2006-01-1685

PARKING CRASHES AND PARKING ASSISTANCE SYSTEM DESIGN:

EVIDENCE FROM CRASH DATABASES, THE LITERATURE, AND INSURANCE AGENT INTERVIEWS

Paul GreenUniversity of Michigan Transportation Research Institute

Copyright © 2006 SAE International

ABSTRACT

This paper (1) summarizes previous human factors/safety research on parking (8 studies, mostly over 20 years old), (2) provides statistics for 10,400 parking-related crashes in Michigan from 2000-2002, and (3) summarizes interviews with 6 insurance agents concerning parking crashes.

These sources indicate:1. About 1/2 to 3/4 of parking crashes involve backing,

often into another moving vehicle while emerging from a parking stall.

2. Eight-and-a-half foot-wide stalls had higher crash rates than wider stalls.

3. Most parallel parking crashes occur on major streets, not minor streets.

4. Lighting and driver impairment were minor factors in parking crashes.

INTRODUCTION

This paper describes background information for the Nissan Around View Monitor (AVM) project, a video-based system to assist with parking, with the specific purpose of helping to design that system to the U.S. market. The product goals – to make parking safer, easier, and more comfortable for drivers – served to focus this review. Particular emphasis for all evaluations was given to collecting data on collision geometry, vehicle type, driver age, and other information that might indicate the situations for which a system might be useful, what the driver needs to see, and who might use it.

The electronics content of motor vehicles, particularly computer-controlled systems, has grown considerably over the last few years. These systems control the engine and drive train, control and deploy air bags, present information to drivers, and perform many other applications. These systems can enhance not only the

safety, but also the efficiency, usability, and convenience of motor vehicles.

Most research has focused on safety, with emphasis on the most severe and life-threatening crashes. In contrast, this research concerns parking-related crashes, which result in few deaths and injuries, but for which property damage is quite common. Parking is a difficult task drivers do not enjoy.

Accordingly, a significant number of devices have emerged in the market to make parking safer and easier. These include devices that use sonic sensors and provide audio feedback, usually in the form of a beep, when drivers approach an object. Other systems, such as those found on several current-model Infiniti vehicles, have rear-mounted cameras whose image is displayed on the instrument panel. These systems support backing maneuvers.

To aid Nissan in the development of a more sophisticated system, UMTRI conducted a number of experiments that involved collecting data on the size of parking spaces and how accurately people typically park (Cullinane, Smith, and Green, 2004), how well drivers parallel (Walls, Green, Gadgil, Amann, and Cullinane, 2004) and perpendicular park (Walls, Amann, Cullinane, Green, Gadgil, and Rubin, 2004) with camera systems that provide a 360 degree field of view, and the desired clearance around a parking vehicle (Gadgil and Green, 2005; Green, Gadgil, Walls, Amann, and Cullinane, 2004). All of those studies led to a set of design and evaluation guidelines that were summarized in a technical report (Rubin and Green, 2005). The current paper is an abridged version of the report written early in the project that examined the problem background (Smith, Green, and Jacob, 2004), namely the prior studies of parking, the relevant crash literature (in particular crashes in Michigan), and the experience of insurance agents with parking crashes. The author of this paper has taken the liberty of liberally reproducing

material from that report (Smith, Green, and Jacob, 2004) without providing exact page citations.

More specifically, questions of interest in those studies included:

1. What previous human factors research has been done on parking lot, driveway, and related crashes?

2. How often do various types of crashes (by collision geometry, vehicle type, driver age, etc.) occur at low speeds (25 mi/hr or less), especially those involving parking or driveways?

3. What do insurance agents say are typical characteristics of parking lot and low-speed crashes?

The answers to these questions should help determine which parking tasks could benefit from a parking assistance system. These answers will also (1) guide camera placement, aim, and field of view, (2) possibly provide suggestions for the desired image resolution and in-vehicle display location, and (3) possibly help identify the types of vehicles for which such systems are likely to provide the greatest safety and convenience benefits, as well as sales potential.

THE LITERATURE ON PARKING

A search of the UMTRI Library using “parking” and related terms uncovered less than a dozen items in that 40-year-old collection. Searching the web using Google.com and the same terms yielded no additional articles. The articles found primarily concerned crash rates as a function of the parking configuration (angled, parallel, or straight-in). Other issues included parking space turnover, driver characteristics, and parking space width. A summary of those articles (parking crashes, backing behavior), listed in chronological order, follows.

STUDIES OF PARKING CRASHES

Box (1981) examined private property crash reports for 1978 through 1980 from a single small city, Naperville, Illinois. Table 1 shows the number of crashes during that period in which a stationary vehicle was struck by a moving vehicle. Injuries were rare (1/525 crashes, driving in an aisle). Nearly 60 percent of parking-related crashes involved a stationary vehicle being damaged by a vehicle backing out of a parking space. (Vision is often limited in these situations, but could be supplemented by cameras). Crashes while pulling into a space constituted 21 percent of all crashes.

