Analysis of Weekday, Weekend, and Holiday Accident Frequencies

Transcription

1 Transportation Kentucky Transportation Center Research Report University of Kentucky Year 198 Analysis of Weekday, Weekend, and Holiday Accident Frequencies Jerry G. Pigman Rolands L. Rizenbergs Donald R. Herd Kentucky Department of Transportation, Kentucky Department of Transportation Kentucky Department of Transportation This paper is posted at UKnoledge. researchreports/787

2 Research Report 546 ANAlYSIS OF WEEKDAY, WEEKEND, AND HOLIDAY ACCIDENT FREQUENCIES by Jerry G. Pigman Research Engineer Chief Rolands l. Rizenbergs Assistant Director and Donald R. Herd Formerly Research Engineer Division of Research Bureau of Highays DEPARTMENT OF TRANSPORTATION Commonealth of Kentucky offered for publication to the Traffic Quarterly March 198

3 ANALYSIS OF WEEKDAY, WEEKEND, AND HOLIDAY ACCIDENT FREQUENCIES by J. G. Pigman, R. l. Rizenbergs, and D. R. Herd ABSTRACT Trends in recent years have indicated that a significant percentage of eekend traffic is recreational and that the proportion of eekend trips is increasing. The "energy crisis" in late 1973, and the associated reduction in speed limit on March 1, 1974, affected eekend travel. A previous study by the Division of Research revealed that significant reductions in the number and rates of highay accidents, fatalitites, and injuries coincided ith the period of time generally referred to as the "energy crisis". loer speeds ere considered to be a primary factor in the reduction of accidents. An alteration in eekend and holiday trips as suspected of contributing to the reduction of accident rates; hoever, information as lacking from hich to make this determination. A comparison of accidents during eekday, eekend, and holiday periods as made; most of the data ere for rural sections of to-lane rads, four-lane roads, interstate routes, and toll roads. On rural roads, the largest number of accidents have occurred on Saturdays, Fridays, and Sundays. Tuesdays generally had the loest number of accidents. Fatal accidents on to-lane roads occurred in similar random patterns of distribution during the eek. The highest rates for to-lane roads ere on Sundays and Saturdays, and the rates for expressays (interstates and toll roads) ere the highest on Sundays. Fatality rates ere distributed similarly to the rates of all accidents. The percentage of accidents on eekends decreased steadily from 35 in 1973 to 32 in likeise, the percentage of fatalities on eekends shoed gradual decreases. Accident rates on eekends ere substantially higher than on eekdays. Rates of fatal and an accidents ere loer during holiday periods than during eekends not involving holidays. Holiday periods had feer accidents per day than eekends but had more accidents per day than eekdays. Traffic volumes, hoever, ere significantly greater during holidays than on either eekends or eekdays.

4 INTRODUCTION Much of eekend traffic is non-business and recreational, and trends indicated that the number of these trips are increasing. The "energy crisis" in late 1973, and the reduction in speed limit on March 1, 1974, hoever, affected eekend travel. Significant reductions in the number and rates of highay accidents, fatalities, and injuries coincided ith the period of time that is- generally referred to as the "energy crisis" (1). Sloer speeds ere considered to be a primary factor in the reduction of accidents. A significant change in eekend and holiday trips as suspected as contributing to the reduction of accident rates; hoever, information as lacking from hich to make this determination. The purpose of this study as to analyze and summarize accident statistics for eekday, eekend, and holiday periods. PROCEDURE Accidents on eekdays, eekends, and holidays ere analyzed by summarizing number of accidents, number of fatalities, accident rates, and fatal accident rates. Rates ere expressed as accidents per 1 million vehicle-miles (MVM)(16 million vehicle-kilometers) of travel. The analysis focused primarily on data for 1973, 1974, and 1975, but 1976 data ere also used. It as necessary to compute accident rates for the rural highay system and its three major components: 1. to-lane (including three-lane) roads, 2. four-lane roads, and 3. expressays (interstates and parkays (toll roads)). Accident rates ere computed for day of the eek and month. A separate file as available for each of the years of study. Since implementation of uniform accident reporting in July 1975 in Kentucky, the number of accidents reported has increased from approximately 3, to 14, per year. The data base, of course, is different. The increased portion of accidents reported since July 1975 come from local jurisdictions. The largest number of accidents come from the five urban counties in the state. To insure that only rural accidents ere included, those occurring in the mostly urban counties ere omitted. Accidents investigated by Kentucky State Police ere the primary data base for the analysis; hoever, all accidents reported in 1976 ere presented, in some cases, for comparison. Accidents ere summarized by severity (fatal, injury, and property damage only) for each day of eek, month, year, and type of road. Computation of vehicle-miles (vehicle-kilometers) of travel on each type of road by

