CHAPTER 2: COMPARISON OF THE RESULTS FROM THE ANALYSES CONDUCTED WITH THE 100-Car Data and the LOCAL/SHORT HAUL AND SLEEPER BERTH DATA

Recall in Chapter 1 that analyses were conducted with critical incident data that were collected during the 100-Car Study (Dingus et al., 2004). The method of analysis used in Chapter 1 is almost identical to the approach used in Hanowski, Keisler, and Wierwille (2004). The Hanowski, Keisler, and Wierwille (2004) study assessed LV-HV interactions from the perspective of local/short-haul (L/SH) and sleeper berth (SB) drivers. A total of 142 LV-HV interactions were identified in the L/SH study (see Hanowski, Wierwille, Garness, and Dingus, 2000, for a complete description of the L/SH study). Of these, 117 (82.4%) incidents were judged to have been the fault of the LV driver, while the remaining 25 (17.6%) incidents were the fault of the HV driver (remember that incidents in the L/SH and SB studies used "initiate" to indicate fault. From this point on, "at-fault" will be used rather than "initiate").

In the SB study, a total of 68 LV-HV interactions were identified (see Dingus et al., 2002, for a complete description of the SB study). Of these, 47 (69.1%) were assessed to have been the fault of the LV driver, while the remaining 21 (38.9%) were the fault of the HV driver. Taken together with the current research, these three studies consistently show that LV drivers appear to be responsible for the majority of LV-HV interactions. Of the 427 LV-HV incidents identified across the three studies (excluding the 29 Unknown at-fault incidents in the current study), 302 (70.7%) were the fault of the LV driver, while the remaining 125 (29.3%) were the fault of the HV driver (a 2.4:1 ratio).

However, one of the weaknesses in the current study was the lack of instrumentation in HVs. Conversely, one of the weaknesses in the Hanowski, Keisler, and Wierwille (2004) study was the lack of instrumentation in LVs. Thus, by integrating the results from the present study with the results from the Hanowski, Keisler, and Wierwille (2004) study, it is believed that a more complete understanding of LV-HV interaction problem can be gained. Chapter 2 has two primary aims: combine the data from the current study with the data from the L/SH and SB studies in Hanowski, Keisler, and Wierwille (2004) to illustrate the overall LV-HV interaction picture, and address the limitation of having only one vehicle instrumented by assessing the differences between the three studies (i.e., are the recorded LV-HV interactions fundamentally different as a function of which vehicle is instrumented?).

Incident Types

Table 34 illustrates the frequency, percentage, and rank ordering of Incident Types across all three studies. As can be seen in Table 34, there were a total of 456 LV-HV interactions across the three studies. The most frequent Incident Type was Lane Change Without Sufficient Gap (22.1%), followed by Late Braking for Stopped/Stopping Traffic (17.3%) and Roadway Entrance Without Clearance (7.9%). Figure 34 shows a bar graph of the 456 incidents, across the three studies, as a function of Incident Type.

Table 34. Frequency, Percentage, and Rank Ordering of the Incident Types

Across the Three Studies.

Figure 34. Percentage of Incident Types Across all Three Studies.

Tables 35-37 show the frequency and percentage of each Incident Type in the 100-Car, SB, and L/SH studies, respectively. In the 100-Car Study, the most frequent Incident Types were Late Braking for Stopped/Stopping Traffic (26.8%), Lane Change Without Sufficient Gap (22%), and Lateral Deviation of Through Vehicle (8.1%) . In the SB study, the most frequent Incident Types were Lane Change Without Sufficient Gap (25%), Turn Without Sufficient Warning (17.6%), Late Braking for Stopped/Stopping Traffic (14.7%). In the L/SH study, the most frequent Incident Types were Lane Change Without Sufficient Gap (21.1%), Roadway Entrance Without Clearance (14.3%), and Left Turn Without Clearance (14.8%). Figure 35 shows a bar graph that illustrates the percentage of incidents in the 100-Car, SB, and L/SH studies as a function of the Incident Types.

Table 35. Frequency and Percentage of Incident Types for the 100-Car Study.

Table 36. Frequency and Percentage of Incident Types for the Sleeper Berth Study.

Table 37. Frequency and Percentage of Incident Types for the Local/Short Haul Study.

Figure 35 . Percentage of Incident Types in the 100-Car, SB, L/SH Studies.