Table 1. Moving vehicle striking parked vehicle (Box, 1981)

Operation Category Property damage

only

Total %of

totalEntering a

spacePulling in 30 30 21

Backing out 9 9 3Leaving a

spacePulling out 13 13 5

Backing out 150 150 59Other Backing

(not to park)25 25 10

Driving in aisle

25 26 10

Driving between

parked cars

2 2 1

Subtotal 254 255 100Unknown 270 270

Total 524 525

Note: Based on other summary tables and the text, the original article appeared to contain erroneous counts for crashes involving an injury. Table 1 has been corrected accordingly.

Table 2 shows the distribution of crashes involving a moving vehicle striking another moving vehicle. Similar to Table 1, the movement most associated with crashes was backing out of a parking space. Again, injuries were rare (15/245 crashes).

Table 3 shows the types of fixed objects struck by a moving vehicle during a parking-related maneuver. Buildings were struck more than twice as often as any other category of objects (44 percent of crashes). Given that buildings are typically stationary and easy to see, the issue may be one of judging clearance, not of vision per se. Keep in mind that crashes involving a vehicle striking a fixed object only represent 6 percent of all parking-related crashes and, furthermore, perhaps many of the parking spaces were near buildings when the data were collected in Naperville 24 years ago.

Table 2. In aisles, moving vehicles striking moving vehicle (Box, 1981)

Operation Category Movement Property damage

only

Injury Total Percent of total

Leaving space

Pulling out 2 2 1Backing out 30 2 32 13

In parking access aisle

1 vehicle entering space

Pulling in 2 2 1Backing in 1 1 0

1 vehicle leaving space

Pulling out 4 4 1Backing out 104 104 43

Both vehicles driving forward

Sideswipe 20 2 22 9Head on

or rear end19 19 8

1 vehicle cutting across parking rows

4 3 7 3

At aisle intersection

44 6 50 21

Total 230 15 245 100

Table 3. Moving vehicle striking fixed object(Box, 1981)

Category Property damage

only

Injury Total % of total

Light pole 6 6 11Utility pole 2 2 4

Curb 1 1 2Building 22 1 23 44

Tree 3 1 4 8Fence 5 5 10

Other (signs, rocks, water)

9 1 10 19

Fall from fender

1 1 2

Total 47 5 52 100

Note: “Fall from fender” is not defined in the original report.

For a sample of parking lots where most of the crashes occurred, Table 4 shows crash frequency per space increased as parking turnover (3 undefined qualitative levels) increased. However, the differences in crash frequency as a function of stall angle are difficult to explain, 58 for 45 degrees, 80 for 60-75 degrees, and 19 for 90 degrees.

Table 4. Angle of stall relation to crashes/1000 spaces (Box, 1981)

Turnover classesStall angle (degrees)

Low Medium High Total

45-50 7.1 17.3 79.9 58.160-75 0.0 47.0 94.8 79.6

90 17.9 13.9 50.9 19.4Total 16.7 18.3 79.4 36.4

As shown in Table 5, parking space width had no overall effect, except that the crash frequency was greater for the narrowest stall width (8.5 feet), though the interactions with turnover were considerable. Since 1981 when this study was conducted, the vehicle fleet in the U.S. has changed considerably, with large, wide vehicles (SUVs, light trucks, minivans) comprising a much larger fraction of the vehicle fleet. Hence, these results should be applied with caution.

Table 5. Width of stall relation to accident rate(Box, 1981)

Stall width (feet)

Turnover classes TotalLow Medium High

8.5 11.8 95.2 28.0 53.19.0 17.8 17.6 71.6 35.19.5 16.0 3.5 118.5 30.610.0 25.6 18.1 69.2 39.5Total 17.6 17.4 77.1 35.4

McCoy, Ramanujam, Moussavi, and Ballard (1990) examined crash rates for 1985 and 1986 on 491 urban sections of Nebraska state highways that could contain on-street parking. Only crashes with parked vehicles and those resulting from parking maneuvers were included.

Overall, parking maneuvers led to 37 percent of all non–intersection crashes, crashes examined in detail in Table 6. Those crashes occurred more often on 2-way, 2-lane roads than on major streets, and less for parallel than angle parking.

