heavy LDT (HLDT, GVWR>6,000 lbs) vehicle category.