Figure 36 shows the percentage of HV driver at-fault incidents in the 100-Car, SB, and L/SH studies as a function of Incident Type. The black bars in Figure 36 represent HV driver at-fault incidents in the 100-Car data set, while the white and grey bars represent SB and L/SH driver at-fault incidents, respectively. The most frequent Incident Types for HV driver at-fault incidents in the 100-Car Study were Lane Change Without Sufficient Gap (26.6%), Lateral Deviation of Through Vehicle (21.5%), and Left Turn Without Clearance (13.9%). The most frequent Incident Types for HV driver at-fault incidents in the SB study were Late Braking for Stopped/Stopping Traffic (47.6%), Following Too Close (23.8%), and Turn Without Sufficient Warning (14.3%). The most frequent Incident Types for HV driver at-fault incidents in the L/SH study were Roadway Entrance Without Clearance (20%), Backing In Roadway (12%), Late Braking for Stopped/Stopping Traffic (12%), Wide Turn Into Adjacent Lane (12%), and Low Speed (8%).

).

Figure 36 . Percentage of HV Driver At-Fault Incident Types in the 100-Car, SB, and L/SH Studies.

Figure 37 shows the percentage of LV driver at-fault incidents in the 100-Car, SB, and L/SH studies as a function of Incident Type. The black bars in Figure 37 represent the 100-Car driver at-fault incidents in the 100-Car Study, while the white and grey bars represent LV driver at-fault incidents in the SB and L/SH data sets, respectively. The most frequent Incident Types for LV driver at-fault incidents in the 100-Car Study were Late Braking for Stopped/Stopping Traffic (41.3%) Lane Change Without Sufficient Gap (21.7%), and Aborted Lane Change (8%). The most frequent Incident Types for LV driver at-fault incidents in the SB study were Lane Change Without Sufficient Gap (32%), Turn Without Sufficient Warning (19.1%), and Low Speed (17%). The most frequent Incident Types for LV driver at-fault incidents in the L/SH study were Lane Change Without Sufficient Gap (24.8%), Roadway Entrance Without Clearance (17.9%), Turn Without Clearance (17.9%), and Improper Passing (5.1%).

Figure 37 . Percentage of LV Driver At-Fault Incident Types in the 100-Car, SB, and L/SH Studies.

As can be seen in Figure 37, the Incident Types differed markedly depending on the study (i.e., 100-Car, SB, and L/SH). One possible explanation for these discrepancies could be the frequency of travel on certain Road Types (i.e., it would be expected that a significant amount of the incidents would occur on the most traveled roadways, similar to exposure). Of course, this is an oversimplification. The geographical area, what the vehicle was used for, and driver preference all dictate the predominant Road Type used in driving. Figure 38 illustrates the percentage of incidents for each of the three studies as a function of Road Type. The black bars in Figure 38 represent 100-Car incidents, while the white and grey bars represent SB and L/SH incidents, respectively. In the 100-Car data set, the highest proportion of incidents occurred on the Urban Divided (60.2%), Urban Undivided (18.7%), and Rural Undivided (9.3%) roads. In the SB data set, the highest proportion of incidents occurred on the Rural Divided (55.9%), Urban Undivided (10.3%), and Rural Undivided (13.2%) roads. In the L/SH data set, the highest proportion of incidents occurred on the Rural Divided (38.7%), Urban Undivided (18.3%), and Rural Undivided (16.2%) roads.

Figure 38 . Percent of Incidents in the 100-Car, SB, and L/SH studies as a Function of Road Type.

Summary of Incident Types

Across the three studies, the most frequent Incident Types were Lane Change Without Sufficient Gap (22.1%), Late Braking for Stopped/Stopping Traffic, (17.3%), and Roadway Entrance Without Clearance (7.9%). These three Incident Types accounted for 47.3% of LV-HV interactions across the three studies.

