Thesis Defense Presentation: A Human Factors study of Child Restraint System Use and Misuse

Thesis Defense:

A Human Factors Study of Child Restraint System (CRS)Use and MisuseJuly 24, 2009

Peng YangCandidate for Master of Science in DesignConcentration in Human Factors in Design

Committee: Donald Herring (Chair) John Takamura Russell Branaghan

1

Introduction

• In the United States, motor vehicle crashes are the leading cause of death for children

younger than 14 years old*.

• Occupant restraint systems, or called “Seat Belts”, were invented to provide protection

for adult passengers.

• Seat belts are not suitable for children under 14

2* Source: National Highway Traffic Safety Administration. (2007). Traffic safety facts: 2007 Data [DOT HS 810 987]. Washington, DC. NHTSA.

2

Child Restraint System (CRS) has been introduced to protect child passengers in vehicles.

Studies had demonstrated CRS’s effectiveness in reducing the risk of child fatalities and serious injuries in the event of a car crash.

3

4

1 2

3 4

4

MISUSE

“any deviation from intended application and use which might reduce the protective performance of the child restraint system” - ISO-13215

International Organization for Standardization. (1999). ISO-13215 Road Vehicles- Reduction of misuse risk of child restraint systems- Part 3: Prediction and assessment of misuse by

Misuse Mode and Effect Analysis. pp. 12

5

6

It becomes a product designer’s responsibility and interest to explore the learning process of CRS users and discover their successes and difficulties in using CRS correctly.

This study is intended to examine multiple aspects of usability issues and design problems of existing CRS's and to find potential design solutions.

6

Design Insights

Framework

7

Literature Review

Studies of CRS Misuse

Study 1: Interviews

Study 2: Installation Experiment

7

8

Decina & Knoebel(1997)

Decina & Lococo(2005)

Decina & Lococo(2007)

Raw Data Provided by Safe Kids Local

Coalition

Observed

Misuse Rate

Common Misuse

5,900 children under 60 pounds in four states in 1995

5,572 children under 80 pounds in six states in 2002

1,000 children in LATCH- compatible vehicles in 2005

912 CRS’s brought to check events at Maricopa County, AZ (Jan 2006 - Oct 2008)

Infant Seats: 79.4%Convertible Seats: 81.1%

Overall: 72.6% critically misused

20% of the CRS’s were installed by using LATCH and seat belt

Overall: 90.5%

Loose harness strapsLoose attachment

Loose harness strapsLoose attachment

Loose LATCH beltsLoose harness

Loose attachmentLoose harness

Decina, L. E., & Knoebel, K. Y. (1997). Child safety seat misuse patterns in four state. Accident Analysis and Prevention, 29 (1), 125-132.

Decina, L. E., & Lococo, K. H. (2005). Child restraint system use and misuse in six states. Accident Analysis and Prevention, 37, 583-590.

Decina, L. E., & Lococo, K. H. (2007). Observed LATCH use and misuse characteristics of child restraint systems in seven states. Journal of Safety Research, 38 (3), 273-281.

Safe Kids Coalition of Maricopa County. (2009). Misuse Checklist Stats of Maricopa County. Unpublished raw data.

8

9

1. Can this CRS be used right out of the box?

2. Can the “average” user install a CRS securely with little efforts?

3. Is there adequate guidance and immediate feedback from the product?

4. What are the possible design solutions?

research questions

9

Study 1: interviews

• Seven current CRS users were interviewed to collect data about user activities and

experiences involving CRS use.

• Semi-structured protocol and “Think Aloud” approach

• Experiences and activities

• How easy or difficult some components to use

• Confidence level

• The use of the owner's manual and labels

10

10

11Subject #1-2 is seen restraining her baby within a convertible seat

11

12

Adoption

Daily UsePre-Installation Configurations

Installation (CRS-in-Vehicle)

Restraining (Child-in-CRS)

Removal

Maintenance

Moving to the Next Step

Activity Model

12

13

After interviewing the seven participants, the present study was able to identify almost every type of misuse reported in previous studies.

Incorrect recline angleUse of the after-market accessoriesIncorrect lower anchorsLoose harness strapsIncorrectly positioned retainer clipUsing both LATCH and seat beltMisrouted beltsMisrouted harness strapsMisconception on harness tension...

