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Publication Number: FHWA-HRT-10-024
Date:April 2010

Development of a Speeding-Related Crash Typology

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RESULTS FOR SINGLE-VARIABLE ANALYSES

 

ANALYSES OF DATA SUBSETS

Following a review of the above tables, the FHWA requested additional tables on subsets of the data. The request was for specific tables concerning only SR crashes in FARS and GES for five data subsets which included: (1) pedestrian crashes, (2) intersection crashes, (3) lane departure crashes, (4) rural crashes, and (5) urban crashes. Lane departure crashes were defined using a standard FHWA definition including single–vehicle, run–off road crashes; multivehicle, head–on crashes; multivehicle, opposite–direction front–to–side crashes; and multivehicle, opposite–direction sideswipe crashes. Within each subset, tables for only selected variables were requested, as follows:

  • Pedestrian crashes: rural/urban, functional class, day/night (using light condition), speed limit, relationship to junction, number of travel lanes, pedestrian age, and pedestrian alcohol use.

  • Intersection crashes: rural/urban, functional class, day/night, speed limit, traffic control device, number of travel lanes, alignment, grade, driver age, and driver alcohol use.

  • Lane departure crashes: rural/urban, day/night, speed limit, number of travel lanes, alignment, grade, surface condition, driver age, and driver alcohol use. Note that tables were run for all lane departure crashes and then only for the single–vehicle, run–off–road crashes.

  • Rural crashes: lane departure (by category), day/night, speed limit, relationship to junction, alignment, grade, number of travel lanes, surface condition, pedestrian related, driver age, and driver alcohol use.

  • Urban crashes: lane departure (by category), day/night, speed limit, relationship to junction, alignment, grade, number of travel lanes, surface condition, pedestrian related, driver age, and driver alcohol use.

Note that in all cases, the tables related to pedestrian/driver age and alcohol use were vehicle specific, while the remaining tables were crash specific. In addition, the analyses for rural and urban crashes and the tables for rural/urban and functional class could only be run with FARS data because GES did not include these variables.

The following sections present summary results for each data subset. These results differ from the original single–variable results. For the single–variable results, the goal was to define categories within each critical variable that were more likely to be SR when compared to other categories. However, for these five subsets, the data were restricted to SR crashes, and the goal was to examine the nature of these SR crashes within each subset.

 

SR Pedestrian Crashes

SR Intersection Crashes

SR Lane Departure Crashes

SR Crashes in Rural and Urban Areas

 

SR Pedestrian Crashes

Table 87. Characteristics of SR pedestrian crashes.

Variable

Category

FARS (Percent)

GES (Percent)

Urban   75  
Urban principal and minor arterials   38  
Nighttime   62 50
Speed limit (mi/h) £ 25 17 9
30–35 30 33
40–45 22 20
50–55 13 4
60+ 18 12
Midblock   76 59
Number of lanes 2 38 45
4 33 17
Predominant pedestrian age (years) 11–20 11 27
21–30 18 18
31–40 16 22
41–50 16 8
Pedestrian alcohol   8 8
Total frequency   411 2,994
Note: n represents frequency of crashes. Blank cells indicate that the code was not present in this database.

Table 87 summarizes the key findings from the series of FARS and GES analysis runs related to SR pedestrian crashes. Fatal SR pedestrian crashes were predominantly urban in nature and occurred primarily on arterial roadways. Both fatal and total SR pedestrian crashes occurred mostly during the nighttime on roads with 30–45 mi/h speed limits at midblock (nonintersection) locations and on two–lane roads and streets. Predominant pedestrian age categories varied slightly with the GES database, showing a higher percentage of total SR crashes involving drivers who were 11–20 years old. Alcohol use was found in approximately 8 percent of the pedestrians in both databases.

 

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SR Intersection Crashes

As shown in table 88, fatal SR intersection crashes predominantly occurred in urban areas on principal and minor arterials. While approximately half the fatal SR intersection crashes occurred during the daytime and half at nighttime, a much higher percentage (73 percent) of the total SR intersection crashes occurred in the daytime. Both fatal and total SR crashes were more likely to occur on roads with speed limits of 30–45 mi/h. While the fatal SR intersection crashes were almost equally divided among intersections with stop/yield signs, signals, and no control, over half of the total SR intersection crashes occurred at signalized locations. Both databases indicated that most were on straight and level roads and on two–lane roads with GES having a high percentage of unknown variables in both cases. Predominant driver ages were similar, with slightly more 25–30 year olds involved in the fatal SR intersection crashes. Alcohol was found in a much higher proportion of the fatal SR intersection crashes.