As can be seen in Figure 36, the HV driver at-fault Incident Types differed with respect to the instrumented vehicle. The most frequent Incident Types for HV driver at-fault incidents in the 100-Car Study were Lane Change Without Sufficient Gap (26.6%), Lateral Deviation of Through Traffic (21.5%), and Left Turn Without Clearance (13.9%). These three Incident Types represented 62% of the HV driver at-fault incidents in the 100-Car Study. The most frequent Incident Types for HV driver at-fault incidents in the SB study were Late Braking for Stopped/Stopping Traffic (47.6%), Following Too Closely (23.8%), and Turn Without Sufficient Warning (14.3%). These three Incident Types represented 85.7% of the HV driver at-fault incidents in the SB study. The most frequent Incident Types for the HV driver at-fault incidents in the L/SH study were Roadway Entrance Without Clearance (20%), Wide Turn Into Adjacent Area (12%), and Backing in Roadway (12%). These three Incident Types represented 48% of HV driver at-fault incident in the L/SH study.

As can be seen in Figure 37, the LV driver at-fault Incident Types also differed with respect to the instrumented vehicle. The most frequent Incident Types for LV driver at-fault incidents in the 100-Car Study were Late Braking for Stopped/Stopping Traffic (41.3%) and Lane Change Without Sufficient Gap (21.7%). These two Incident Types represent 63% of the LV driver at-fault incidents in the 100-Car Study. The most frequent Incident Types for LV driver at-fault incidents in the SB study were Lane Change Without Sufficient Gap (31.9%), Turn Without Sufficient Warning (19.1%), and Low Speed (17%). These three Incident Types represent 68% of the LV driver at-fault incidents in the SB study. The most frequent Incident Types for the LV driver at-fault incidents in the L/SH study were Lane Change Without Sufficient Gap (24.8%), Roadway Entrance Without Clearance (17.9%), and Left Turn Without Clearance (17.9%). These three Incident Types represent 60.6% of LV driver at-fault incident in the L/SH study.

There were many differences across the three studies (100-Car, L/SH, and SB) as well between HVs and LVs within each study. This is possible as both the SB and L/SH trucks were instrumented in their respective studies, while the LV was instrumented in the 100-Car Study. Thus, those incidents recorded in the 100-Car Study reflect a diverse range of HVs. Further, the incidents in the SB and L/SH studies are likely to reflect difficulties specific to SB and L/SH operations. Support for this hypothesis was found when the authors assessed the location of each incident (see Figure 38).

Consider the Road Type comparison data shown in Figure 38. The bar graph illustrates the percentage of incidents as a function of different Road Types. Not surprisingly, the Road Types frequented by the 100-Car participants, such as major city roads and streets, are where the majority of 100-Car Study incidents occurred (60.2% of the incidents occurred on an Urban Divided road). The Road Types common to SB operations, such as interstates and highways, are where the majority of SB incidents occurred. That is, rural divided by median (i.e., interstate) and urban divided by median (i.e., highway) accounted for 74% of the SB incidents. Similarly, the Road Types common for L/SH trucks accounted for many of the L/SH incidents. On a percentage basis, there were more incidents for L/SH drivers in town settings (i.e., urban undivided, urban divided, one-way, and parking lot), which is where many L/SH delivery routes are located. By looking at the driving environments, it could be said that the majority of 100-Car and L/SH incidents occurred in and around town/urban areas (lower speeds and higher traffic areas). SB incidents, on the other hand, tended to occur on highways where speeds are relatively high and traffic density is relatively low.

For example, Roadway Entrance Without Clearance accounted for a substantial portion of L/SH incidents (18.3%), whereas this Incident Type only accounted for a small proportion of the incidents in the 100-Car (2.4%) and SB (5.9%) studies. This makes intuitive sense when one considers L/SH operations trucking operations. L/SH drivers have many deliveries during their workday and will, therefore, routinely exit parking lots onto roadways. This provides an opportunity for this particular Incident Type to occur, whereas this maneuver is not characteristic of 100-Car and SB drivers. Much of the time, SB drivers were on limited-access highways having no intersecting side roads, whereas 100-Car drivers were driving on major urban road going to and from their residence. The characteristics of the Road Types traveled by 100-Car, SB, and L/SH drivers appear to explain some of the discrepancies between the three studies.

Primary Maneuvers

Table 38 shows the frequency, percentage, and rank ordering of the Primary Maneuvers across the 100-Car, SB, and L/SH studies. The most frequent Primary Maneuver across all three studies was Changing Lanes (23.2%), followed by Braking (12.3%) and Left Turn (11.2%). Figure 39 shows a bar graph of the 456 incidents, across the three studies, as a function of Primary Maneuver.

