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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY

2000 TRAVERWOOD DRIVE

ANN ARBOR, MI 48105-2498

 OFFICE OF

AIR AND RADIATION

February 12, 2016

MEMORANDUM

SUBJECT: Vocational Vehicle Technology Packages for Custom Chassis

FROM: Lauren Steele, Environmental Engineer, OTAQ/ASD

TO: Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Mediumand Heavy-Duty Engines and Vehicles - Phase 2 - Docket EPA-HQ-OAR-2014-

0827

Introduction

This memorandum describes technology packages developed for select vocational 

vehicles manufactured as custom chassis. The agencies requested comment on whether to 

develop separate standards for these, though we did not propose to do so. The agencies received 

comments indicating that, for manufacturers unable to use emission averaging, the primary 

vocational vehicle standards were not feasible for some types of vehicles, thus in response, a 

specific technical feasibility analysis has been conducted for vehicles in seven vocations. 

Definitions

While we did not propose a definition of what would qualify as a custom vocational 

vehicle, we requested comment on this. Based on the information available, we believe that a 

reasonable definition could be a vehicle whose final intended build can be attested by the chassis 

manufacturer to be one of the seven vehicle types listed in Table 1. If a chassis may be finished 

into one of the vehicle types listed, but the certifying manufacturer is unable to know this, or 

unable to establish controls to ensure this at the time of certification, then it would not be a 

custom vocational vehicle.

The selection of specific vocations for this analysis has been informed by business 

information about chassis manufacturers who have certified to the Phase 1 standards, public 

comments, and other stakeholder outreach. The agencies have listed in Table 1 some attributes 

that may be used to distinguish custom chassis from other vocational vehicles. Conversations 

are ongoing regarding identifiable attributes of small transit and shuttle buses in weight classes 

2b-5. We are also considering aligning our defined attributes with those of NHTSA, which has 
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recently adopted a rule requiring seat belts on “over-the-road” buses,1 meaning those 

characterized by an elevated passenger deck located over a baggage compartment, as well as 

buses having a GVWR of 11,793 kg (26,000 lb) or greater, except school buses, urban transit 

buses, and some others.

Table 1: Custom Chassis Types

Vehicle Type Potentially Distinguishable Features

Coach (Intercity) 

Bus

Front doors only, no standing passengers, high-backed seats, possibly 

restroom facilities, luggage compartment, no onboard fare-collection 

Transit Bus Both front and center doors, low-back seating, passenger stop-request 

system, possibly rear engine, low floors, standing passenger positions, 

wheelchair lifts, onboard fare-collection

Motor Home 

(recreational 

vehicle)

Primary purpose is temporary housing; both propulsion engine and 

sleeping quarters

School Bus Primary purpose is pupil transport

Refuse Truck Low cab forward, primary purpose is collection of solid waste

Cement Mixer Primary purpose is delivery of freshly mixed concrete

Emergency Vehicle Fire truck or ambulance, defined at 40 CFR 86.1803

Industry Characterization

Based on public comments, information on entities who have certified, and stakeholder 

outreach, we have compiled an illustration of the level of diversification of the vocational vehicle 

manufacturers supplying these seven vocations in Table 2. This table is not intended to be 

exhaustive, rather illustrate that there are several manufacturers who are not diversified in their 

products, who are competing for sales with diversified manufacturers. Based on the definition 

above, it would be likely that the single-type (non-diversified) manufacturers would be able to 

certify their products as custom vocational vehicles, while only some of the multiple-type 

manufacturers (diversified) would have sufficient knowledge about, or control over, the intended 

use of their products to certify one or more types as custom vocational vehicles.

Table 2: Diversification of Vocational Chassis Manufacturersa

Vehicle Type Number of Single-type 

Chassis Manufacturers

Number of Multiple-type 

Chassis Manufacturers

Coach (Intercity) Bus 2 3

Motor Home 3 8

School Bus 1 2

Transit Bus 4 4

Refuse Truck 1 6

Cement Mixer 2 7

Emergency Vehicle 6 7

a

Includes U.S.-made vehicles and those imported for sale in the U.S.