5 day of eek and month presented problems because data ere not available in the desired form. Hoever, in a previous study (2), monthly volumes of travel for a three-year period ( ) had been determined. Adjustment factors ere calculated and applied to convert monthly volumes to daily volumes. Traffic count summaries from 44 automatic traffic recorder stations (28 on to-lane roads, 5 on four-lane roads, and 11 on expressays) ere analyzed. The month-to-day factors ere computed as follos: 1. All data from automatic counters, located on each type of road, ere grouped together. 2. The data from each group (type of road) ere summed by day of eek for each month and eek. Weekly totals ere combined to obtain the monthly totals. 3. The sum for each day of eek as divided by the monthly total to yield day-of-eek factors. 4. The day-of-eek factor multiplied by the monthly volume of travel for the particular year yielded a daily volume of travel. Total accident and fatality rates ere computed for eaclt day of eek, month, year, and for each type of road. Saturday and Sunday values ere combined to calculate eekend accident rates, and Monday through Friday values ere combined to calculate eekday rates. A separate analysis as made for holidays during the study periods. Holidays ere Ne Year's Day, Easter, Memorial Day, Independence Day, Labor Day, Thanksgiving, and. Christmas. The number of days included in each holiday period ere those observed by state government in Kentucky. The entire 24-hour period as included for every day of the holiday period. A factor as developed to represent the percentage of the montly volume in each holiday. This factor as multiplied by vehicle-miles (vehicle-kilometers) of travel during the month of the holiday to obtain travel during the holiday. Accident rates ere calculated from vehicle-miles (vehicle-kilometers) of travel and number of accidents for respective holidays. It as also necessary to separate accidents and travel during holidays from the eekday and eekend accidents and travel. This as done to insure that only applicable data ere used to calculate accident rates for eekdays, eekends, and holidays. Again, adjustment 2

6 factors ere developed for holiday periods by using volumes from automatic traffic recorder sites for 1973 through RESULTS Number of Accidents Number of accidents by day of the eek, year, and highay system are plotted in Figures 1 through 4. Number and percentage of accidents for each day of the eek are shon in Table 1. The largest number of accidents occurred on Saturdays, Fridays, and Sundays, respectively. Tuesdays generally had the loest number of accidents. The "energy crisis", and the associated reduction in speed limit on March 1, 1974, substantially reduced the number of accidents as compared to Accidents increased in 1975 to the 1973 levels. Accidents during 1976 ere even higher for each day of the eek (Figure 4). A summary of 1976 stateide accidents (Table 1) shoed a eekly distribution considerably different from that of accidents reported by State Police in rural areas. On a stateide basis, Fridays had the highest percentage of eekly accidents; this as folloed by Saturdays and Mondays. The emergence on Fridays and Mondays as days having high percentages of accidents may be explained by the fact that 55 percent of accidents reported in 1976 ere in urban areas. The higher volumes associated ith urban traffic during eekdays and Saturdays and the accompanying congestion could contribute to a larger percentage of accidents on eekdays and Saturdays and a smaller percentage on Sundays, hen traffic is light. Saturdays in urban areas are unique because of high traffic volumes related to shopping. The distribution of accidents by eekday and eekend periods for 1973 through 1976 is presented in Table 2. Percentages of accidents occurring on eekends have steadily decreased from 34.6 percent in 1973 to 31.8 percent in A trend in decreasing percentage of accidents during the eekends may be taking place on rural roads, except expressays. Accidents experienced on expressays decreased beteen 1973 and 1974 but increased beteen 1974 and Also, a larger percentage of accidents ere occurring on expressays compared to other roads during the eekends in 1973 and