Study 1: results

13

14

after-market products

14

15

Subject #1-3Incorrect LATCH components were used

15

16

Subject #1-4 Misrouted belts and used LATCH system and seat belt together

16

No29%

Yes71%

No57%

Yes43%

Did you send out the registration card? Do you keep the manual with the seat?

17

n=7

17

Less than 5 min83%

No Time Limit17%

15-20 min17%

10-15 min17%

6-10 min33%

No Time Limit33%

In your opinion, what is the reasonable amount of time to learn how to use car seat in the first time?

In your opinion, what is the reasonable amount of time to install a car seat in daily use?

18

n=7

18

Study 2: installation experiment

19

• A total of 16 inexperienced CRS users participated the experiment.

• 11 of the participants were ASU students or staff, 5 participants were recruited from

staff workers at a local daycare center and expecting parents who registered for a pre-

birth class at a local hospital.

• Participants were randomly divided into 2 group:

• Manual Group (10 Participants: 7 Female, 3 Male)

• No-Manual Group (6 Participants: 3 Female, 3 Male )

19

20

2008 Chevy Impala LSLATCH-compatible full size sedan

20

21

Cosco® Scenera® Convertible Car Seatwas chosen due to the mixed considerations of brand, price, local popularity, and representativeness of CRS design features.

Rear-FacingFrom birth to 1 Year Old5-35 lbs19-36 in.Forward-FacingOver 1 Year Old 22-40 lbs34-43 in.

harness slots

retainer clip

harness buckle

harness straps

harness release button

rear-facing belt path

forward-facing

belt path

21

22

http://www.youtube.com/watch?v=1dJbYUmWpSY

22





23

Experiment Procedure

1. Read the pre-test educational materials

2. Read the test CRS’s owner’s manual (Manual Group only)

3. Participants were prompted to “play with” the CRS

4. Install the CRS based on their own understanding, and the

manual (Manual Group only) and then restrain an infant-sized

doll (2-month old, 21” and 10.5 pounds)

5. A certified technician checked the participants’ installations

23

Success rate

• None of the participants completed the tasks 100% correctly according to the best

practice.

• Only one participant (subject #2-5, in the No-Manual Group) ended up an installation

that was acceptable *

• Overall success rate is about 6.25%.

24* Rudin-Brown et al. Behavioral Evaluation of Child Restraint System (CRS) Label/Warning Effectiveness. Traffic Injury Prevention (2004)

24

Time-on-task

25

0

200

400

600

800

Manual Reading Pre-Installation Installation Restraining

70

665

186.792.5

730

287

542

time

(in s

econ

ds)

Manual GroupNo-Manual Group

25

Error frequency

26

Manual Group (n=10)

No-Manual Group (n=6)

very loose attachment (seat moves more 4”)

incorrect recline angle

harness slots are higher than the child’s shoulders level

harness straps are too loose

retainer clip is positioned too low

wrong belt path

harness buckle unfastened

wrong direction

CRS is placed in the front seat

100% 83.3%

90% 100%

80% 100%

70% 100%

30% 100%

40% 33%

20% 16.7%

10% 33%

0 16.7%

26

Installation: position & direction

27

Subject #2-16 (No-Manual Group)The seat is being installed in the front seat while airbags are active

Subject #2-6 (Manual Group) The seat is installed facing the front of the vehicle

Incorrect Direction18.75%

27

Installation: belt path

28

Subject #2-3 (Manual Group)The seat belt is routed through a wrong belt path and very loose

Incorrect Belt Path37.5%

Subject #2-9 (No-Manual Group)The seat is misrouted through a non-relevant structure

28

Installation: recline angle

29

Subject #2-8 (Manual Group)Pulls down the recline stand to comply with the recline angle sticker

Subject #2-12 (Manual Group)The seat belt is positioned too upright

Incorrect Recline Angle: 93.75%

29

Restraining: harness system

30

Subject #2-15 (Manual Group)The harness straps are very loose

Subject #2-12 (Manual Group) moves the harness straps to a higher slots, which is a critical misuse

Incorrect Harness Slot Selection: 93.75%

Loose Harness81.5%Retainer Clip Too Low56.25%

30

Restraining: harness buckle

31

Subject #2-11 (No-Manual Group)The harness straps were not correctly attached.

Subject #2-13 (Manual Group) failed to fasten the harness buckle between the child’s legs

Harness Buckle Unfastened: 18.75%

31

LATCH?

