From: "Debbie L. Gordon" <debbie.gordon@allisontransmission.com>

To: Byron Bunker/AA/USEPA/US@EPA

Date: 05/16/2011 05:31 PM

Subject: RE: Your questions from Wednesday

Byron,

Thank you for getting back to me. I appreciate the information with regard to the calculation of g/mile 

or ton-mile calculation but to clarify on my previous question, we have been trying to determine how 

the drive cycle weightings were developed for transient and steady state operations at 55 mpg and 65 

mpg. We have looked at preamble, RIA and supporting documents that are in the docket, but cannot 

determine whether the weightings themselves were based on time or distance; i.e., whether the 

percentages are derived from data representing the relative amount of time a vehicle spends at these 

mpg's, or the amount of distance that vehicles travel at these steady state modes. Could you clarify as 

to the source of the data and the basis for the calculation? I have some examples shown below that get 

to the nature of our questions. If you can reply in advance before Thursday, that would be great, but if 

not, we can discuss face-to-face. Thank you again.

Best regards,

Debbie

One source of confusion is found in the RIA:

Oak Ridge National Laboratory evaluated the fuel efficiency effect of tires on Class 8 heavy

trucks. The estimation is based on FHWA’s Highway Statistics and the Census Bureau’s 

Vehicle In-Use Survey (VIUS). The study found that Class 8 sleeper cabs use an average of 

6.8% of their fuel idling. 19 The study collected fleet data related to real-world highway

environments over a period of two years. The fleet consisted of six trucks which operate widely 

across the United States. In the Transportation Energy Data Book (2009)20 Table 3-5: 

Combination Tractor Drive Cycle Weighting Table 5.11 was analyzed and found on average that 

the line haul trucks spent 5% of the miles at speeds less than 50 mph, 17% between 50 and 60 

mph, and 78% of the time at speeds greater than 60 mph. 

The text highlighted in red appears to be weighted on distance whereas the text in green appears to be 

weighted on time. Additionally, when the drive cycle is described for hybrids, with and without PTO, it is 

also confusing if it is to be distance-based because the PTO operation would have to be based on time 

since the vehicle is stationary during that operation.

The Figure below was submitted as Attachment 4 in our comments. As you can see, the results of these 

calculations can be very different when considering % time vs. % distance. 
From: Bunker.Byron@epamail.epa.gov [mailto:Bunker.Byron@epamail.epa.gov] 

Sent: Friday, May 13, 2011 4:57 PM

To: Debbie L. Gordon

Cc: Jackson.Cleophas@epamail.epa.gov

Subject: Your questions from Wednesday

Hi Debbie,

I am sorry that it has taken me so long to respond. Here are my responses to your questions from our 

call Wednesday.

1) Can EPA update Allison on our testing and reasons for wanting to retest? The person best able to talk 

about the completed testing will be on travel on the 18th. We are trying to find someone else that can 

walk us through the results. I will confirm on Monday if we will be able to go through the test results. We 

will definitely be able to explain our reasons for retesting.

2) Are the EPA drive cycles time based or distance based? The vehicle drive cycles are expressed as 

speed versus time. However it is the actual distance traveled (either literal chassis roll revolutions or 

integrated actual attained speed) that determines the distance used in the g/mile or ton-mile calculation. 

So the vehicle does it best to follow a speed vs time trace, but the actual distance traveled is what is used 

in determining the compliance metric.

3) Can EPA respond to questions i-x on pages 37-38 of Allison's comments? Since most of the 

questions are comments on the proposal and not simply questions for information, I would prefer to talk 

about the issues raised by the questions during our meeting on the 18th.

Thanks,

Byron

******************************************************************

Byron Bunker

Center Director - Heavy-Duty Onroad Center

Assessment and Standards Division

Office of Transportation and Air Quality

US Environmental Protection Agency

2000 Traverwood Drive

Ann Arbor, MI 48105

(734) 214-4155

(734) 214-4050 (fax)

(734) 353-9623 (cell)

e-mail: bunker.byron@epa.gov

**********************************************************