Table 38. Frequency, percentage, and rank ordering of Primary Maneuvers across the three studies.

Figure 39 . Frequency of Primary Maneuvers Across the Three Studies.

Tables 39-41 show the frequency and percentage of each Primary Maneuver in the 100-Car, SB, and L/SH studies, respectively. In the 100-Car Study, the most frequent Primary Maneuvers were Braking (22.8%), Changing Lanes (21.1%), and Stopped (15%) . In the SB study, the most frequent Primary Maneuvers were Through Traffic (39.7%), Changing Lanes (32.4%), Roadway Exit (8.8%), and Left Turn (8.8%). In the L/SH study, the most frequent Primary Maneuvers were Changing Lanes (22.5%), Left Turn (20.4%), and Through Traffic (19%). Figure 40 shows a bar graph illustrating the incidents for the 100-Car, SB, and L/SH studies as a function of Primary Maneuver.

Table 39. Frequency and Percentage of Primary Maneuvers for the 100-Car Study.

Table 40. Frequency and Percentage of Primary Maneuvers for the Sleeper Berth Study.

Table 41. Frequency and Percentage of Primary Maneuvers for the Local/Short Haul Study.

Figure 40 . Percentage of Primary Maneuvers in the 100-Car, SB, and L/SH Studies.

Figure 41 shows the percentage of HV driver at-fault incidents in the 100-Car, SB, and L/SH studies as a function of Primary Maneuver. The black bars in Figure 41 represent the HV driver at-fault incidents in the 100-Car Study, while the white and grey bars represent HV driver at-fault incidents in the SB and L/SH studies, respectively. The most frequent Primary Maneuvers for HV driver at-fault incidents in the 100-Car Study were Changing Lanes (32.9%), Crossing Over Lane Line (26.3%), and Left Turn (15.2%). The most frequent Primary Maneuvers for HV driver at-fault incidents in the SB study were Through Traffic (71.4%), Changing Lanes (9.5%), and Left Turn (9.5%). The most frequent Primary Maneuvers for HV driver at-fault incidents in the L/SH study were Through Traffic (44%), Right Turn (24%), and Left Turn (12%).

Figure 41 . Percentage of HV Driver At-Fault Incidents in the 100-Car, SB, and L/SH Studies as a Function of Primary Maneuver.

Figure 42 shows the percentage of LV driver at-fault incidents in the 100-Car, SB, and L/SH studies as a function of Primary Maneuver. The black bars in Figure 42 represent the LV driver at-fault incidents in the 100-Car Study, while the white and grey bars represent LV driver at-fault incidents in the SB and L/SH studies, respectively. The most frequent Primary Maneuvers for LV driver at-fault incidents in the 100-Car Study were Braking (32.6%), Stopped (21.7%), and Changing Lanes (16.7%). The most frequent Primary Maneuvers for LV driver at-fault incidents in the SB study were Changing Lanes (42.6%), Through Traffic (25.5%), and Roadway Exit (10.6%). The most frequent Primary Maneuvers for LV driver at-fault incidents in the L/SH study were Changing Lanes (26.5%), Left Turn (22.2%), and Through Traffic (13.7%).

Figure 42 . Percentage of LV Driver At-Fault Incidents in the 100-Car, SB, and L/SH Studies as a Function of Primary Maneuver.

Summary of Primary Maneuvers Across Studies

Across the three studies, the most frequent Primary Maneuvers were Changing Lanes (23.2%), Braking (12.3%), and Left Turn (11.2%). These three Primary Maneuvers represented 46.5% of the Primary Maneuvers across the three studies. As can be seen in Figures 40-42, the Primary Maneuvers differed depending on whether the LV or HV was judged to have been at fault.

As can be seen in Figure 41, the most frequent Primary Maneuvers for HV driver at-fault incidents in the 100-Car Study were Changing Lanes (32.9%), Crossing Over the Lane Line (26.3%), and Left Turn (15.2%). These three Primary Maneuvers represented 74.4% of the HV driver at-fault incidents in the 100-Car Study. In the SB study, the most frequent Primary Maneuvers for HV driver at-fault incidents were Through Traffic (71.4%), Changing Lanes (9.5%), and Left Turn (9.5%). These three Primary Maneuvers accounted for 90.4% of the HV driver at-fault incident in the SB study. In the L/SH study, the most frequent Primary Maneuvers for HV driver at-fault incidents were Through Traffic (44%), Right Turn (24%), and Left Turn (12%). These three Primary Maneuvers accounted for 80% of the HV driver at-fault incidents in the L/SH study. From the data it appears that HV drivers had the most difficulties when traveling forward on a roadway or straight through an intersection and changing lanes.

