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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

 

WHEN SR CRASHES ARE MOST LIKELY TO OCCUR

This section presents tables showing when SR crashes are most likely to occur. It shows the percentage of SR crashes by light condition, road surface, atmospheric condition, season, and day of the week.

 

Light Condition

Surface Condition

Weather

Season

Day of the Week

 

Light Condition

Table 42. Frequency and number/percentage of SR crashes regarding light condition.

Light Condition FARS GES
All Crashes SR Crashes All Crashes SR Crashes
n n Percent n n Percent
Daylight 18,973 4,950 26.09 3,978,106 805,809 20.26
Dark 11,215 4,124 36.77 671,326 168,480 25.10
Dark but lighted 5,564 1,963 35.28 813,033 169,334 20.83
Dawn 710 219 30.85 86,112 20,785 24.14
Dusk 848 263 31.01 131,615 27,809 21.13
Unknown 277 34 12.27 32,548 3,353 10.30
Total 37,587 11,553 30.74 5,712,740 1,195,570 20.93
Note: n represents frequency of crashes.

 

Table 43. Frequency and number/percentage of SR crashes regarding light condition in North Carolina.

Category Over Speed Limit Too Fast for Conditions Total SR Not SR Total
n Percent n Percent n Percent n Percent n Percent
Daylight 6,416 2.34 30,270 11.04 36,686 13.38 237,423 86.62 274,109 100.00
Dark 4,956 5.83 15,348 18.06 20,304 23.89 64,691 76.11 84,995 100.00
Dark but lighted 878 2.95 1,866 6.27 2,744 9.22 27,026 90.78 29,770 100.00
Dawn 254 3.61 1,237 17.57 1,491 21.17 5,551 78.83 7,042 100.00
Dusk 267 2.77 1,115 11.58 1,382 14.35 8,249 85.65 9,631 100.00
Unknown 31 4.63 108 16.12 139 20.75 531 79.25 670 100.00
Total 12,802 3.15 49,944 12.29 62,746 15.45 343,471 84.55 406,217 100.00
Note: n represents frequency of crashes.

 

Table 44. Frequency and number/percentage of SR crashes regarding light condition in Ohio.

Category Over Speed Limit Too Fast for Conditions Total SR Not SR Total
n Percent n Percent n Percent n Percent n Percent
Daylight 16,918 5.78 11,895 4.07 28,813 9.85 263,681 90.15 292,494 100.00
Dark 6,007 8.33 6,875 9.53 12,882 17.86 59,259 82.14 72,141 100.00
Dark but lighted 6,031 10.62 1,207 2.12 7,238 12.74 49,567 87.26 56,805 100.00
Dawn 648 6.79 627 6.57 1,275 13.35 8,273 86.65 9,548 100.00
Dusk 700 6.41 443 4.06 1,143 10.46 9,781 89.54 10,924 100.00
Unknown 373 6.09 182 2.97 555 9.06 5,574 90.94 6,129 100.00
Total 30,677 6.85 21,229 4.74 51,906 11.59 396,135 88.41 448,041 100.00
Note: n represents frequency of crashes.

With minor exceptions, all databases and definitions in table 42 through table 44 indicated that crashes at night had the highest percentage of SR crashes. The findings in the "Dark but lighted" category varied between databases.

 

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Surface Condition

Table 45. Frequency and number/percentage of SR crashes regarding surface condition.

Surface Condition FARS GES
All Crashes SR Crashes All Crashes SR Crashes
n n Percent n n Percent
Dry 31,241 9,196 29.44 4,401,379 774,151 17.59
Wet 4,768 1,627 34.12 866,361 234,023 27.01
Snow or slush 569 299 52.55 209,910 103,822 49.46
Ice 547 317 57.95 153,079 69,146 45.17
Sand, dirt, or oil 48 28 58.33 7,336 2,114 28.82
Other       9,231 3,738 40.49
Unknown       65,444 8,575 13.10
Total 37,587 11,553 30.74 5,712,740 1,195,569 20.93
Note: n represents frequency of crashes.

 

Table 46. Frequency and number/percentage of SR crashes regarding surface condition in North Carolina.

Surface Condition Over Speed Limit Too Fast for Conditions Total SR Not SR Total
n Percent n Percent n Percent n Percent n Percent
Dry 10,791 3.50 15,558 5.04 26,349 8.54 282,322 91.46 308,671 100.00
Wet 1,868 2.38 21,025 26.75 22,893 29.13 55,703 70.87 78,596 100.00
Snow or slush 24 0.30 5,845 73.30 5,869 73.60 2,105 26.40 7,974 100.00
Ice 73 0.73 7,304 73.34 7,377 74.07 2,582 25.93 9,959 100.00
Sand, dirt, oil, or other 20 4.36 170 37.04 190 41.39 269 58.61 459 100.00
Unknown 26 4.66 42 7.53 68 12.19 490 87.81 558 100.00
Total 12,802 3.15 49,944 12.29 62,746 15.45 343,471 84.55 406,217 100.00
Note: n represents frequency of crashes.