7 Number of Fatal Accidents A summary of fatal accidents by eekday and eekend periods is presented in Table 3. A plot of number of fatal accidents by day of eek for to-lane roads is presented in Figure 5. The distributions of accidents ere generally the same for fatal accidents as for all accidents (Figure 1 ). Hoever, on four-lane roads and expressays, there ere no patterns. Variation in the data may be attributed to a limited data base. The general trend in percentage of fatal accidents on eekends also shos a gradual decrease in the period from 1973 to This decrease coincided ith the large decrease in total number of accidents during the same period. Accident Rates Accident rates, rather than numbers of accidents, have been accepted as the primary means of comparing and vieing accident levels. Accident rates by day of eek for each type of road are p~esented in Figures 6 through 9. Saturdays and Sundays ere days ith the highest accident rates for to-lane roads. For four-lane roads, no particular trends ere discerned. Accident rates for expressays indicated reduced levels during the middle of the eek if 1974 ''energy crisis" data ere ignored. Distributions of eekday and eekend accident rates for various roads are summarized in Table 4. Weekend accident rates decreased beteen 1973 and 1974 and then increased in 1975 to near the 1973 levels. This again represents the effects of the "energy crisis" and the associated reduction in speed limit. Each year the eekend accident rates ere higher than eekday rates for all roads except four-lane roads. Apparently eekend rates ere not affected to any greater extent than eekday rates by the "energy crisis". A summary of eekday and eekend travel is presented in Table 5. Even though total travel on eekends as approximately the same in 1973 and 1974, and then increased in 1975, the ratio of eekday to eekend travel as generally the same for those periods. Seasonal variations in accident rates are presented in Figure 1. The seasons ere designated as follos: Spring - March, April, May Summer - June, July, August Fall - September, October, November Winter - December, January, February Significant differences in accident rates ere found among seasons of the year. Seasons 4

8 ith highest accident rates ere fall and inter, folloed by spring and summer. Days of the eek ith the highest accident rates in each season ere Saturdays and Sundays, folloed by Fridays. Sundays exhibited especially large differences in accident rates throughout the seasons. Fatal Accident Rates Fatality rates by day of eek for rural roads are presented in Figure 11. The trends are similar to rates of all accidents. Saturdays and Sundays again had the highest rates, folloed by Friday. This pattern as generally the same each year, but the magnitudes of the rates ere considerably different. In 1973, rates ere higher every day of the eek than they ere in 1974 or The distributions of fatality rates by eekdays and eekends are summarized in Table 6. The data sho that rates for each,type of road ere highest in 1973 and generally the same in 1974 and The large reduction in 1974 and since must be attributed primarily to the loer speed limit in effect since March I, Holiday Accident Rates Safety officials have placed a great deal of emphasis on the dangers associated ith driving.. on holidays. Accident rates for the years 1973 through 1975 ere calculated for several holidays; and the results are presented in Tables 7, 8, and 9. From these tables, it as noted that Christmas and Memorial Day had the highest accident rates in 1973 and 1975, but Ne Year's and Thanksgiving had the highest rates in In an attempt to determine if accident rates ere related to volume of travel, average daily vehicle-miles (vehicle-kilometers) of travel ere determined for each holiday during a three-year period. No relationship as found beteen accident rates on holidays and daily vehicle-miles (vehicle-kilometers) of travel. The most significant results from the study are presented in Table 1. A comparison of accident rates for eekday, eekend, and holiday periods revealed that rates for eekdays ere substantially loer than for eekends and that holiday rates ere loer than eekend rates. Also shon in Table 1 is a comparison of fatal accident rates for a three-year period. Fatal accident rates ere also loest on eekdays, and hoi iday rates ere loer than eekend rates. There as an exception in 1975 hen holiday rates of fatal accidents ere higher than eekend rates. Again, travel for the various time periods as determined and the results are presented in Table 11. Daily vehicle-miles 5