 

1 See Occupant Crash Protection rule, November 25, 2013, 78 FR 70415, 49 CFR 571, FMVSS 208
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Structure of Phase 2 Program

Based on public comment and stakeholder outreach, the following approach has been 

developed. For any model year of the Phase 2 program, a manufacturer of one or more 

vocational chassis certified as custom vocational vehicles would be expected to meet the 

alternate standards set specifically for the identified vehicle type, using a simplified GEM

interface, where the engine and driveline-specific GEM inputs would be set as EPA defaults, as 

described in the proposal for emergency vehicles. Election of this option could include the 

flexibility to comply on average within a weight class across a manufacturer’s custom production 

in that year, and it could include the flexibility to bank credits for future years. However, it 

would not provide for trading of credits with other manufacturers, nor would it provide for 

internal averaging between custom and non-custom vehicles in any model year.

Table 3 lists the technologies the agencies are reviewing in the course of the feasibility 

analysis for custom chassis, their associated GEM inputs, and whether they would be available 

inputs under the simplified GEM certification approach. This table is not intended to indicate our

projections of technologies to be applied for specific custom chassis. The vocation-specific 

technology packages we are considering are presented below in Tables 4, 5, and 6. 

Table 3: GEM Inputs

Technology Associated GEM Input Available in Simplified 

GEM or Locked out as 

Default

Low Rolling Resistance Tires CRR level (kg/ton) Available

Idle Reduction Technology

(Stop-Start or Neutral Idle)

Yes or No Available

Part-time Axle Disconnect Yes or No Available

Automatic Tire Inflation System 

(ATIS)

Yes or No Available

Tire Pressure Monitoring System 

(TPMS)

Yes or No Available

Weight Reduction Pounds reduced Available

Coatings to manage solar loads Percent improvement Available

Certified Engine Multi-point fuel map Locked Out

Tire revs/mi Nearest cm Locked Out

Driveline Integration or hybrid 

driveline

Powertrain test results Locked Out

Rear axle ratio 2 decimal places Locked Out

Axle efficiency Multi-point map from 

separate test

Locked Out

Transmission gear ratios 2 decimal places Locked Out

Transmission gear efficiency 2 decimal places Locked Out

Torque converter lockup Gear number Locked Out

Electrified accessories Percent improvement Locked Out

Aerodynamic drag reduction Delta CDA Locked Out
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Technology Associated GEM Input Available in Simplified 

GEM or Locked out as 

Default

Improved PTO operation A-B test results Locked Out

Low-Leak Air Conditioning 

Componentsa

N/A N/A

a Compliance with proposed standards to prevent leakage of HFC from air conditioning systems would be 

demonstrated using another method apart from GEM.

For any model year of the Phase 2 program, a manufacturer of vocational chassis that 

could otherwise qualify to be certified as custom vocational vehicles may elect to certify one or 

more families of vehicles to the primary standards using the full GEM-based program that 

includes engine fuel mapping. Election of this option might include the flexibility to generate 

and trade credits.

We are considering adopting provisions allowing manufacturers of motor home, cement 

mixer, and emergency vehicle chassis to elect to certify one or more families of vehicles to an 

equivalent standard that would not require use of GEM, rather would rely on installation of 

specific technologies. As currently envisioned, this option would not include any averaging, 

banking, or trading provisions. Such equivalent technology-based standards would not be 

available for manufacturers of coach bus, school bus, transit bus, and refuse truck chassis. 

In Tables 4, 5, and 6, the technologies described reflect the kinds of technology projected

to form the basis for possible Phase 2 vehicle standards, and would apply in addition to 

technologies projected to meet the separate engine standard as well as HFC low-leakage 

technologies. Where a tire CRR value is listed for the technology-based packages, the combined 

value is obtained with the following formula: Steer tire CRR x 0.3 + Drive tire CRR x 0.7. 

