JSAE Review 21 (2000) 103}108

Accident analysis of sports utility vehicles: human factorsfrom statistical analysis and case studies

Nobuaki Takubo!, Koji Mizuno"

!National Research Institute of Police Science, Kashiwanoha 6-3-1, Kashiwa-shi, Chiba, 277-0882 Japan"Trazc Safety and Nuisance Research Institute, Shinkawa 6-38-1, Mitaka-shi, Tokyo, 181-0004 Japan

Received 30 April 1999

Abstract

Recently, with leisure time increasing in Japan, Sports Utility Vehicles (SUVs) have become very popular. Therefore, accidentsinvolving SUVs are also increasing. We analyze SUV accidents using statistics and the case study method accessing a nationalaccident database and in-depth accident investigative data. SUV accidents may be characterized by accident type, driver age, purposeof travel, injured occupant age, collision type, etc. Among the case studies, one accident involving pedestrians, one rear-end collision,and one rollover are analyzed. Accident factors, especially human factors, are discussed. ( 2000 Society of Automotive Engineers ofJapan, Inc. and Elsevier Science B.V. All rights reserved.

1. Introduction

In the present tra$c situation, not only the increase inthe number of the accidents and injuries, but also thevariety of the accidents with an increase in nighttime, andelderly driver accidents, are recognized as important.This variety is partly due to changes in the social activ-ities of people. Particularly, as leisure activities such ascar travel are becoming more popular, it is necessary toinvestigate tra$c accidents in relation to leisure time. InJapan, many drivers use Sports Utility Vehicles (SUVs),and registrations are increasing. Therefore, in the currentstudy, the authors focus on accidents involving this typeof vehicle. Macro (statistical) analysis using police data,and microanalysis using in-depth accident data wereperformed in order to develop a strategy to prevent SUVaccidents.

In the present study, SUV accidents are investigated,and one-box vehicles which are used in a similar way toSUVs are also examined. In order to compare signi"cantaccident factors, accidents involving sedans (engine dis-placement of less than 2.0 l) are analyzed.

2. Methodology

The following methods are used to investigate SUVaccidents [1]:

I. Macro data analysis (statistic analysis): Using the acci-dent data in Japan, the characteristics of SUV accidents areclari"ed by comparing them with those of one-box vehiclesand sedans. The analyses focus on: accident types, purposesof travel, impact sites of the vehicles, and driver ages.

II. Micro data analysis (in-depth accident analysis):The obvious features of SUVs in certain accident con"g-urations are examined, and the situations and back-grounds of the accidents are clari"ed.

3. Macro data analyses of SUV accidents

The accidents of three vehicle categories such as SUV,one-box (mini van) and sedan are compared. The totalaccident data in 1993}1995 are examined. As the numberof accidents is still not su$cient to analyze in detail,statistical signi"cance is not examined.

Fig. 1 shows the trend in the ratio of accident numbersof each vehicle category from 1992 to 1995. The number ofSUV accidents shows the most rapid increase comparedwith other vehicle groups. It is considered that this trend isdue to the increase in the registration numbers of SUVs.

3.1. Accident type (accident conxguration)

The accident data are analyzed by road-user typesof victims and accident occurrences. The accidents are

0389-4304/00/$20.00 ( 2000 Society of Automotive Engineers of Japan, Inc. and Elsevier Science B.V. All rights reserved.PII: S 0 3 8 9 - 4 3 0 4 ( 9 9 ) 0 0 0 5 7 - 0 JSAE20004001

Fig. 1. Trend of accidents by vehicle type (Baseline is the number ofaccidents in 1992)

Fig. 2. Accident types for SUVs, one-box vehicles and sedans.

Fig. 3. Accident types by vehicle among pedestrian accidents.

classi"ed into those involving SUVs, one-box vehiclesand sedans, where the drivers in these vehicle types bearinitial responsibility for the accidents. Fig. 2 shows thedistributions of pedestrian-vehicle, multi-vehicle andsingle-vehicle accidents.

In all vehicle groups, more than 80% of the accidentsare multi-vehicle accidents. For SUVs, 88% are multi-vehicle accidents, and 9% are pedestrian accidents. Thisdistribution tendency is similar to that of sedans. How-ever, 84% of one-box vehicle accidents are multi-vehicleaccidents, and 12% are pedestrian accidents, whichshows that the rate of pedestrian accidents for one-boxvehicles is higher than for other vehicle types.

3.1.1. Vehicle-pedestrian accidentsThe car pedestrian accidents are examined by types of

pedestrian behavior before the accidents, such as road-side walking, crossing, road works and others (Fig. 3).Although pedestrian crossings account for the largestproportion for all types of vehicles, the percentage forSUVs is 65%, which is lower than for other vehicleclasses (70%). The tendency of pedestrian behavior in theSUV accidents di!ers from that for one-box vehicles andsedans.

3.1.2. Multi-vehicle collisionsIn multi-vehicle collisions, 39% of SUVs, are involved

in rear-end collisions, a percentage higher than for one-box vehicles (31%) and sedans (33%). For SUVs, 27%are intersection collisions (crossing collisions). This per-centage is lower than for one-box vehicles (31%) andsedans (33%) (Fig. 4).