Table 88. Characteristics of SR intersection crashes.

Variable

Category

FARS (Percent)

GES (Percent)

Urban   65  
Urban principal and minor arterials   49  
Daytime   45 73
Speed limit (mi/h) £ 25 15 24
30–35 30 33
40–45 30 32
50–55 21 9
60+ 4 1
Traffic control Stop/yield 33 16
Signals 31 55
No control 32 26
Straight (as opposed to curve/unknown)   83 85
Level (as opposed to grades/hills/unknown)   80 43
Number of lanes 2 54 28
4 28 16
Predominant driver age (years) 16–19 15 21
20–25 30 20
26–35 23 17
36–50 19 22
Alcohol   28 6
Total frequency   1,510 383,900
Note: n represents frequency of crashes. Blank cells indicate that the code was not present in this database.

 

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SR Lane Departure Crashes

Table 89. Characteristics of SR lane departure crashes.

Variable

Category

FARS (Percent)

GES (Percent)

Rural   64  
Functional class Rural major collector 18  
Rural local road 16  
Night   58 46
Speed limit (mi/h) £ 25 6 11
30–35 18 17
40–45 21 17
50–55 39 27
60+ 14 15
Straight (as opposed to curve/unknown)   51 55
Level (as opposed to grades/hills/unknown)   64 39
Two lanes No control 71 55
Dry (as opposed to wet, snowy/icy)   80 49
Predominant driver age (years) 16–19 17 24
20–25 26 25
26–35 21 18
36–50 22 19
Alcohol   35 13
Total frequency   7,796 415,631
Note: n represents frequency of crashes. Blank cells indicate that the code was not present in this database.

As shown in table 89, fatal SR lane departure crashes predominantly occurred in rural areas on major collectors and local roads. While there were slight differences, both databases indicated that approximately half the crashes occurred in the daytime and half in the nighttime and that a higher percentage occurred on roads with speed limits of 50–55 mi/h. Both showed a practically equal split between curves and straight roadway sections. While the fatal SR lane departure crashes were more likely on level roads, a higher percentage of the total SR crashes were on grades or hills. Both exhibited the majority of such crashes on two–lane roads. While the fatal SR lane departure crashes were more likely to be on dry roadways, approximately half of the GES total crashes were on wet/snowy/icy roadways. Predominant driver ages were similar, with more 16–19 year olds in the total SR lane departure crashes for GES. Alcohol was found in a much higher proportion of the fatal SR lane departure crashes.

 

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SR Crashes in Rural and Urban Areas

Note that since GES does not include a rural/urban variable, the information in table 90 only concerns fatal SR crashes.

Table 90. Characteristics of fatal SR crashes by area type (rural/urban).

Variable

Category

FARS (Percent)

GES (Percent)

Single–vehicle run–off–road   68 51
Predominant number of lanes 2 77 42
4 16 28
Dark   48 59
Speed limit (mi/h) £ 25 4 14
30–35 10 28
40–45 18 26
50–55 45 16
60+ 23 15
Not related to junction   89 69
Curves   46 30
Grades/hills   37 23
Dry (as opposed to wet, snowy/icy)   77 83
Pedestrian involved   1 7
Predominant driver age (years) 16–19 16 16
20–25 23 29
26–35 20 24
36–50 24 20
Alcohol   31 30
Total frequency   6,679 4,592
Note: n represents frequency of crashes.

As would be expected, there were differences between the characteristics of rural and urban SR fatal crashes. The rural SR fatal crashes were more likely to be single–vehicle, run–off–road crashes as opposed to multivehicle crashes, and they were more likely to be on two–lane roads at night. Almost half of the rural SR fatal crashes were on roads with 50–55 mi/h speed limits, while the urban SR fatal crashes were at lower speed limits, as expected. Both rural and urban crashes were more likely to be nonintersection crashes on straight level roadways that were not characterized by wet or other slippery conditions. Pedestrian involvement was low for both, but it was much higher in urban areas. There was little difference between driver age or alcohol use.

 

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FHWA-HRT-10-024

 

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