9 (vehicle-kilometers) of travel ere highest on holidays every year. Travel on holidays as about 17-percent higher than on eekends not involving holidays; yet, accident rates ere loer (4 to 12 percent) duril'lg holidays. Occurrences of numbers of accidents per days for the various periods are cited in Table 12. Here too, the loest number of accidents are shon to occur during eekdays and the highest during eekends. Accidents on holidays ere more numerous than on eekdays, but the differences ere not large. SUMMARY AND CONCLUSIONS Most accidents in Kentucky occurred on Saturdays, Fridays, and Sundays. Tuesdays generally had the least accidents. Distribution patterns of fatal accidents on to-lane roads ere similar to those for all accidents. The highest rates for to-lane roads ere on Sundays and Saturdays; the highest rates for expressays ere on Sundays. No particular pattern in accident rates could be discerned for four-lane roads. Otherise, the distribution of fatal accident rates as similar to that of accidents. The percentage of accidents occurring on eekends compared to eekdays has steadily decreased from 34.6 percent in 1973 to 31.8 percent in A trend in decreasing percentage of accidents during the eekends may be taking place on all rural roads, except on the expressays. Likeise, the percentage of fatal accidents on eel<ends also shoed gradual decreases from 1973 to 1975, Each year, accident rates on eekends ere substantially higher than on eekdays for to-lane roads and expressays. The number of accidents per day during eekends as substantially higher than during eekdays. Emphasis on enforcement of traffic las during eekends, therefore, may be justifiable since both the number and rate of accidents are the highest then. Rates of fatal and all accidents ere found to be loer during holiday periods than during eekends not involving holidays, but higher than during eekdays, Holiday periods had substantially feer numbers of accidents per day than eekends and somehat larger numbers of accidents per day than eekdays. Daily volumes of traffic on holidays, hoever, as significantly greater than on either eekends or eekdays. Apparently, attempts to arn the driving public of hazards associated ith highay 'l!tavel during holiday periods, and increased efforts by the police to patrol highays, have had some impact in reducing accidents. 6

10 Significant differ~nces in accident rates on rural roads occurred beteen seasons of the year. The highest rates ere in fall and inter, and the loest ere in spring and summer. Sundays had the highest rates every season of the year. The first year of reporting ~tateide accidents in Kentucky as On a stateide basis, Fridays emerged as the day on hich the highest percentage of eekday accidents occurred, folloed by Sundays and then Mondays. About 55-percent of the accidents in 1976 ere in urban areas. Higher volumes of urban traffic during eekdays and Saturdays ould contribute to higher percentages of accidents. Both the number of accidents and accident rates decreased in 1974 from the 1973 levels. This decrease as associated ith the "energy crisis" and the accompanying reduction in speed limit in March The number of accidents increased in 1975 to about the 1973 levels, but accident rates remained somehat loer. Fatality rates in 1975 remained at much loer rates than in REFERENCES 1. Agent, K. R.; Herd, D. R.; and Rizenbergs, R. L.; First Year Effects of the Energy Crisis on Rural Highays in Kentucky, Record 567, Transportation Research Board, Agent, 1<. R.; and Deen, R. C.; Relationships beteen Roaday Geometries and Accidents, Record 541, Transportation Research Board,

11 TAI3LE1. NUIVIBER AND PERCENT OF ACCIDENTS BY DAY OF WE;EI< (STATE-POLICE REPORTED ACCIDEi\ITS IN RURAL AREAS) DAY OF WEEK SUNDAY MONDAY TUESDAY WEDNESDAY THURSDAY FRIDAY SATURDAY TOTAL NUMBER PERCENT NUMBER PERCE~T NUMBER PERCENT NUMBER PERCENT 4, 327 l5o4 3t o4: ' ~7 3. t) ' a 4 ~ 1 3 tl l3 D 1 3d ), 4d ll.9 3, 8 R o432 l2o2 ), Q';l ) I o , , soz 13 o a oz , o'-t o t , CIZZ 17.7 s , ,145 1.o 28,292 1.o o 197(:;,:: \lumber PERCE~T D 1 19, , , l3.6 25t ,83 16~4 138~711 1.o *INCLUDES ALL ACCIDENTS RfPQRTEO IN 1476 TAtlLE 2. OISTRitlUTIOI\1 OF WEEKDAY AI\JD WEEKEND ACCI DENTS i3y TYPE OF ROAD WEEKDAY WEEKEND YEAR ROAD NUMBER PERCENT NUMP ER PERCENT TWO-LANE 15,875 65~4 8' FOUR-LANE EXPRESSWAY 1, ALL 18, , TWO-LANE 14, ' FOUR-LANE l EXPRESSWAY 1, ALL 16, , TWO-LANE 17, , FOUR-lANE EXPRESSWAY 1, ALL 19, , ALL 21' , ~' ALL 1, ' *INCLUDES ALl ACCIDENTS REPORTED IN

