### UNITED STA **TES ENVIRONMENTA L PROTECTION A**  **GENCY**

NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY

2565 PLYMOUTH ROAD ANN ARBOR, MI 48105

- 2498

OFFICE OF

AIR AND RADIATION



### May 8 , 2015

MEMORANDUM

SUBJECT: Analy sis of Possible Vocational Vehicle Standards Based on Alternative Id le Cy cle

Weightings

FROM: Lauren Steele

, Environmental Engineer, OTAQ/ASD

TO: Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium

- and

Heav y

- Duty

Engines and Vehicles

- Phase 2

- Docket EPA

- HQ

- OAR

- 201 4

- 0827

**Introduction**

Th is memorandum presents estimated emission reductions and fuel consumption savings based

on alternate weightings of the proposed GEM idle cy cle for vocational vehicles

. Depending on additional information that may become available during the comment period, it is possible that the agencies may

change the weighting of the idle cy cle in the composite GEM cy cles for vocational

vehicle s from the proposed values to values that better reflect real world vocational vehicle operation. This memo explores the effects of such change on technology effectiveness and vehicle performance, as

simulated through GEM.

In GEM the emissions and fuel consumed during the idle cy cle are time

- based (grams or gallons per hour), and the distance

- based emissions and fuel consumed while moving (grams or gallons per ton

mile) are calculated separatel y. Because the combined weightings of the three distance

- based cy cles plus the idle cy cle total 100 percent, any increase in the weighting of idle cy cle emissions causes a proportional decrease in weighting of the emissions while moving. This means that the degree of

we ighting of the idle cy cle influences the relative importance of idle reduction technology compared with technologies that reduce emissions while driving. For example, an increase in idle cy cle weighting would lead to a smaller relative importance of techno logies that reduce engine emissions and rolling

resistance.

**Range of Idle Cycle Weightings** 

According to preliminary work by the National Renewable Energy L aboratory

(NREL) , logged activity of vehicles in the NREL database indicates the overall percent of idle time ranges between eight and 50 percent, with most vehicles logging idle time between 18 and 33 percent. Figure 1 shows an example summary

of some NREL idle operation data for vocational vehicles.

### 2 **Figure 1**  **: Percent Idle**  **Time p**  **er Day p**  **er Vehicle. So**  **urce: NREL**



### Using the GEM tool, the agencies have estimated the effectiveness of workday idle reduction technology

(neutral idle and stop

- start) across a wide range of idle cy cle weightings. Figure s 2 and 3 present the estimate d effectiveness of neutral idle and stop

- start, respectively , for idle cy cle weightings up to 50 percent. The proposal case weights all weight classes of Regional vehicles at 10 percent idle,

Multi

- purpose vehicles at 15 percent idle, and Urban vehicles a t 20 percent idle , regardless of engine

ty pe

. For each curve in the graph , the percent reduction from the GEM baseline is calculated from a baseline that uses the same weighting of idle as for the idle reduction technology case. For example, at 30 percen t idle cy cle weighting, a MHD Urban vehicle with neutral idle would have a GEM score 5.5 percent lower than a baseline vehicle with that same idle cy cle weighting

.

**Figure 2**  **: Change in Effectiveness of Neutral Idle Workday Idle Reduction Technology with Cycle Weighting** 

0% 2% 4% 6% 8% 10% 12%**P e** **r c** **e n** **t R** **e d** **u c** **t i** **o n** **f r** **o m** **G E** **M B** **a s** **e l** **i n** **e**

**Relative Percent Weighting of Idle Cycle (%)**  

# Sweep of Possible **Neutr al Idle R**  **eductions**

HH Regional

HH Multipurpose

HH Urban

MH Regional

MH Multipurpose

MH Urban

LH Regional

LH Multipurpose

LH Urban

### 3

**Figure 3**  **: Change in Effectiveness of Stop**

**- Start Workday Idle Reduction Technology with Cycle Weighting** 



### Figure 4 presents the relative contribution to GEM baseline values (no added tech nology and all vehicles idling at CITT emission rates ) as the weighting of the idle cy cle changes from zero to 50

percent . The emission rates in grams of CO 2 

### per ton

- mile decrease with increasing idle weighting due to

the relativel y lesser weighting of emi ssions over the ARB transient, 55 mph cruise and 65 mph cruise

cy cles. In the example of the H HD Urban vehicle (dark green bars on the graph) , the contribution of the ARB Transient cy cle is about 40 percent of the total mass of CO 2 

### in g/ton

- mi when the idl e cy cle is weighted zero (first cluster of bars). In the case of a 30 percent idle cy cle weighting, the transient

contribution from this same HHD Urban vehicle would be about 36 percent of the total mass of CO 2 

### in

g /ton

- mi

. 0%

5% 10% 15% 20% 25%**P e** **r c** **e n** **t R** **e d** **u c** **t i** **o n** **f r** **o m** **G E** **M B** **a s** **e l** **i n** **e**

**Relative Percent Weighting of Idle Cycle (%)**  

# Sweep of Possible **Stop**

**- Start Idle R**  **eductions**

HH Regional

HH Multipurpose

HH Urban

MH Regional

MH Multipurpose

MH Urban

LH Regional

LH Multipurpose

LH Urban

### UNITED STA **TES ENVIRONMENTA L PROTECTION A**  **GENCY**

NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY

2565 PLYMOUTH ROAD ANN ARBOR, MI 48105

- 2498

OFFICE OF

AIR AND RADIATION

**Figure 4**  **: Change in Baseline Perform ance with Idle Cycle Weighting**  0% 5% 10% 15% 20% 25% 30% 35% 40% 45%Transient55mph65mphIdleTransient55mph65mphIdleTransient55mph65mphIdleTransient55mph65mphIdleTransient55mph65mphIdleTransient55mph65mphIdle**P e** **r c** **e n** **t C** **o n** **t r** **i b** **u t** **i o** **n t** **o G** **E M** **C o** **m p** **o s** **i t** **e W** **e i** **g h** **t e** **d M** **a s** **s o** **f C** **O 2** **g /** **t o** **n -** **m i** 

**Test Cycles with Idle Cycle Weightings from Zero to 50%**  HH Regional HH Multipurpose HH Urban MH Regional MH Multipurpose MH Urban LH Regional LH Multipurpose LH Urban



### Proposed

10

- 15

- 20

20% Idle 30% Idle

40% Idle 50% Idle Zero Idle