June 2015

MEMORANDUM

SUBJECT:	Vocational Vehicle Segmentation and Drive Cycle Development

FROM:	Rafal A. Sobotowski, Engineer, OTAQ/ASD

TO:	Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles - Phase 2 - Docket EPA-HQ-OAR-2014-0827


The first attempt at segmentation of vocational vehicles and the development of representative drive cycles for the respective segments was carried out by the National Renewable Energy Laboratory (NREL) using their Fleet DNA database and the DRIVE analysis tool.  The effort was focused on segmenting vocational vehicles according to the type of operation, namely transient, highway and engine idling.  The most successful approach at this stage consisted of splitting the vocational vehicle fleet into two segments:

   * Stem and Leaf characterized by 30-60% of total distance being driven at highway speeds (defined as >55 mph)
   * Fixed/Local Route distinguished by no more that 15% of total distance being driven at highway speeds
Plots showing the distribution of transient, highway and idling operation across the weight classes and vocations of vehicles with data in NREL's database are provided in Figure 1.  The Stem and Leaf and Fixed/Local Route segments are shown in Figures 2 and 3, respectively.
                                       
Figure 1.  Distribution of transient, highway and idling operation acros weight classes and vocations

                                       
Figure 2:  Distribution of transient, highway and idling operation across the Stem and Leaf segment


                                       
Figure 3:  Distribution of transient, highway and idling operation acros the Fixed/Local Route segment

Once the two segments were defined, NREL's DRIVE tool was used to design the respective transient cycles using vehicle activity data contained in their Fleet DNA database.  The resulting Stem and Leaf and Fixed/Local Route drive cycles are illustrated in Figures 4 and 5.  They were based on test data collected for 103 and 135 vehicles, respectively.  The target duration for these cycles was set at 30 minutes.  For comparison, the reference CARB HHDDT Transient cycle is illustrated in Figure 6.

While Figures 4-6 illustrate NREL's capability to design drive cycles using their DRIVE tool, the underlying vehicle activity datasets were nevertheless deemed insufficient to comprehensively characterize the US fleet of vocational vehicles.

In order to correct this shortcoming, NREL and the EPA have initiated contacts with chassis manufacturers and large vocational vehicle fleets to obtain additional data to fill in the gaps.  This effort is still underway. The final segmentation of the vocational vehicle fleet and generation of drive cycles for the respective segments is expected by the end of 2015.
                                       

                Figure 4:  Candidate Stem and Leaf drive cycle


                                       

                   Figure 5:  Fixed/Local Route drive cycle

                                       
                       Figure 6:  CARB HHDDT drive cycle
      
