DOI: 10.15146/r36975
title: Identifying Roadway Physical Characteristics that Contribute to Emissions Differences between Hybrid and Conventional Vehicles

description:   In this study, a second-by-second (SbS) data set obtained from
 monitoring vehicle emissions over a series of 75 test runs from 2 test
 vehicles (a conventional vehicle (CV) and a hybrid-electric vehicle (HEV))
 over an 18-month period in 2010-2011 during real-world on-road operations
 on a specified 32-mile route in Chittenden County, Vermont was used in an
 innovative new method of analysis to assess emissions differences between
 the two propulsion systems and attribute these differences to physical
 roadway/infrastructure characteristics. The K-S test was used to assess
 the difference between the cumulative distributions of the CV and HEV
 emissions samples on each link, and the K-S test statistic was regressed
 against the full set of roadway link characteristics. The regression
 results allowed the team to identify specific roadway characteristics that
 contribute to emissions differences between the vehicle types. Overall,
 the models that included maximum grade and intersection control type
 performed best, however speed limit and horizontal curvature were also
 shown to be important. The performance differences identified in this
 project confirm that engine controls that are responsive to roadway
 characteristics are necessary.
description: This project leveraged
 prior UTC-funded work that developed methods and unique databases of
 second-by-second (SbS) on-board vehicle emissions data for estimating
 emissions differences between conventional vehicles and hybrid-electric
 vehicles. The team used SbS emissions data obtained from a series of 75
 test runs driven by a single driver over 18 months in 2010 and 2011,
 across all seasons and at a variety of hours in the day. The suites of
 emissions data collected during the test runs were isolated by the road
 segment the vehicle was traversing at the time. Spatial processes were
 used to associate the emissions data with the characteristics of the
 roadway on which the vehicle was operating at the time, by assigning each
 emissions data point a Road Segment ID. For each road segment in the
 project, then, the following data is available: 
 ID                    
             TransCAD native feature ID Dir                              
 Link direction: 0 - two-way; 1, -1 - one-way Length                        
 Link length (miles) SP2 Link ID                  Link
 ID corresponding to this study data LINK_NAME                Name of
 roadway represented by the link Daily_Cap                   Daily
 roadway capacity (vehicles per day) Hourly_Cap                Hourly
 roadway capacity (vehicles per hour) SPEED_LIMIT               Speed
 limit (mph) AADT                          
 Annualized Average Daily Traffic for 2010 (from traffic counts)
 AADT/Daily_Cap         AADT
 / Daily roadway capacity GRADE_min                Minimum
 grade (%) on the roadway represented by the link GRADE_max               Maximum
 grade (%) on the roadway represented by the link GRADE_avg                 Average
 grade (%) on the roadway represented by the link HC Degree                  
 Horizontal curvature (degrees) Lane Width                 Lane
 width (ft) Shoulder Width          Right
 shoulder width (ft) Lane + Shoulder          Width of
 the travelled way (lane + shoulder) Median Width             Width of
 the roadway median (null if none) Lanes Each Way          Number of
 lanes of travel in each direction Control_Type            
 Intersection- control / turning-movement type at each end of the link (1
 thru 9) Speed_Limit_Cat        Speed limit
 category (low/high) for cross-classification analysis L+S_Cat                      
 Maximum grade category (negative, flat, low positive, and high positive)
 for cross-classification analysis The distributions of specific SbS
 emissions data were compared using the K-S test, resulting in a D*
 statistics for each link in the study. These data were regressed against
 the physical characteristics above.