As can be seen in Figure 42, the most frequent Primary Maneuvers for LV driver at-fault incidents in the 100-Car Study were Braking (32.6%), Stopped (21.7%), and Changing Lanes (16.7%). These three Primary Maneuvers accounted for 71% of the LV driver at-fault incidents in the 100-Car Study. In the SB study, the most frequent Primary Maneuvers for LV driver at-fault incidents were Changing Lanes (42.6%), Through Traffic (25.5%), and Roadway Exit (10.6%). These three Primary Maneuvers represented 78.7% of the LV driver at-fault incidents in the SB study. In the L/SH study, the most frequent Primary Maneuvers for LV driver at-fault incidents were Changing Lanes (26.5%), Left Turn (22.2%), and Through Traffic (13.7%). These three Primary Maneuvers accounted for 62.4% of the LV driver at-fault incidents in the L/SH study. From the data it appears that LV drivers had the most difficulties when braking or decelerating and changing lanes.

In the SB study, the Through Traffic (i.e., vehicle traveling forward on a roadway or straight through an intersection) and Changing Lanes Primary Maneuvers accounted for 72% of the total incidents recorded. The Primary Maneuvers associated with LV-HV interactions in the L/SH and 100-Car studies were more varied. Changing Lanes (22.5%), Left Turn (20.4%), Through Traffic (19%), Right Turn (12.7%), and Merge onto Roadway (10.6%) accounted for the majority of incidents recorded in the L/SH study, while Braking (22.8%), Changing Lanes (21.1%), Stopped (15%), and Crossing Over Lane Line (7.7%) represented the majority of Primary Maneuvers in the 100-Car Study. Further investigation of these maneuver types indicated that Through Primary Maneuver was the most frequent type for HVs in both the SB and L/SH studies: 71% and 44%, respectively. However, Changing Lanes (32.9%) was the most predominant Primary Maneuver for HVs in the 100-Car Study.

The Changing Lanes Primary Maneuver was the predominant type for LVs in both the SB and L/SH studies: 42.6% and 26.5%, respectively. However, in the 100-Car Study, the Braking (32.6%) Primary Maneuver was the most predominant type for LVs. Note that the predominant Primary Maneuvers for each group of drivers is consistent with the Incident Type classification presented in the previous section. For example, one would expect that the Primary Maneuver for Late Braking for Stopped/Stopping Traffic would be Through Traffic, which as indicated by the SB at-fault incidents, was the case.

Specific Contributing Factors

Table 42 shows the frequency, percentage, and rank ordering of the Contributing Factors across all three studies. The most frequent Contributing Factor across the three studies was Driving Techniques (41%), followed by Aggressive Driving (24.1%), Unknown (17.1%), and Distracted (10.5%). The reader should bear in mind that more than one Contributing Factor could be selected for a single incident in the 100-Car Study. Figure 43 shows a bar graph of the 456 incidents, across the three studies, as a function of the Contributing Factors.

Table 42. Frequency, Percentage, and Rank Ordering of the Contributing Factors across the 100-Car, SB, and L/SH Studies (n Total = 456).

Figure 43 . Frequency of Contributing Factors across the 100-Car, SB, and L/SH Studies.

Tables 43-45 show the frequency and percentage of each Contributing Factor in the 100-Car, SB, and L/SH studies, respectively. In the 100-Car Study, the most frequent Contributing Factors were Driving Techniques (49.5%), Unknown (24%), Distracted (18.7%), and Aggressive Driving (15%) . In the SB data set, the most frequent Contributing Factors were Driving Techniques (46%) and Aggressive Driving (35%). In the L/SH study, the most frequent Contributing Factors were Aggressive Driving (37%), Driving Techniques (24%), Roadway Alignment (11%), and Unknown (11%). Figure 44 shows a bar graph illustrating the 456 incidents in the 100-Car, SB, and L/SH studies as a function of the Contributing Factors.

Table 43. Frequency and Percentage of Contributing Factors for the 100-Car Study.