Table 4: Possible MY 2021 Custom Vocational Vehicle Technology Packages

Vehicle 

Type

Technology-Based Packages Packages with Simplified GEM

Motor Home Combined CRR 6.7 kg/ton or less, and 

Neutral Idle if transmission has torque 

converter, and either TPMS or ATIS

Combined tire CRR 6.1 kg/ton, 30% 

neutral idle, 60% TPMS

Coach Bus N/A HHD combined tire CRR 6.3 kg/ton, 30% 

neutral idle, 50% TPMS, 10% ATIS 

Transit Bus N/A Combined tire CRR 7.7 kg/tona, 50% 

neutral idle, 10% stop-start, 40% TPMS, 

10% ATIS

School Bus N/A Combined tire CRR 6.9 kg/tona, 50% 

neutral idle, 5% stop-start , 70% TPMS

Refuse N/A Combined tire CRR 7.7 kg/ton, 50% 

neutral idle, 10% stop-start, 40% TPMS, 

10% ATIS
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Vehicle 

Type

Technology-Based Packages Packages with Simplified GEM

Emergency Combined tire CRR 8.7 kg/ton or less Combined tire CRR 8.4 kg/ton

Mixer Combined tire CRR 7.6 kg/ton or less Combined tire CRR 7.6 kg/ton

a

 For light heavy-duty transit and school buses, the agencies may allow a manufacturer to multiply the measured 

CRR by 0.87, as is currently allowed for vocational vehicles fitted with LT tires. The baseline data indicate that 

these vehicles have average CRR that is about 13% higher than the average CRR of class 6-8 buses. This would be 

allowable for all years of the Phase 2 program.

Table 5: Possible MY 2024 Custom Vocational Vehicle Technology Packages

Vehicle 

Type

Technology-Based Packages Packages with Simplified GEM

Motor Home Combined CRR 6.7 kg/ton or less, and 

Neutral Idle if transmission has torque 

converter, and either TPMS or ATIS

Combined tire CRR 6.1 kg/ton, 40% 

neutral idle, 70% TPMS

Coach Bus N/A Combined tire CRR 6.1 kg/ton, 40% 

neutral idle, 70% TPMS, 5% ATIS, 5% 

part time 6x2a

Transit Bus N/A Combined tire CRR 7.7 kg/ton, 60% 

neutral idle, 30% stop-start, 45% 

TPMS, 10% ATIS

School Bus N/A Combined tire CRR 6.6 kg/ton, 60% 

neutral idle, 5% stop-start, 90% TPMS, 

5% ATIS

Refuse N/A Combined tire CRR 7.7 kg/ton, 60% 

neutral idle, 30% stop-start, 45% 

TPMS, 10% ATIS

Emergency Combined tire CRR 8.7 kg/ton or less Combined tire CRR 8.0 kg/ton

Mixer Combined tire CRR 7.6 kg/ton or less Combined tire CRR 7.4 kg/ton

a Class 7 and below coach buses that do not have tandem rear axle would be instructed to enter an adjustment factor 

in lieu of part time 6x2 technology.
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Table 6: Possible MY 2027 Custom Vocational Vehicle Technology Packages

Vehicle 

Type

Technology-Based Packages Packages with Simplified GEM

Motor Home Combined CRR 6.0 kg/ton or less, and 

Neutral Idle if transmission has torque 

converter, and either TPMS or ATIS

Combined tire CRR 5.8 kg/ton, 70% 

neutral idle, 90% TPMS

Coach Bus N/A Combined tire CRR 5.8 kg/ton, 70% 

neutral idle, 75% TPMS, 25% ATIS, 30% 

part time 6x2a

Transit Bus N/A Combined tire CRR 6.8 kg/ton, 50% 

neutral idle, 50% stop-start, 40% TPMS, 

30% ATIS

School Bus N/A Combined tire CRR 6.2 kg/ton, 70% 

neutral idle, 15% stop-start, 80% TPMS, 

20% ATIS

Refuse N/A Combined tire CRR 6.8 kg/ton, 50% 

neutral idle, 50% stop-start, 40% TPMS, 

30% ATIS

Emergency Combined tire CRR 8.4 kg/ton or less Combined tire CRR 7.6 kg/ton

Mixer Combined tire CRR 7.1 kg/ton or less Combined tire CRR 7.1 kg/ton

a Class 7 and below coach buses that do not have tandem rear axle would be instructed to enter an adjustment factor 

in lieu of part time 6x2 technology.