Table 6. Percentage of parking crashes as a function of parking and road type (McCoy, Ramanujam, Moussavi,

and Ballard, 1990)

Type of parking Major streets

2-Way, 2-lane streets

Painted Parallel 33 46Low-angle - 77High-angle 44 81

Unpainted Parallel 21 39Angle 33 67

Readers should keep in mind that the various parking situations in Table 6 do not occur equally often. Table 7 shows non-intersection and parking crash rates respectively, that is, exposure-adjusted data. Interestingly, the conclusions are the same -- crash rates are greater for 2-way, 2-lane roads than major streets and that crash frequency (per space) is less for parallel parking than other types of parking. However, when adjusted for exposure, painting lines reduces crashes (in terms of frequency per stall).

Table 7. Non-intersection and parking crash rates (McCoy, Ramanujam, Moussavi, and Ballard, 1990)

Non-intersection ParkingItem Markings Type Major

streets2-Way, 2-

lane streetsMajor streets

2-Way, 2-lane streets

Crashes (million vehicle-miles)

Painted Parallel 1.65 1.83 0.550 0.848Low-angle - 3.38 - 2.60High-angle 1.20 3.59 0.533 2.91

Unpainted Parallel 1.32 0.674 0.284 0.264Angle 1.57 1.67 0.524 1.11

Crashes (10 billion vehicle-mile-hours/stall)

Painted Parallel 6.50 6.58 2.17 3.05Low-angle - 9.59 - 7.38High-angle 7.19 12.9 3.19 10.5

Unpainted Parallel 7.67 5.44 1.65 2.13Angle 13.19 12.10 4.40 8.04

An undated study by Seburn, probably from the mid to late 1960s, aggregated data from 32 cities in 17 states and the District of Columbia. Some 46 percent of crashes involved a vehicle traveling straight ahead on a roadway and colliding with a parking vehicle or one performing a parking-related maneuver (Table 7). As shown in Table 8, nearly 65 percent of parking crashes involved vehicles backing into or pulling towards a curb, and are likely associated with parallel parking.

Table 7. Number of crashes by vehicle operation

Vehicle motion Number %Traveling straight ahead 1639 46.0Entering a parking space 1211 34.0Leaving a parking space 355 10.0Turning (driveway or intersection)

352 10.0

Total 3557 100.0

Table 8. Number of crashes by parking operation

Parking maneuver Number %Backing into curb 414 26.4Pulling to curb-forward 609 38.9Pulling from curb-forward 378 24.1Stopped-not at curb 83 5.3Unknown 82 5.3Total 1566 100.0

Figure 1 shows the percentage of parking crashes by driver age groups, along with similar data for all crashes. The percentage of drivers in each category is not provided. There is a tendency for drivers under age 25 to be relatively more involved in parking crashes, which suggest they could benefit most from parking assistance devices.

02468

1012141618

20 & under

21-2526-3031-3536-4041-4546-5051-5556-6061-6566-70Over 70

Percent of Parking Crashes in Seburn (undated)Percent of All Crashes (National Safety Council)Percent of Drivers in That Age Group per NSC

Figure 1. Age of drivers involved in parking crashes (Saburn, undated)

Finally, Saburn (undated) concluded that lighting (or possibly fatigue) did not affect parking, even though 46 percent of all driving and 43.5 percent of all crashes occur at night.

Humphreys, Box, Sullivan, and Wheeler (1978) reported an analysis of street and crash data from 10 cities representing 5 states. Of the 4,800 crashes examined,

nearly 3,600 were midblock crashes or intersection crashes in which parking was deemed to be a factor. Parking was a factor in 54 percent of midblock and intersection crashes, and 85 percent of those crashes involved damage to the vehicles but no injuries (Table 9).

Table 9. Crashes by severity, street class, and parking involvement

Property damage only InjuryStreetclass

Parkinginvolved

Other Parkinginvolved

Other Total Percent parking involved

Local 396 133 37 37 603 72Collector 150 60 8 15 233 68Major 1229 1094 112 323 2758 49Total 1775 1287 157 375 3594 54

Table 10 shows 2-way major street midblock crashes by type and parking involvement. Parking was involved in all crashes where a vehicle hit a parked car, in 36.8 percent of crashes involving a pedestrian, and in about 5 percent of crashes where a vehicle struck another vehicle or a fixed object. Parking was involved in 43

percent of crashes on 2-way major streets, and a similar analysis for 1-way streets showed that parking was involved in 60 percent of crashes.

Table 10. Two-way major street midblock crashes by type and parking involvement

Type of parking involvement

On street

At driveway

Fixed object

Parked car Pedestrian Bicycle Misc Total

No involvement 518 315 154 0 24 9 16 1,036Open door 1 0 0 59 0 1 0 61Entering space 6 1 3 73 2 0 0 85Sight restricted 0 2 1 0 8 0 0 11Stationary 11 5 1 357 2 0 0 376Leaving space 8 6 4 222 2 0 0 242Parking subtotal 26 14 9 711 14 1 0 775Total 544 329 163 711 38 10 16 1,811Percent parking involved 4.7 4.2 5.5 100 36.8 10 0 43

Box (2001) reviewed published and unpublished curb parking studies from the 1970s through 2001 with the purpose of summarizing studies of parallel and angle parking, with an emphasis on angle parking. Several of those studies have been previously discussed. Of those not reviewed, several concerned small towns and a limited number of crashes. In general, they suggested that crash rates were lower for parallel parking than for angle parking.

