MIDDLE EAST TECHNICAL UNIVERSITY 1 Shashi Nambisan Institute for Transportation Iowa State University Murat Ozen Middle East Technical University Department.

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Presentation transcript:

MIDDLE EAST TECHNICAL UNIVERSITY 1 Shashi Nambisan Institute for Transportation Iowa State University Murat Ozen Middle East Technical University Department of Civil Engineering Mid-Continent Transportation Research Symposium Ames, IA August 15, 2013 An Exploratory Analysis of Large Truck Crashes in the US

MIDDLE EAST TECHNICAL UNIVERSITY 2 Introduction Truck operations: Key for trade & commerce – Disproportionate share of fatal crashes Safety analysis: Macro-level; Fatal crash rates – Outcomes: Number and type of crashes – Exposure measures: #Trucks, Travel, Type & Extent of Roads Analyses of truck safety records: 2000 to 2010 Definitions of trucks before and after 2007 (US DOT) Fatal truck crash analysis – Spatial considerations – Temporal considerations

MIDDLE EAST TECHNICAL UNIVERSITY 3 Methodology Large truck fatal crash rates per 100 million VKT Annual rates – At national level – At regional level for the US DOT’s 10 federal regions Descriptive analyses Statistical tests

MIDDLE EAST TECHNICAL UNIVERSITY 4 Data Sources US DOT – Federal Highway Administration (FHWA) – Federal Motor Carrier Safety Administration (FMCSA) Large trucks = Gross vehicle weight rating or gross combination weight rating of more than 4.5 tons National level fatal crash and truck Vehicle Kilometer of Travel (VKT) data available for the study period State level truck VKT data available only 2009, 2010 – Average % of national VKT for each state in 2009, 2010 – Apply to national VKT for the years 2000 to 2008

National Level Trends % registered trucks in national vehicle fleet increased from 3.5% in 2006 to 4.2% in 2007 Truck VKT increased 36.7% in 2007 as compared to 2006 Truck fatal crash rate per 100 million vehicle kilometers traveled by large trucks decreased from 1.21 to 0.86 Year Fatal Crashes Million Truck VKT Fatal Crash Rate per 100 Million VKT 20004,573330, ,451336, ,224345, ,335350, ,478355, ,551358, ,350358, ,204489, ,754499, ,987463, ,261461, MIDDLE EAST TECHNICAL UNIVERSITY

6 Check Data for Normality Shapiro-Wilk normality test for normality assumption – H o : The data are normally distributed – H 1 : The data are not normally distributed PeriodDataTest StatisticdfSignificance Reject Ho (95%)? Before 2007 National YES Urban YES Rural YES After 2007 National YES Urban YES Rural YES Shapiro-Wilk Normality Tests Results For National Level Fatal Truck Crash Data Need to use non-parametric statistical methods

MIDDLE EAST TECHNICAL UNIVERSITY 7 Non-Parametric Tests Wilcoxon Rank-Sum test and Mann-Whitney U test –to test the null hypothesis that two populations are the same Kruskall-Wallis H test –to test the null hypothesis that more than two populations are the same

MIDDLE EAST TECHNICAL UNIVERSITY 8 Urban vs. Rural Are the Urban & Rural fatal truck crash rates the same before and after 2007? o Before 2007 (i.e. Average rural = 1.63 > Average urban = 0.84) o After 2007 (i.e. Average rural = 0.94 > Average urban = 0.52) Ho: Urban and rural fatal truck crash rates are the same H1: Urban and rural fatal truck crash rates are NOT the same HypothesisTest Type Test Statistics (ts)/ Z-Value Critical Value Reject Ho (95%) BEFORE 2007 W R-S (ts)28L=36YES M-W U (Z) YES AFTER 2007 W R-S (ts)10L=11YES M-W U (Z) YES Reject WR-S test Ho if ts U Reject M-W U test Ho if absolute value of z > z C Rural fatal truck crash rates are higher than urban fatal truck crash rates

MIDDLE EAST TECHNICAL UNIVERSITY 9 Roadway Types Compare fatal truck crash rates for interstate highways, other arterials and other highways before and after 2007 Interstate highways have lower fatal crash rates than other types of roadways. Are the differences in fatal crash rates on interstates and other arterials and other arterials and other highways statistically significant?