3.1.3. Single-vehicle accidentsIn single-vehicle accidents, the proportion of crashes

into "xed objects is the highest: 62% for SUVs, 67% forone-box vehicles and 75% for sedans. SUVs and one-boxvehicles are more likely to be involved in running o! theroad and rollover accidents, 24 and 19% in single-vehicle

accidents, respectively, which are higher than that forsedans (15%). Rollover accidents account for 5% forSUVs, 3% for one-box vehicles and 1% for sedans. Theproportion of crashes into a parked vehicle is high forone-box vehicles (Fig. 5).

3.2. Driver characteristics

3.2.1. Driver ageThe age distributions of the drivers involved in the

accidents are discussed (Fig. 6). The proportion of driverages for sedans is similar to SUVs, except for the 20}24age group which was slightly higher, whereas SUVdrivers aged 29 or less account for as large a proportion

104 N. Takubo, K. Mizuno / JSAE Review 21 (2000) 103}108

Fig. 4. Accident types in multi-vehicle accidents.

Fig. 5. Accident types in single-vehicle accidents.

Fig. 6. Driver age in vehicle types.

Fig. 7. Vehicle direction in pedestrian crossing accidents.

as 60%. One-box vehicle accidents distribute over a wideage range, with drivers aged 35}49 constituting the high-est proportion.

3.2.2. Purpose of travelWhen the purposes of travel of the drivers involved in

accidents are examined, private business accounts for thelargest proportion: 82% for the SUVs, 75% for one-boxvehicles, 77% for sedans. The percentage of business usefor SUVs is 2%, which is lower than for other vehiclecategories (6%).

3.3. Characteristics of pedestrian accidents

3.3.1. Pedestrian road-crossing accidentsVehicle-pedestrian accidents occur most frequently

when the pedestrians are crossing the road. Fig. 7 shows

the vehicle travelling directions in this type of accident.The proportion of accidents while the vehicle was turningright is high for SUVs (31%) and one-box vehicles (39%).For SUVs, about 56% of pedestrian road-crossingaccidents occur while the vehicle is traveling forward,which is lower than the 72% for one-box vehicles andsedans.

3.3.2. Vehicle impact sites in pedestrian accidentsThe impact sites of the vehicle are classi"ed into eight

locations. Fig. 8 shows their distributions. In all vehiclegroups, the proportions of front impacts are the highestat about 36}39%. For SUVs, the proportions of rear(9%), right-rear (2%) and left-rear (2%) impacts are high-er than for other vehicle types, while those of front andleft-front are lower. The sedan has a high proportion ofimpacts on the left (10%).

N. Takubo, K. Mizuno / JSAE Review 21 (2000) 103}108 105

Fig. 9. Age of pedestrians injured in accidents.

Fig. 8. Impact sites of vehicle in pedestrian accidents.

Fig. 10. Accident site (Case 1).

3.3.3. Pedestrian ageFig. 9 shows the distribution of the age of pedestrians

involved in accidents by three types of vehicles. Whenstruck by a sedan, 33% of the pedestrians are aged 15 orless, and this proportion is higher than for other types ofvehicles (29%). In fatal accidents, the proportion of pe-destrians aged 15 or less is 11% for SUVs and 7% forone-box vehicles, which is higher than that for sedans(3%). Pedestrians aged 65 or more account for higherproportions (53% for the SUVs and one-box, and 56%for sedan) than other age groups fatally injured by thesame vehicle types.

4. Micro data analysis of SUV accidents

Based on the results of the macrodata analysis, someaccidents are examined as to whether they are likely tooccur with SUVs:

I. The cause of the accident is related to the SUV driver's"eld of view.

f The pedestrian was struck by a one-box vehicle inreverse.

f The pedestrian using the crosswalk was struck bya SUV turning right.

f A read-end collision in which a SUV was involved.II. The cause of the accident is related to the vehicle

dynamics of the SUV.f A rollover accident involving a SUV.

4.1. Pedestrian accident from rear impact by vehicle(Case 1)

SUVs and one-box vehicles have a higher frequency ofrear-impact against pedestrians (Fig. 8). We examine thetype of accident where the one-box vehicle unknowinglybacked into a pedestrian. Fig. 10 shows the accident site.The accident occurred at 11:30 a.m., and the weather was"ne. When the driver (height 168 cm) was approachingthe parking lot, he "rst moved the vehicle forward to anopen space in front of the parking lot across the road(Fig. 11).

View was restricted by the curved road, and the driverwas watching out for other vehicles. However, he did notsee a pedestrian aged 87 who was walking on the side-walk with a handcart. The pedestrian was struck by therear of the vehicle and caught underneath it. The driverfound the pedestrian after he had stopped his vehicle inthe parking lot.