STUDIES OF PARKING MANEUVERS

The predominance of backing-related crashes led to a focus on that maneuver. Harpster, Huey, and Lerner (1996) had 9 elderly and 12 young drivers back their own vehicles on public roads in real-world driving conditions. They are listed as a footnote to Table 11. That table shows that drivers glanced over their right shoulders while backing more than 50 percent of the time, which was 4 times greater than how often they looked over their left shoulders. Almost no glances were made to the dash during the backing tasks.

Table 11. Glance direction for each task (Harpster, Huey, and Lerner, 1996)

TaskGlance direction Total 1 2 3 4 5 6 7 8Forward 10.6 28.7 16.5 0.6 1.8 18.1 3.0 14.1 1.8Dash 0.0 0.1 0.0 0.0 0.0 0.0 0.0 0.1 0.0Driver’s mirror 8.2 6.0 3.6 8.4 7.8 14.7 11.6 2.8 11.0Rear mirror 4.5 4.7 7.4 4.0 1.7 4.5 2.3 6.3 5.1Right mirror 9.2 7.1 17.8 2.7 3.7 13.4 2.7 19.3 7.2Left window 2.3 1.5 0.3 0.2 0.2 4.9 1.3 0.0 0.0Right window 1.0 3.0 3.6 0.1 0.3 5.1 1.2 4.6 0.4Gear shift 1.0 3.2 -0.7 0.0 0.4 2.1 0.3 1.1 0.1Left shoulder 12.5 21.6 4.2 27.3 6.0 14.0 14.4 5.2 7.2Right shoulder 50.9 23.6 47.0 56.2 78.2 24.7 62.7 47.2 67.3

The 8 tasks included: (1) backing out of an angle slot in a parking lot, (2) parallel parking against a curb with vehicles in front, (3) extended curve backing to a stop point (location 1 of 2), (4) backing to a wall, (5) backing out of a perpendicular slot in a parking lot, (6) backing into a perpendicular parking slot, (7) parallel parking against a curb with vehicles in rear, and (8) extended curve backing to a stop point (location 2 of 2).

Given the restricted neck mobility of older drivers, there were major age differences in glance behavior (Table 12), with older drivers making greater use of mirrors and looking less over their right shoulder.

Table 12. Glance direction as a function of age across all tasks (Harpster, Huey, and Lerner, 1996)

Glance direction Young ElderlyForward 9.9 11.8Dash 0.0 0.0Driver’s mirror 4.3 15.0*Rear mirror 3.3 7.1*Right mirror 7.7 12.1Left window 0.7 1.5Right window 2.1 2.1Gear shift 0.4 1.8*Left shoulder 12.8 12.3Right shoulder 59.9 37.4*

Interestingly, as the drivers approached an object, they decelerated such that time to collision (TTC) remained relatively constant (Table 13). Although there were speed differences between younger and older drivers, there were no differences in minimum TTC.

Table 13. Minimum time to collision (MTTC) for all participants (s) (Harpster, Huey, and Lerner, 1996)

Task Mean Min 10th % Max2. Parallel 3.4 1.0 1.3 6.34. Back to wall 2.4 1.1 1.5 3.96. Back in

perpendicular 3.0 1.7 1.9 4.3

7. Parallel 3.7 2.0 2.1 6.3

The author was able to find only one study concerning parallel parking performance. Literature on this topic is extremely limited, even though it is a very common maneuver. As part of an experiment on steering effort levels that involved driving on city streets, an oval test track, and a slalom, Green, Gillespie, Reifeis, Wei-Haas, and Ottens (1984) had 43 Ford employees parallel park a 1984 Ford Thunderbird and a 1984 Ford LTD sedan. The number of vehicle movements was recorded but not reported, as the experiment concerned desired steering effort levels. One noteworthy tendency the author recalls was for a few subjects to continue moving in a particular direction until they hit something, especially when backing. Thus, in a parallel parking study, damage to the test vehicle or adjacent vehicles is expected.

SUMMARY OF THE HUMAN FACTORS LITERATURE

Thus, as a whole, these studies suggest that depending on the study, parking crashes represent between 1/3 and 1/2 of all police-reported crashes, and that backing out of an angle or perpendicular space is the most common scenario. For those parking maneuvers, drivers have more crashes with 8.5-feet wide stalls than with wider stalls. However, readers should keep in mind that many of the studies are from smaller cities. Further, the U.S. vehicle fleet has changed since many of these studies were conducted, with light trucks, SUVs, and minivans now being predominant. Some of these vehicles can be harder to see through, are much taller and wider, and have a much higher driver eye position.

