Intersection and intersection related crashes in all non-limited access roads

In this stage of the analysis, crashes occurring at intersections or within 250 feet of an intersection (influence area defined by DHSMV) for roads not classified as interstates or expressways are considered. The group of drivers involved in intersection crashes was higher than the non-intersection crashes occurring on state non-limited access roads during the year 2004. A total of 64,972 crash involvements were filtered from the 2004 crash records. Statistical

tests of independence and measures of association for the possible contributing factors against the driver injury severity were computed using PROC FREQ, as previously mentioned.

Table 4-10-Preliminary analysis of intersection and intersection related crash driver involvements (N=64,972)

Variable Contingency First Contributing Cause 0.1369 12 4 0.0798 1240.2653 <.0001

Race 0.0548 12 4 0.0317 195.9059 <.0001

Time Group 0.0372 12 4 0.0215 90.2161 <.0001 Lane Group 0.0368 12 4 0.0213 88.2144 <.0001 First Harmful Event 0.172 16 5 0.0873 1979.6119 <.0001 Vehicle Movement 0.0993 32 5 0.0499 647.0668 <.0001 First Traffic Control 0.0798 16 5 0.0400 416.4241 <.0001 Driver Age Group 0.0751 28 5 0.0377 368.8244 <.0001 Number of Lanes 0.055 20 5 0.0276 197.3873 <.0001

The results of this analysis, shown in Table 4-10 above, illustrate some of the important differences when considering intersection crashes as` opposed to non-intersection crashes. The weather nor the off roadway variables are no longer significant at the 5% significance level.

There were additional differences in the measures of association for the rest of the variables.

There is a much stronger association of driver injury severity with gender and vehicle fault code

character, location type, speed limit group, type of shoulder, lane groups, location on roadway) loose association strength. . Meanwhile, two of the driver-related variables (speeding and alcohol-drugs) lost association strength. This suggests that the severity of driver injury resulting from crashes occurring at intersections tends to be more influenced by the drivers’ actions than non-intersection crashes.

Table 4-11 Ejected and injury severity cross tabulation table for non-intersection involvements Ejected Driver Injury Level

Frequency

The statistics in Table 4-11 above show that ejection events at intersection or intersection related crashes (2.74%) are proportionally lower than for the non-intersection crashes (3.59%).

When the ejection event occurs, intersection or intersection related crashes injury outcomes comprise 38% and 13.5% of the fatal and incapacitating injuries, respectively. This suggests that in general crashes occurring at or near intersection are les likely to produce driver ejection and less likely to result in severe injury to those who are ejected from the vehicle. This comparison points out that crashes on segments are more likely to result in ejection, perhaps due to the single vehicle off-roadway crashes, which tend to be severe. The differences in crash mechanisms at segments and intersections are evident; however, the ejection event is still a very important factor that is present in 18.3% of all of the involvements under analysis (intersection and non-intersection).

Table 4-12 Urban land use and injury severity cross tabulation table for non-intersection involvements Urban_ID Driver Injury Level

Frequency

(Row Percent) PDO Possible

Injury Evident

The land use might be considered the most encompassing factor that deals with traffic behavior and road design. A shown in Table 4-12 above, the urban involvements are higher than the rural involvements. The rural involvements have a higher proportion of severe injury. While 41% of the involvements occur in rural areas, these represent 54% and 67.8% of the incapacitating and fatal injuries. Thus, similar to the segments, the rural sections of road present a serious trend of more severe injuries due to crashes. If the lower intersection density in rural areas is considered, there is some evidence of significantly higher severe crash rates at those rural intersections when compared to their urban counterparts.

Non-intersection Intersection and intersection related

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In comparing the intersections and non-intersection environments, we consider two important factors of the drivers involved in crashes: age and gender. The distribution of severe involvements by driver age group divided in non-intersection and intersection events are shown in Figure 4-1 above. While the non-intersection involvements exhibit an increasing proportion of severe injuries by driver age for the older drivers (65-79 years) and a reduction for the very old drivers (80 and above). On the other hand, for the intersection crashes the proportion of severe injuries for the younger drivers are lower than middle age drivers (25-64 years), but the older and very old drivers showed a significantly higher proportion. These statistics suggests that older drivers are the group a greatest risk of severe injuries. Meanwhile, the other age groups seem to be at greater severe injury risk in road segments.

Non-intersection Intersection and intersection related

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Figure 4-2 - Severe involvements in non-limited access roads by driver gender and road entity

Driver gender affects the crash outcomes because of both the physiological and behavioral differences between males and females. The statistics in Figure 4-2 above show that female have more involvements in both types of crashes for the severe injury crashes. This

preliminary analysis suggests the theory that females are more likely to suffer serious injury as a result of a crash event. Additional analysis in chapter 5 will show these relationships applied exclusively to multilane high-speed roads.

The decreased association performance of the road-related factors should be analyzed in the context of the lack of intersection characteristics among the variables under analysis. As discussed in Section 2.4.1, additional intersection characteristics are needed to describe the safety performance of this road entity. Previous research by Abdel-Aty and Wang (2006) has shown that intersections present complex driving situations, especially in urban areas. Thus, drivers are required a greater degree of concentration and ability to traverse in a safely manner.