12 TABLE 3. DISTRIBUTION OF WEEKDAY AI\ID WEEKEi\ID FATAL ACCiiJENTS BY TYPE OF ROAD WEEKDAY WEEKEND YEAR ROAD NW'IBER PERCENT NUMBER PERCENT TWO-LANE ol FOUR-LANE l EXPRESSWAY :n.o ALL TWO-LANE FOUR-LANE EXPRESSWAY 26 63o ALL TWO-LANE FOUR-LANE EXPRESSWAY ALL TABLE 4. DISTRIBUTIOI\1 OF VVEEKUAY AI\ID WEEI<Ei\ID ACCI DENT RATES i3y TYPE UF RO.'\D ACCIDENTS/lOG MVM YEAR ROAD WEEKDAY WEEKED - TWO-LANE FOUR-LANE EXPRESSWAY ALL Zll 253 TWO-LANE FOUR-LANE EXPRESSWAY All 184 Zl6 TWO-LANE FOUR-LANE EXPRESSWAY 6 74 ALL

13 TAI3LE 5. WEEKDAY AND WEEKEND D ISTR IBUTIOi\1 OF TRAVEL WEEKDAY WEE KENO TOTAl YEAR ROAD TRAVEL PERCENT TRAVEL PERCENT TRAVEL TWO-LANE 6,292'' 7. 2' , FOUR-LANE EXPRESSWAY l' o9 2,84 ALL , ,585 TWO-LANE ' , FOUR-lANE EXPRESSWAY lt848 ' o 2,719 ALL 8, o ,456 TWO-LANE 6, z a. 6 9, FOUR-LANE EXPRESSWAY l' o92 All o 3o l3' 2 56 *MILLION VEHICLE-MILES (1,6 MILLION VEHICLE-K!LOMETERSI TA!3LE 6. ijistridution OF WEEKDAY AND WEEKEND FATAL ACCIDEI\IT RATES BY TYPE OF ROAD FATAL ACCIDENTS/lOOMVM YEAR ROAD WEEKDAY WEEKEND 1913 TWO-LANE 6o4 9.5 FOUR-LANE 3.9 6o6 EXPRESSWAY AU TWO-LANE FOUR-LANE EXPRESSWAY lo4 1,.1 All 4ol TWO-LANE FOUR-LANE 2.9 Oo9 EXPRESSWAY lo3 2.4 All 4o2 5o3 1

14 TABLE 7. HOLIDAY ACCIDENT RATES NEW YEAR'S!DECEMBER 3-31, 1972 ACCIDENTS /1 MVM TWO-LANE FOUR-LANE EXPRESSWAYS ALL TOTAL FATAL TOTAL FATAL TOTAL FATAL TOTAL FATAl JANUARY t < EASTER!APRIL 2! , MEMORIAL DAY I MAY CJ5e INDEPENDENCE DAY!JULY , e !8 8.1 LABOR DAY I SEPTEMBER THANKSGIVING I NOVEMBER L 2., CHRISTMAS!DECEMBER , TOTAL 1'22 DAYS I TABLE 8. HOLIDAY ACCIDENT RATES NEW YEAR'S!DECEMBER 29-3!, 1973 ACCIDENTS/1 MVM TWO-LANE FOUR-LANE EXPRESSWAYS ALL TOTAL FATAL TOTAL FATAL TOTAL FATAL TOTAL FATAL JANUARY 1, o. 5 EASTER (APRIL! ? MEMORIAL DAY!MAY t INDEPENDENCE DAY!JULY labor DAY!AUGUST 31 SEPTEMBER l-2 I THANKSGIVING!NOVEMBER 28-3 DECEMBER u 3! 6.! CHRISTMAS!DECEMBER ], TOTAl 122 DAVSI ZH &7 o.s 23 " " 11

15 TABLE 9. HOLIDAY ACCIDENT RATES 1975 ACCIDENTS/tOO MVM TWO- LANE FOUR-LANE EXPRESSWAYS ALL TOTAL FATAL TOTAL FATAL TOTAL FATAL TOTAL NEW YEAR'S ~DECEMBER 31, 1974 JANUARY 1' 197 5) ~ EASTER I MARCH 29-3 I MEMORIAL DAY I MAY INDEPENDENCE DAY IJULY LABOR DAY (AUGUST 3-31, SEPTEMBER THANKSGIVING I NOVEMBER 27-3) CHRISTMAS I DECEMBER TOTAL 122 DAYSI FATAL o TABLE 1. A COMPARISON OF WEEKDAY, WEEKEND, Ar\ID HOLI DAY ACCIDENT RATES ACCIDENTS/1 MVM TOTAL FATAL TOTAL FA TAL TOTAL FATAL WEEKDAYS WEEKENDS HOLIDAYS