Furthermore, there is a dearth of studies from urban areas.

Only one study could be located with data describing driver-backing behavior. It showed that older drivers had different scanning patterns than younger drivers (fewer direct looks to the right side but more use of mirrors) and that backing occurred with a constant TTC of about 3 seconds.

PARKING CRASHES IN MICHIGAN

All police-reported crashes in the state of Michigan from 2000, 2001, and 2002 were examined. In Michigan, a traffic crash is defined as an incident involving a motor vehicle, in transport, on a roadway, that resulted in death, injury, or property damage of $400 or greater. Michigan data were selected because they are reasonably typical of the U.S.; contain a mixture of urban, suburban, and rural settings; and were reasonably accessible.

Of the 1.2 million crashes in the database, about 10,000 or 1 percent were coded as entering or leaving parking. However, the actual number of parking-related crashes is much larger as police-reported crashes mostly concern public roads but many parking-related crashes occur on private property, and therefore are often not in the database. As noted in Table 14, the number of crashes declined over the 3 years examined, with crashes involving leaving a space being 2.6 times more likely than crashes entering a space.

Table 14. Summary of crashes associated with entering and leaving parking

Crash type

Item Year Total2000 2001 2002

Park Enter 1058 978 858 2894Leave 2818 2542 2207 7567Total 3876 3520 3065 10461

All # Fatal

1237 1206 1175 3618

# Injury

87043 80922 80567 248532

Total 424852 400813 395515 1221180

As shown in Table 15, men were about 15 percent more likely to be involved in parking-related crashes.

However, their exposure (were there more male drivers, did they drive and park more often?) was unspecified.

Table 15. Number of crashes by year, age, and sexW=women, M=Men, U=Unknown

Age

Year

Total2000 2001 2002

W M U W M U W M U≤30 626 640 15 528 561 26 437 493 15 3341

31-65 739 806 17 667 751 35 614 667 30 4326≥66 169 211 3 164 202 9 144 162 6 1070

Unknown 97 182 371 100 151 326 61 162 274 1724Total 1631 1839 406 1459 1665 396 1256 1484 325 10461

Impairment did not contribute substantially to parking crashes. Over the 3-year sample, factors that were examined as causing or contributing to crashes included alcohol (2.0 percent), drugs (0.15 percent), distractions (0.25 percent), and cell phone use (0.15 percent). The phone data probably underestimate the current situation as phone use while driving has risen markedly since 2002.

As shown in Table 16, most parking crashes occur in daylight hours, though exposure data to determine the relative risk of such crashes were not provided.

Table 16. Number of crashes by time of day and year

YearTime of day

9P-3A 3A-9A 9A-3P 3P-9P Unk2000 374 312 1587 1537 662001 279 274 1354 1403 2102002 246 221 1224 1231 143Total 899 807 4165 4171 419

Figure 2 shows parking-related crashes were evenly distributed among the months of the year, with the fewest crashes (7.2 percent) in February and the most crashes (10.1 percent) in December. The December peak could be due to increased parking associated with holiday-season shopping.

0.0

2.0

4.0

6.0

8.0

10.0

12.0

Jan Feb Mar AprMay Jun Jul AugSep OctNovDec

Figure 2. Percentage of total parking-related crashes (years 2000-2002)

In 79.1 percent of parking-related crashes, the first harmful event to occur was also the most harmful event of the crash. Table 17 shows the events associated with the highest crash incidences. Colliding with a motor vehicle in transport (vehicle in motion) accounted for 70 percent of all parking-related crashes between 2000 and 2002, followed by colliding with a parked vehicle (13 percent), and loss of vehicle control (3 percent).

Table 17. First harmful event of parking-related crashes

Entering parking Leaving parkingNon-fixed

objectMotor vehicle in transport 1476 51.0% 5896 77.9%

Parked vehicle 872 30.1% 510 6.7%Pedalcycle 22 0.8% 122 1.6%Pedestrian 15 0.5% 44 0.6%

Fixed object Curb 24 0.8% 9 0.1%Building 24 0.8% 4 0.1%Fence 14 0.5% 3 0.0%

Utility pole 8 0.3% 14 0.2%Non-collision Loss of control 106 3.7% 156 2.1%

Cross centerline/median 11 0.4% 100 1.3%Ran off road right 25 0.9% 26 0.3%

Re-enter road 8 0.3% 59 0.8%

Table 18 shows the consequences of parking-related crashes. Nearly 85 percent of parking-related crashes involved only property damage to the vehicle. The remaining crashes primarily involved injuries to the driver and vehicle passengers, with less than 1 percent of all parking-related crashes involving a pedestrian.