Compared with sedans, the rear view from the driver'sone-box seat is restricted, particularly lower down. It islikely that the curtains or head restraints on the seatobstructed the "eld of rear view. It was di$cult for thedriver to see the pedestrian because his height was lessthan 150 cm and he was pushing a handcart. The drivermight have seen the pedestrian had he checked theundermirror installed above the rear window of the ve-hicle. However, since the driver was in a hurry to park, hefailed to assess the situation su$ciently.

106 N. Takubo, K. Mizuno / JSAE Review 21 (2000) 103}108

Fig. 11. Rear view from the driver's seat (Case 1). Fig. 12. Accident site (Case 2).

Fig. 13. Accident site (Case 3).

4.2. Rear-end collision (Case 2)

The proportion of SUV accidents is high when theSUV strikes the rear end of the vehicle in front (seeFig. 4). Here a case was examined in which the SUVcrashed into the rear end of a car that had stopped whenthe SUV started to move.

Fig. 12 shows the accident site. The accident occurredat 8:40 a.m. and the weather was "ne. The SUV hadstopped behind several vehicles at an intersection. Afterthe tra$c signal changed to green, the driver of the SUVsaw the vehicles in front starting to move. The SUVdriver started his vehicle, and he noticed that the car justin front of his was not starting. He braked, but he couldnot avoid hitting the car in front which was equippedwith manual transmission, so that the driver was delayedby having to shift gears.

SUV drivers (like truck drivers) are seated so high thatthey have only a partial view of the vehicle immediatelyin front of them. Therefore, the driver of the SUV maylose attention to the forward car, which can be one causeof such accidents.

4.3. SUV roll-over accident (Case 3)

The proportion of the SUV rollovers is high in single-vehicle accidents (see Fig. 5). In this case, the rollover ofan SUV due to an abrupt change in steering is examined.

The SUV was in the outside lane of a three-lane ex-pressway travelling at 90 km/h. It was bu!eted bya strong wind from the right side (there was a caution ofside winds posted on the expressway). The driver wassurprised and attempted to correct his steering. The ve-hicle lost its balance, and "nally rolled over in the outsidetravelling lane. The accident site is shown in Fig. 13.

Considering the causes of the high rollover rate ofSUVs, these types of vehicles are likely to be driven oncurved mountain roads, and some SUV drivers have

reported characteristics of abrupt handling. The SUV'shigher center of gravity also makes it prone to rollovers,particularly when travelling at high-speed or in a sidewind, in contrast to sedans which are far more stable.

In this accident, two children (unbelted) were ejectedfrom the vehicle and one sustained a fatal injury. It isnecessary for all occupants, even those in the rear seats,to wear seat belts to prevent injuries following ejectionfrom the vehicle.

5. Discussion and summary

The vulnerabilities and situations underlying SUV ac-cidents are studied by statistics and in-depth analyses.The statistical analyses indicate that SUVs are especiallyprone to some types of accidents. The accident rate ofSUVs is higher than those of other vehicle types forpedestrian accidents, rear-end collisions, o!-road run-ning, rollover accidents, pedestrian impacts when turning

N. Takubo, K. Mizuno / JSAE Review 21 (2000) 103}108 107

right and backing up, child and elderly pedestrians acci-dents, young driver accidents, accidents during recre-ational use, and so on. Three accidents involving SUVwere analyzed.

Accident trends should be discussed from two points ofview: involvement in situations that may cause the acci-dent (exposure), and accident rates in such situations(accident risk). The former is related to the handling ofSUVs and driver factors, and the latter is related tovehicle structures and dynamics. The factors behind theaccident trend of SUVs are as follows:

(a) The characteristics of SUV usage are related to thecause of the accidents.

f The SUV is used for leisure and long-distance travel.f The SUV travels on crowded roads.f The SUV travels on unfamiliar roads to holiday

resorts where drivers may be distracted by the scen-ery.

f The SUV travels over winding roads in recreationalareas.

f The SUV often carries children.f The SUV travels at times and places of heavy pedes-

trian tra$c.(b) Driver factors of the SUV are related to the cause ofthe accidents.

f Young people are inclined to buy and drive SUVs.(c) Dynamics of the SUV are related to the cause of theaccidents.

Dynamics:f The driving feel and dynamics of SUVs are di!er-

ent from those of sedans.Vehicle shape and structure:

f The SUV center of gravity is so high that therolling motion is magni"ed.

f The side area of the SUV is so large that thevehicle is inclined to be adversely a!ected by sidewinds.

f The driver of the SUV has trouble spotting shortpedestrians like children and elderly people.

f Though the viewpoint of the driver is high, en-abling him to take in the tra$c situation in front,there is a risk that an overcon"dent driver maygrow careless.

As shown in the case studies, the main cause ofthe accidents is not the SUV itself. In most cases,accidents occur due to driver errors in perception, decisionand reaction. However, it is possible that the structuralcharacteristics of SUV foster such human errors. Furtherstudies analyzing SUV accidents are needed, since thenumber of SUVs, on the road will continue to rise.

References

[1] Institute for Tra$c Accident Research and Data Analysis: TheReport of Accident Investigation and Analysis in 1996 edition(1997).

108 N. Takubo, K. Mizuno / JSAE Review 21 (2000) 103}108