MIDDLE EAST TECHNICAL UNIVERSITY 10 Roadway Type Comparisons Ho: Fatal truck crash rates are the same for interstate highways, other arterials and other highways H1: Fatal truck crash rates are NOT the same for interstate highways, other arterials and other highways HypothesisTest Type Test Statistics (ts) Critical Value Reject Ho (95%) BEFORE 2007K-W H (ts) YES AFTER 2007K-W H (ts) YES Reject K-W H test Ho if H > Hcritical

MIDDLE EAST TECHNICAL UNIVERSITY 11 Regional Trends: Before 2007 Fatal crash rate in Region 4 is the highest Fatal crash rate in Region 10 is the is lowest Fatal crash rates in Region 3, Region 8 and Region 10 seem to be lower than the others

MIDDLE EAST TECHNICAL UNIVERSITY 12 Regional Trends: After 2007 Fatal crash rate in Region 4 is the highest Fatal crash rate in Region 10 is the is lowest Variations in the fatal truck crash rates across the regions are not pronounced

MIDDLE EAST TECHNICAL UNIVERSITY 13 Regional Comparisons: Pairwise Fatal truck crash rates are not the same for different regions before and after 2007 based on pairwise comparisons. Ho: Fatal truck crash rates are the same for each region H1: Fatal truck crash rates are NOT the same for each region Hypothesis Test Type Test Statistics (ts) Critical Value Reject Ho (95%) BEFORE 2007 K-W H (ts) YES AFTER 2007 K-W H (ts) YES Reject K-W H test Ho if H > Hcritical

MIDDLE EAST TECHNICAL UNIVERSITY 14 Regional Ranks: Before 2007

MIDDLE EAST TECHNICAL UNIVERSITY 15 Regional Ranks: After 2007

MIDDLE EAST TECHNICAL UNIVERSITY 16 State Level Analyses Comparison of state level fatal truck crash rates across the states before and after 2007 Ho: Fatal truck crash rates are the same across the states H1: Fatal truck crash rates are NOT the same across the states Hypothesis Test Type Test Statistics (ts) Critical Value Reject Ho (95%) BEFORE 2007 K-W H (ts) YES AFTER 2007 K-W H (ts) YES Reject K-W H test Ho if H > Hcritical

MIDDLE EAST TECHNICAL UNIVERSITY 17 State Level Ranks: Before 2007

MIDDLE EAST TECHNICAL UNIVERSITY 18 State Level Ranks: After 2007

MIDDLE EAST TECHNICAL UNIVERSITY 19 Summary Illustrated methods to analyze truck safety – Non-parametric techniques Variations in fatal truck crash rates – Before and after 2007 – Urban vs rural – Across roadway types – Across federal regions – Across states – Northwest US vs Southeast US Limitations – Focused only on fatal truck crash rates – Need to evaluate other factors / metrics

MIDDLE EAST TECHNICAL UNIVERSITY 20 Implications Spatial and temporal variations in truck safety records warrant further study Changes in truck definitions affected estimated crash rates – Use caution when comparing Pre-2007 and Post data Method can be adapted for safety analyses in other contexts Support policy making – Planning – Design – Operations – Law enforcement strategies – Resource allocation – Others

MIDDLE EAST TECHNICAL UNIVERSITY 21 Contact Information Shashi Nambisan, Ph.D., P.E. Professor of Civil Engineering Institute for Transportation Iowa State University Ames, IA Murat Ozen, Ph.D. Candidate Middle East Technical University Department of Civil Engineering 06800, Ankara - TURKEY