Table 18. Parking-related crash implications

Crash Type 2000 2001 2002# % # % # %

Property damage

only

3292 85 2998 85 2589 85

Injury crash (no deaths)

582 15 520 15 474 16

Pedestrian 29 1 33 1 24 1

Table 19 shows that passenger cars or station wagons accounted for nearly 70 percent of parking-related crashes, followed by pickup trucks with nearly 12 percent, motor homes or vans with about 9 percent, and motorcycles with less than 1 percent. The percentages are fairly stable over the 3-year period. Since the prevalence of each vehicle type was not considered, the data do not necessarily indicate that passenger cars were involved in more accidents than any other type of vehicle.

Table 19. Prevalence of vehicle types involved in parking-related crashes

Crash type

2000 2001 2002# % # % # %

Car or station wagon

2686 69 2379 68 2091 68

Pickup 433 11 439 13 370 12Motor-home or van

369 10 311 9 262 9

Motor-cycle

6 0 10 0 10 0

Figure 3 shows where vehicles were struck or struck other vehicles when parking. When entering parking, most damage occurred to the front or passenger side of the vehicle. When leaving parking, nearly one-third of all vehicles had the greatest amount of damage to their left front corner. This could occur when a vehicle is pulling forward out of a parallel parking space and is struck by another vehicle traveling in the roadway. Keep in mind that these data are from primarily road-related crashes, not parking lot crashes, so the number of backing crashes (and rear-end damage) in the database is limited. Also, because these crashes can involve high speeds, there are some rollovers and other crashes for which roof damage will occur.

Figure 3. Location of greatest vehicle damage from parking-related crashes

Table 20 shows the varying extent of damage associated with entering and leaving parking. Leaving parking was associated with fewer instances of slight to no damage than entering parking. However, leaving parked was also associated with more instances of moderate and greater damage, as exiting crashes tended to be more severe.

Table 20. Extent of vehicle damage from crashes while entering and leaving parking

Extent of Damage

Entering parking Leaving parking

No damage (0) 439 15.2 % 639 8.4%

Slight damage (1 or 2)

1832 63.3% 4622 61.1%

Moderate (3 or 4)

388 13.4% 1628 21.5%

Heavy 30 1.0% 100 1.3%Not Repairable 9 0.3% 43 0.6%

Thus, the crash data suggest that parking crashes more commonly involve leaving a space than entering one (by a factor of 2.6), occur slightly more often for men, occur primarily during the daylight hours, rarely involve loss of control, and generally (70 percent) involve no or only slight damage. When there is damage, it is generally property damage (85 percent), with no area on the car more likely to be damaged than another. However, keep in mind that many parking-related crashes are unreported, and these data concern absolute numbers, not risk, where measures of exposure are needed. In terms of engineering solutions, these data suggest the need to focus on supporting leaving from parking spaces, but not to be concerned about lighting (since most crashes occur in the daytime).

INTERVIEWS OF STATE FARM INSURANCE AGENTS

DATA COLLECTION METHOD

Because many parking crashes occur on private property and are not recorded in public databases, information was sought from those familiar with such crashes, namely insurance agents. In the most states in the U.S., all licensed vehicles must be insured, and even minor crashes often lead to claims.

For this project 6 State Farm insurance agents were interviewed about their experience processing claims of crashes related to parking. State Farm is one of the largest automotive insurers in the U.S. and has a strong presence in Michigan. Five of the agents were interviewed in person at their respective offices in the vicinity of Ann Arbor, MI, and a sixth agent from Holland, MI was interviewed by telephone. The Ann Arbor interviews were audiotaped or videotaped. The first agent (actually, the office manager) interviewed served as a pilot subject, and her responses were not included in the final analysis. All subjects were volunteers and not paid for their time. Interviews could last up to an hour each.

After having agents complete a consent form, the interviewers inquired about the client and vehicle demographics insured by the agent, and then prompted the agent to provide a narrative of the most recent 2 or 3 parking or low-speed maneuver-related crash claims they could recall. Following the narrative, each agent was asked a predefined set of questions. They included questions about the types of customers they insure (students vs. local residents, ages, professions, U.S. vs. foreign born, etc.) and descriptions of 2 or 3 recent claims that involved parking.