 

Table 47. Frequency and number/percentage of SR crashes regarding surface condition in Ohio.

Surface Condition Over Speed Limit Too Fast for Conditions Total SR Not SR Total
n Percent n Percent n Percent n Percent n Percent
Dry 22,418 7.39 4,231 1.40 26,649 8.79 276,565 91.21 303,214 100.00
Wet 6,768 6.66 6,388 6.28 13,156 12.94 88,517 87.06 101,673 100.00
Snow or slush 753 2.91 6,398 24.72 7,151 27.63 18,734 72.37 25,885 100.00
Ice 359 3.22 3,259 29.26 3,618 32.48 7,521 67.52 11,139 100.00
Sand, dirt, oil, or other 211 6.26 900 26.72 1,111 32.99 2,257 67.01 3,368 100.00
Unknown 168 6.08 53 1.92 221 8.00 2,541 92.00 2,762 100.00
Total 30,677 6.85 21,229 4.74 51,906 11.59 396,135 88.41 448,041 100.00
Note: n represents frequency of crashes.

The surface condition variable was the first of two variables (the second being weather) in which the findings from the combined versus over speed limit definitions consistently differed (see table 45 through table 47). The combined definition for all databases indicated higher SR crash percentages for snow and ice conditions. In contrast, the over speed limit definition for both States showed that the dry condition had the highest percentage of SR crashes. This is not unexpected, as an investigating officer may be likely to conclude that most drivers go too fast for conditions even without speeding per se in snowy and icy conditions. One conclusion that might be drawn is that SR crashes in snowy and icy conditions might be better treated by roadway (e.g., snow and ice removal) or vehicles treatments rather than by enforcement or education efforts.

 

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Weather

Table 48. Frequency and number/percentage of SR crashes regarding weather.

Weather FARS GES
All Crashes SR Crashes All Crashes SR Crashes
n n Percent n n Percent
No adverse atmospheric conditions 33,036 9,907 29.99 4,808,369 899,217 18.70
Rain 2,805 992 35.37 547,389 156,006 28.50
Sleet 131 71 54.20 17,339 7,019 40.48
Snow 616 307 49.84 230,049 115,887 50.37
Fog 420 145 34.52 22,127 4,862 21.97
Rain and fog 31 13 41.94 1,819 359 19.74
Sleet and fog 10 7 70.00 503 241 47.91
Other; smog, smoke, blowing sand, snow, dust, crosswind, etc. 184 50 27.17 31,065 6,962 22.41
Unknown 354 61 17.23 54,079 5,017 9.28
Total 37,587 11,553 30.74 5,712,739 1,195,570 20.93
Note: n represents frequency of crashes.

 

Table 49. Frequency and number/percentage of SR crashes regarding weather in North Carolina.

Weather Over Speed Limit Too Fast for Conditions Total SR Not SR Total
n Percent n Percent n Percent n Percent n Percent
No adverse  atmospheric conditions 11,410 3.44 22,922 6.91 34,332 10.34 297,589 89.66 331,921 100.00
Rain 1,164 2.01 17,773 30.67 18,937 32.68 39,003 67.32 57,940 100.00
Sleet 21 0.58 2,528 69.55 2,549 70.12 1,086 29.88 3,635 100.00
Snow 26 0.32 5,636 70.04 5,662 70.36 2,385 29.64 8,047 100.00
Fog 151 4.18 799 22.14 950 26.32 2,659 73.68 3,609 100.00
Rain and fog 11 2.60 170 40.19 181 42.79 242 57.21 423 100.00
Sleet and fog 3 9.68 18 58.06 21 67.74 10 32.26 31 100.00
Other; smoke, dust, or wind 16 2.62 98 16.04 114 18.66 497 81.34 611 100.00
Unknown                    
Total 12,802 3.15 49,944 12.29 62,746 15.45 343,471 84.55 406,217 100.00
Note: n represents frequency of crashes. Blank cells indicate that the code was not present in this database.

 

Table 50. Frequency and number/percentage of SR crashes regarding weather in Ohio.

Weather Over Speed Limit Too Fast for Conditions Total SR Not SR Total
n Percent n Percent n Percent n Percent n Percent
No adverse atmospheric conditions 24,925 7.23 8,027 2.33 32,952 9.56 311,655 90.44 344,607 100.00
Rain 3,691 6.69 3,670 6.65 7,361 13.35 47,794 86.65 55,155 100.00
Sleet                    
Snow 1,285 3.73 7,671 22.28 8,956 26.01 25,480 73.99 34,436 100.00
Fog 259 7.11 281 7.71 540 14.81 3,105 85.19 3,645 100.00
Rain and fog                    
Sleet and fog                    
Other; smoke, dust, or wind 278 4.47 1,489 23.94 1,767 28.41 4,453 71.59 6,220 100.00
Unknown 239 6.01 91 2.29 330 8.30 3,648 91.70 3,978 100.00
Total 30,677 6.85 21,229 4.74 51,906 11.59 396,135 88.41 448,041 100.00
Note: n represents frequency of crashes. Blank cells indicate that the code was not present in this database.

