This paper describes the use of ordered probit models to examine the risk of different injury levels sustained under all crash types, two-vehicle crashes, and single-vehicle crashes.The results suggest that pickups and sport utility vehicles are less safe than passenger cars under single-vehicle crash conditions. In two-vehicle crashes, however, these vehicle types are associated with less severe injuries for their drivers -and more severe injuries for occupants of their collision partners. Other conclusions also are presented; for example, the results indicate that males and younger drivers in newer vehicles at lower speeds sustain less severe injuries. KEY WORDSAccident/crash modeling, Driver injury, Light-duty trucks, Crashworthiness, Vehicle aggressivity G G

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This work estimates the total safety effects of speed limit changes on high-speed roadways using traffic detector data and Highway Safety Information System (HSIS) data from 1993 to 1996. In order to gauge the total effects, this study applies a sequential modeling approach wherein average speed and speed variance models are first estimated, based on roadway design, use and speed limit information. Then, crash counts (of varying severity) are estimated, based on the speed estimates, design, and use variables. The four years of data come from 63,937 "homogeneous" roadway segments along 7 interstates and 143 state highways in Washington State. A random-effects negative binomial model was selected among several alternative panel and non-panel models for count data. Results indicate that the average road segment in the data set can be expected to exhibit lower non-fatal crash rates up to a 55 mph (88 km/h) speed limit. In contrast, fatality rates appear unresponsive to speed limit changes. Fatal and non-fatal rates fall for design reasons, including wider shoulders and more gradual curves, which appear to be key design variables. However, fatal and non-fatal rates move differently when traffic levels rise, with non-fatal rates remaining unchanged and fatal rates falling.Key Words: Speed limit; Traffic Crash; Panel model; Highway Safety Information System (HSIS) -2 - INTRODUCTIONSpeed limit changes in the U.S. have been made at local and national levels without a thorough understanding of traffic safety consequences. These changes affect speed choices, which affect crash frequency and severity. However, speed choices are only barely recognized in studies aimed at evaluating the effects of speed limit changes on roadway safety. This lack of speed consideration may be attributable to a general lack of extensive speed data.Some speed limit studies have attempted to control for chosen travel speeds by including coarse speed averages and/or variance values (e.g., Rodriguez 1990 andLave 1985). They have relied on highly aggregate speed data (e.g., Rodriquez's [1990] data were at the national level, while Lave's [1985] were at the state level). Such aggregation obscures most distributional information about individual traveler speed choices. Golob and Recker (2003) assembled crash and traffic flow data at the 30-second aggregation level on California highways, yet did not include road design variables.In addition to a lack of chosen speed information, roadway design features are rarely accounted for in speed limit safety studies, although, along with speed, they are recognized as a critical factor in traffic safety. Some speed limit studies (e.g. Lave 1985, Lave and Elias 1994, and Greenstone 2002 have attempted to control for overall design effects by separately analyzing crash counts on different road types (e.g., all interstate, arterial, and collector roads in each state). However, they have failed to include detailed geometric information, primarily due to aggregation of non-homogeneous roadway segments. Again...

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