Those claims were explored in great detail. Those details concerned a general description of the scenario (where and when the crash occurred, the amount of injury or property damage, the road surface condition, the weather, the visibility and lighting, and the maneuver involved (e.g., turning right into a stall at a particular parking lot). Also obtained were details on the other object. (Did the driver see it? Was it moving? If there was another driver or a pedestrian, was there eye contact? How old the other person was if another person was involved? Was the other person incapacitated by drugs, alcohol, or limited for some other reason? Were there other occupants? What type of vehicle was driven? How could the crash have been presented?) Although the questions were listed in a particular order, the interviews were free flowing and often not answered in the order given. It is important to emphasize that even though a great deal of information was obtained, and the interviewers were careful that the information provided did not uniquely identify an individual.

The insured customers about who were described by the agents were not a representative sample of U.S. drivers. Ann Arbor, Michigan, is a college town attended by a large number of foreign students. Although the insured sample has a wide variety of ages, ethnicities, and professions, 3 of the 5 agents indicated that they processed more claims from younger drivers than from other age groups. Additionally, 2 agents stated having more claims from international clients than others.

Customers for 3 of the agents primarily drove sedans and sport-utility vehicles, while the other 2 agents insured a reasonable amount of pickup trucks. The majority of agents insured equal numbers of small and large vehicles. All agents indicated that their clients possessed relatively late-model vehicles, with an estimated mean age of less than 5 years.

WHAT WERE TYPICAL CRASHES?

Four of the 5 agents described 2 or 3 specific parking crashes, while the remaining agent offered a more general account of those types of crashes. Those 4 agents described a total of 10 crashes involving 20 vehicles, although not every single detail of each crash could be recalled. Some of those crashes were only observed by the agent, and not the subject of an insurance claim they processed. No reported crashes involved pedestrians or injuries. The amount of property damage was highly dependent on the type of vehicles involved and their speed at impact.

Although many potential causes were cited, most common were poor parking lot design, human error from inattentiveness, and lack of driver experience. The majority of crashes reported by the agents occurred in parking lots, and 4 of the 10 crashes were directly related to a parking maneuver. Of the 10 crashes, none was associated with entering a parking space, 4 were associated with leaving a parking space, and 6 were associated with low speed maneuvers.

Three of 4 of the parking-related crashes involved straight-in parking, while the other crash was a vehicle backing out of angled parking. That trend more likely indicates the greater availability of straight-in parking spaces rather than a greater crash risk. It is interesting that one agent stated, “Angled parking spaces are easier to get in and out of than straight-in parking spaces.”

Of the vehicles involved in parking crashes reported by agents, 3 involved contact with a stationary vehicle and 1 with a moving vehicle. The 3 stationary vehicles that were struck were located adjacent to the vehicle leaving a parking space, across the parking lot aisle, and stopped in the parking lot aisle. The remaining crash involved a vehicle moving down the parking lot aisle. All the vehicles involved in low-speed crashes reported by agents were moving forward (Table 21). As noted before, almost all parking-related crashes were caused by a backwards-moving vehicle, and all low-speed

crashes involved forward-moving vehicles. Three of the 5 agents personally felt that “backing out” of parking spaces and driveways were the most common scenarios in which a crash would occur. One agent commented: “More people are on ‘auto pilot’ when backing out of driveways.”

Table 21. Movement of vehicles involved in crashes

Forward Backwards StoppedParking related

1 4 3

Low-speed

12 0 0

In terms of the driving context, 6 of the 10 crashes occurred on dry pavement, while ice, snow, and gravel was each represented once (Table 22). All combined, the agents recalled the weather conditions of 8 crashes. The majority (7) occurred in clear weather and just 1 low-speed crash occurred in, and was said to be caused by, snow. The light levels were noted as bright in 6 of 8 crashes, as dim in 1 crash, and as night in another.

Table 22. Road surface condition during crash occurrence

Dry Gravel Snow Ice

No info

Parking related

4 0 0 0 0

Low- speed

2 1 1 1 1

The agents reported that the majority of crashes involved 2 vehicles, rather than a vehicle and a fixed object.

WHO WERE THE DRIVERS?

Of the 19 drivers, 16 were recalled, 8 men and 8 women. Of them, the ages were recalled for 13 drivers: 8 were 16 to 28, 4 were 38 to 50, and 1 was 70. In the 10 crashes, no driver was incapacitated by medication, drugs, alcohol, or physical disability.

In 4 of the 10 instances, agents felt people drove too fast given their experience and the road conditions. Agents recalled the sight conditions for only 8 of the crashes, and in 5 of them the driver could see the other vehicle. There was only 1 reported case of eye contact between drivers.

HOW COULD PARKING CRASHES BE PREVENTED?