Another simplification being considered is to assign each type of custom chassis certified

with simplified GEM to a single weight class that represents the majority of vehicles of that type. 

This would mean that all emergency vehicles, cement mixers, refuse trucks, transit buses, and 

coach buses would be certified with default GEM parameters associated with heavy heavy-duty 

class 8 vehicles, including axle, engine, transmission, tare weight and payload defaults. This 

would also mean that all school bus and motor home chassis would be certified with default 

GEM parameters associated with medium heavy-duty class 6-7 vehicles, including axle, engine, 

transmission, tare weight and payload defaults. Tables 7 and 8 present the default parameters that 

the agencies are planning to program in GEM for these vehicles. The agencies believe that the 

advantages of this simplification would likely outweigh the disadvantages. Specifically, the 

differences in characterization of technology performance between weight classes is very small, 

on the order of tenths of a percent. Further, this would obviate the need for a manufacturer to 

certify multiple vehicle families, where one may have very small sales volumes.
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Table 7: Custom Medium Heavy-Duty Vocational Vehicle Predefined Modeling Parameters

Vehicle Type RV: MHD Regional School Bus: MHD Urban

Engine 7L - 270 hp diesel 7L - 270 hp diesel

Transmission: Forward 

Gears

6-speed automatic: 3.102, 

1.8107, 1.4063, 1, 

0.7117, .61

5-speed automatic: 3.102, 

1.8107, 1.4063, 1, 0.7117

Total Weight (kg) 11,408 11,408

Payload (tons) 5.6 5.6

Number of Axles/Ratio 2 / 4.33:1 2 / 4.88:1

Tire Revs/Mile 517 517

Electrical Accessory Power 

(W)

300 300

Mechanical Accessory 

Power (W)

1,000 1,000

CDA (m2) 5.4 5.4

Tire CRR = 0.7*Drive Crr + 

0.3*Steer Crr

= 0.7*Drive Crr + 

0.3*Steer Crr

Drive Cycles & Weightings:

CARB HHDDT .2 .92

GEM 55 mph cruise with 

road grade

.24 .07

GEM 65 mph cruise with 

road grade

.56 .01

Idle Cycle .22 .33

Table 8: Custom Heavy Heavy-Duty Vocational Vehicle Predefined Modeling Parameters

Vehicle Type Coach Bus: HHD 

Regional

Transit, Refuse, Mixer, 

Emergency: HHD Urban

Engine 11L - 345 hp diesel 11L - 345 hp diesel

Transmission: Forward 

Gears

6-speed automatic: 

4.6957, 2.213, 1.5291, 1, 

0.7643, .6716

5-speed automatic: 4.6957, 

2.213, 1.5291, 1, 0.7643

Total Weight (kg) 19,051 19,051

Payload (tons) 7.5 7.5

Number of Axles/Ratio 3 / 4.33:1 3 / 5.29:1

Tire Revs/Mile 496 496

Electrical Accessory Power 

(W)

300 300

Mechanical Accessory 

Power (W)

1,000 1,000

CDA (m2) 6.86 6.86

Tire CRR = 0.7*Drive Crr + 

0.3*Steer Crr

= 0.7*Drive Crr + 

0.3*Steer Crr
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Vehicle Type Coach Bus: HHD 

Regional

Transit, Refuse, Mixer, 

Emergency: HHD Urban

Drive Cycles & Weightings:

CARB HHDDT .2 .92

GEM 55 mph cruise with 

road grade

.24 .07

GEM 65 mph cruise with 

road grade

.56 .01

Idle Cycle .22 .33

Cost Estimates

Considering the above technology packages and the individual technology costs 

presented in the proposed rulemaking, the agencies estimate the incremental per-vehicle costs for 

custom vocational chassis would be less than the average per-vehicle costs for the broader 

vocational vehicle program.