16 TABLE 11. COMPARISON OF WEEKDAY, WEEKEND, Ai\ID HOLI DAY TRAVEL MVM/DAY WEEKDAYS WEEKENDS HOLIDAYS o TABLE 12. COMPARISON OF ACCIDENTS PER DAY ON WEEKDAYS, WEEKENDS, AND HOLIDAYS ACCIDENTS/DAY WEEKDAYS WEEKENDS'-' HOLIDAYS *INCLUDES HOLIDAY WEEKENDS 13

17 5, CJl >- 2 u.j Cl u t.l <( "- a: 4, 3, ::;; z , I,_,,,L_ SUN MON TUE WED THU FRI DAY OF WEEK SAT Figure 1. i\lumi.jer of Accidents versus Day of Week; To-Lane Roads. 24 CJl >- 2 u u <( "" ro :; z SUN MON TUE WED THU FRI DAY OF WEEK SAT Figure 2. Number of Accidents versus Day of Week; Four-Lane Roads. 14

18 ,_ 425 z c (3 <.l ~ :: :!: 325 :l 275 z SUN MON TUE WEO THU FRI SAT DAY OF WEEK Figure 3. Number of Accidents versus Day of Week; Expressays. 6, ,,_ "" ;;;: (3 ~ Lb a:: :!: :l z 5, 4, 3, ~ SUN MON TUE WED THU FRI SAT DAY OF WEEK Figure 4. Number of Accidents versus Day of Week; To-lane and Four-Lane Roads and Expressays. 15

19 16 14 "" 2 LIJ Q ;:; <: 12.J 1 <: ~ u. Ll. 8 6 ::!! ::> " 4 2 SUN Figure 5. MON TUE WED THU FRI SAT DAY OF WEEK Number of Fatal Accidents versus Day of Week; To-lane Roads. "" ' :;; llj 35 :;; '" ;;;..J!:1..J ".J!::1 > ~ z '" ::; z > "" -' Q 2 :;;..J Q -' u :;; u ~ <( :: " 3 ~. F !I) F- SUN <( LIJ (3 (J <( MON TUE WED THU FRI DAY OF WEEK SAT Figure 6. Accident Rate versus Day of Week; To-lane Roads. Hi

20 2 a: > ' ::< ::< '..J " J: -' " > J: 15 >- 2 <( > a: Q -' J Q 2 ::< -'...J u ::< u ~ <( : :. ~ Cl)... 2 u 1 u u 5 <( 1975 <( SUN MON TUE WED THU FRI SAT DAY OF WEEK Figure 7. Accident Rate versus Day of Weel<; Four-Lane Roads. C/) a: Cl) 1-...J ::< :;:...J :; " J J:..J... 2 " > J: 1 <( > a;; Q -' 2 >-..J 2 ::< :;..J :;: u u ~ <( a: 5. ~ a: Cl) 1- c::; z u u <( <( SUN MON TUE WED THU FRI SAT DAY OF WEE I< Figure 8. Accident Rate versus Day of Week; Expressays. 17

21 a: 3 1-.J ::;; ::;; -' -' ;;:;!::1 :r:.j >!:: z :r:..: a: g >....J -' z z ::;;.J.J S! f.) :;; f.) <( - :: F '"... - z 1- f.) z f.)..: S! 2 f.) f.) 15 < SUN MON TUE WED THU FRI SAT DAY F WEEK ' Figure 9. Accident Rate versus Day of Week; To-lane and Four-lane Roads and Expressays. (I) : WI =:;; : g '" -' S! J: _, U >;: >- <( Z> " :::12 >- -> z ~:i _, 3 25 '' g:; u <( - :~ 2 "-a: '" >-"" '">- Oz c::; UCl..:c::; u <( Figure 1. SPRING '-- SUN MON TUE WED THU FRI SAT DAY OF WEEK Accident Rate versus Day of Week by Seasons of the Year ( ); To-lane and Four-lane Roads and Expressays. 18

22 a:: 9 f-..j :;: :;: -' ;;; -'!:1 7 J:...J f- (.) <! : > J: z f- > z..j z "...J Q (.) :;:...J 5 (.) -' <! :;: -' ~ <! f- : ~ <!. "- : 3 f-.. z LU " u z f- LU (.) <! " u (.) <! SUN MON TUE WED THU FRI DAY OF WEEK SAT Figure 11. Fatal Accident Rate versus Day of Week; To-Lane and Four-Lane Roads and Expressays. 19