Most agents believed the main problems were the design of parking facilities and human errors deriving from inexperience, inattentiveness, and non-compliance with the basic principles taught in driver’s training. When

prompted, the agents offered the following ideas to help drivers avoid parking-related crashes:

A device to help the driver see behind their vehicle without having to back out too far

Large round mirrors installed in parking lots and driveways to provide drivers a better view of their surroundings

A device that beeps to indicate the presence of vehicles within a 100-foot radius around the vehicle (it would activate only while the car is moving and not in heavy traffic on a roadway)

A camera that provides a panoramic view of the rear of the vehicle

Sensors to detect and alert drivers to vehicles in the driver’s blind spots

CONCLUSIONS

The conclusions that follow are based on all 3 sets of data, none of which is perfect, and most of which focus on parking crashes, the primary crash type of interest. Many of the studies are 20 or more years old, representing times when cars predominated the vehicle fleet and traffic density was much lower. The current U.S. mix of cars, minivans, SUVs, and light trucks can make seeing other vehicles (and the boundaries of one’s own vehicle) quite difficult in parking maneuvers. Accordingly, the problems and consequent frequency of crash types may have also changed.

Secondly, the Michigan crash data, a representative sample of police-reported crashes for a state with geography and a vehicle fleet typical of the U.S., primarily concerns crashes on public roads, not private property such as parking lots and garages. Hence, some of the desired crash data is missing from that set.

Finally, while the information from insurance agents was useful, the sample size was small.

However, in spite of these limitations, the findings from each of these sources are mutually reinforcing.

1. Depending on the source and data set, anywhere from 1/2 to 3/4 of all parking crashes involve backing from a parking spot, primarily from a parking stall. Most commonly, the crash involves striking another vehicle moving in the aisle, not a parked car.

2. Crashes at parking lot aisle intersections generally occur because drivers are moving too quickly, but sometimes because there are no stop signs to regulate traffic flow.

3. When crashes involve fixed objects, a building is the most commonly struck object.

4. The literature suggests that crash rates are higher for 8-1/2-foot stalls than for wider stalls, but the data are

from a time when vehicles were much smaller and more likely to be cars.

5. Most parallel parking crashes occur on major streets.

6. Men account for a slightly greater fraction of parking crashes than women, but it is uncertain if there is a difference when considering exposure (e.g., miles driven, number of parking events).

7. No age group is more likely to have parking crashes when the frequency of parking crashes is compared with their overall crash rate. Keep in mind that very young drivers are relatively more likely to be involved in all types of crashes including parking-related crashes.

8. Impairment due to alcohol and drugs is a relatively minor factor in parking crashes.

9. Lighting does not seem to be a factor in parking crashes. Day/night differences seem to reflect exposure to those conditions.

10. There are few month-to-month differences in parking crashes, except that more crashes occur in December than any other month, possibly due to shopping-related parking during the holiday season.

11. When backing up, the most common place to look is over the right shoulder.

The literature, the crash data from Michigan, and insights from the insurance agents all point to the potential value of a system that would allow drivers to see down a parking aisle when backing out of a stall into an aisle or street. The system should provide visual or other types of information to the rear and sides of the vehicle for backing from both perpendicular and angled stalls. Often the driver cannot see around other vehicles, in particular vans, minivans, light trucks, and SUVs, which, as a group, comprise over 50 percent of the new vehicles sold in the U.S.

A secondary opportunity is assisting with parallel parking on major (presumably busy) streets, though there is less evidence pertaining to that situation.

In addition, the data suggest that studies should certainly include young drivers (who are most likely to be involved in crashes) and evaluate 8-1/2-foot-wide stalls for perpendicular and angle parking (since there are more crashes for that width), but do not need to consider impairment due to drugs or alcohol.

Though these findings should hold for most of North America, it is uncertain how differences in traffic density, the types of parking available, the speeds on public roads, the sizes of vehicles available, geography, and even driver aggressiveness, are likely to influence the

application of these results to South and Central America, Europe, or Asia.

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Walls, S.M., Amann, J., Cullinane, B., Green, P., Gadgil, S., and Rubin, R. (2004). Alternative Images for Perpendicular Parking: A Usability Test of a Multi-Camera Assistance System (Technical Report UMTRI 2004-17), Ann Arbor, MI: University of Michigan Transportation Research Institute.

Walls, S.M., Green, P., Gadgil, S., Amann, J., and Cullinane, B. (2004). Alternative Images for Parallel Parking: A Usability Test of a Multi-Camera Assistance System (Technical Report UMTRI 2004-31), Ann Arbor, MI: University of Michigan Transportation Research Institute.

ACKNOWLEDGMENTS

This research was supported by Nissan Motor Company whose support is gratefully acknowledged. Dan Smith (now with Toyota) and Renju Jacob provided significant contributions to the original technical report on which this paper is based.

CONTACT

Paul GreenUniversity of Michigan Transportation Research Institute (UMTRI)Human Factors Division2901 Baxter RoadAnn Arbor, Michigan 48109-2150 USApagreen@umich.eduwww.umich.edu/~driving