The findings from table 48 through table 50 support those from table 45 through table 47. Using the combined definition of SR (predominantly too fast for conditions), adverse weather conditions had a higher SR crash percentage. Using the over speed limit definition, nonadverse conditions had a higher SR crash percentage.

 

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Season

Table 51. Frequency and number/percentage of SR crashes regarding season.

Season FARS GES
All Crashes SR Crashes All Crashes SR Crashes
n n Percent n n Percent
Winter 8,269 2,540 30.72 1,484,529 355,032 23.92
Spring 9,085 2,813 30.96 1,395,434 278,033 19.92
Summer 10,224 3,153 30.84 1,379,243 275,118 19.95
Fall 10,009 3,047 30.44 1,453,533 287,387 19.77
Total 37,587 11,553 30.74 5,712,739 1,195,570 20.93
Note: n represents frequency of crashes.

 

Table 52. Frequency and number/percentage of SR crashes regarding season in North Carolina.

Season Over Speed Limit Too Fast for Conditions Total SR Not SR Total
n Percent n Percent n Percent n Percent n Percent
Winter 2,684 2.61 19,791 19.24 22,475 21.85 80,405 78.15 102,880 100.00
Spring 3,438 3.57 9,085 9.42 12,523 12.99 83,889 87.01 96,412 100.00
Summer 3,463 3.53 11,077 11.28 14,540 14.80 83,695 85.20 98,235 100.00
Fall 3,217 2.96 9,991 9.19 13,208 12.15 95,482 87.85 108,690 100.00
Total 12,802 3.15 49,944 12.29 62,746 15.45 343,471 84.55 406,217 100.00
Note: n represents frequency of crashes.

 

Table 53. Frequency and number/percentage of SR crashes regarding season in Ohio.

Season Over Speed Limit Too Fast for Conditions Total SR Not SR Total
n Percent n Percent n Percent n Percent n Percent
Winter 7,049 5.78 11,304 9.27 18,353 15.05 103,560 84.95 121,913 100.00
Spring 7,584 7.31 4,101 3.95 11,685 11.26 92,061 88.74 103,746 100.00
Summer 7,803 7.53 2,545 2.46 10,348 9.99 93,233 90.01 103,581 100.00
Fall 8,241 6.94 3,279 2.76 11,520 9.70 107,281 90.30 118,801 100.00
Total 30,677 6.85 21,229 4.74 51,906 11.59 396,135 88.41 448,041 100.00
Note: n represents frequency of crashes.

While GES and FARS data in table 51 showed essentially no differences between seasons for total SR, the State data using the same definition in table 52 and table 53 showed that winter had a higher SR percentage. This could result from the States having more snowy and icy conditions in winter and thus more SR crashes resulting from driving too fast for the condition than the average State represented in FARS and GES. The over speed limit category showed slight differences between seasons.

 

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Day of the Week

Table 54. Frequency and number/percentage of SR crashes regarding day of the week.

Day of the Week FARS GES
All Crashes SR Crashes All Crashes SR Crashes
n n Percent n n Percent
Weekend 12,842 4,492 34.98 1,320,236 289,867 21.96
Weekday 24,735 7,059 28.54 4,392,503 905,703 20.62
Unknown 10 2 20.00 0 0 0.00
Total 37,587 11,553 30.74 5,712,739 1,195,570 20.93
Note: n represents frequency of crashes.

 

Table 55. Frequency and number/percentage of SR crashes regarding day of the week in North Carolina.

Day of the Week Over Speed Limit Too Fast for Conditions Total SR Not SR Total
n Percent n Percent n Percent n Percent n Percent
Weekend 4,583 4.60 14,938 15.00 19,521 19.60 80,097 80.40 99,618 100.00
Weekday 8,219 2.68 35,006 11.42 43,225 14.10 263,374 85.90 306,599 100.00
Total 12,802 3.15 49,944 12.29 62,746 15.45 343,471 84.55 406,217 100.00
Note: n represents frequency of crashes.

 

Table 56. Frequency and number/percentage of SR crashes regarding day of the week in Ohio.

Day of the Week Over Speed Limit Too Fast for Conditions Total SR Not SR Total
n Percent n Percent n Percent n Percent n Percent
Weekend 9,065 8.75 6,728 6.50 15,793 15.25 87,790 84.75 103,583 100.00
Weekday 21,612 6.27 14,501 4.21 36,113 10.48 308,345 89.52 344458 100.00
Total 30,677 6.85 21,229 4.74 51,906 11.59 396,135 88.41 448,041 100.00
Note: n represents frequency of crashes.

As seen in table 54 through table 56, the percentage of SR crashes was highest on the weekends except for GES in which no difference was seen.

 

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FHWA-HRT-10-024

 

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