32

no one completed the installation exercise by using the LATCH.5 participants tried to use the LATCH but all failed, including one quit.

32

Inappropriate Use of LATCH

33

Subject #2-5 (Manual Group)is trying to attach top tether strap with the bottom structure of the front seat

33

34

Subject #2-10 (Manual Group)The top tether strap is seen connected to the LATCH anchor, which is not necessary for this test CRS’s rear-facing installation

Subject #2-2 (No-Manual Group) connects the top tether strap to the front seat

34

Everybody recognizes it? or do they?

35

The pictogram shows the correct position of the retainer clip, however, most participants did not pay attention to it.

35

36

Only 3 of the 16 participants appeared to have noticed this sticker and eventually only one of them ended up a correct recline angle

Everybody recognizes it? or do they?

36

Connections?

37

Pictogram found in the manual

An actual lower anchor found in the

vehicle

37

Ease-of-use (EOU) ratings

Adoption

Position

Directio

n

Attachment

Belt & Buckle Selectio

n

Belt Path

Belt Tension

Restraining

Harness Slots

Retainer Clip

Harness Tension

Release Child

Remove Seat

1 2 3 4 5


Very Difficult Very Easy

38

Adoption

Position

Directio

n

Attachment

Belt & Buckle Selectio

n

Belt Path

Belt Tension

Restraining

Harness Slots

Retainer Clip

Harness Tension

1 2 3 4


Not Confident Very Confident

Confidence level

39

Summary of findings

• Learning Experience

• High Learning and Cognitive Load

• The information is too complex

• Misleading CRS components and design features

40

40

Summary of findings

• Lacking of adequate guidance and operation feedback.

• No difference between car seats in different price ranges

• Benefit of observing first-time Users

41

41

limitations

• Methodological issues

• Study Limitations

• Representativeness of the sample

• The test convertible seat and test vehicle

• Performance tasks

42

42

What can designers do to make car seats easier to learn and use?

43

Make Things Simple

• Design adjustments should

• Not act in a manner contrary to user expectations. Counter-intuitive use should be

avoided

• Be kept as simple as possible to perform (Rudin-Brown et al. 2003)

• Utilize the operation and features that users are familiar with

• Provide automatic or self-adjusting components

44

Rudin-Brown, C. M., Kumagai, J. K., Angel, H. A., Iwasa-Madge, K. M., & Noy, Y. I. (2003). Usability issues concerning child restraint system harness design. Accident Analysis

Prevention, 35, 341-348

44

Make Things Visible

• Not everybody knows

• “Design Them Out” (Laughery, 1993)

• Make components more visible, easy to locate and identify

• Relationship between each component should be easily understood

• LATCH components should be painted unique color

• “Equally obvious”

45

Laughery, K. (1993). Everybody knows - or do they? Ergonomics in Design, 1, 8-13.

45

Another example of the existing rear-facing belt paths. Users need to read the labels carefully because the path is hidden too much

46

Provide Performance Feedback

• Static feedback

• arrows on the labels, color-

coding, graphic design, etc.

• misuse self check

• Dynamic feedback

• tension meter

• attachment alarm

• recline angle indicator

47

A recline angle indicator equipped on a convertible seat. The information is still too complex and hard to read.

47

Instructions and labeling

• Information should be well organized and clearly presented.

• How users understand and interpret pictograms should be carefully examined.

• Video Instructions

48

48

Context of product use

49

Designers should consider the “real-world” of product use

49

LATCH system

• The ease of LATCH use should be highlighted in all materials

• Give a big and clear photograph of how a correctly installed CRS looks like

• Storage area for LATCH belts and seat belt components

50

50

implication for future research

• Qualitative Data vs. Quantitative Data

• Incorporate a larger sample size

• Next step study:

• what are the design features that users are familiar with? what prior knowledge and

experience do parents and caregivers have?

• factors contributing to experienced users’ misuse

• potential misuse models within the whole life cycle of CRS use

51

51

52

Bottom-line for CRS designer:1. Recognize both the cognitive and physical characteristics of CRS

users.

2. Conduct ongoing usability studies and user research, and incorporate users in the product development process.

3. Avoid those confusing and misleading design features and incomprehensible descriptions in any written instructions.

52

53

I would like to thank all participants and technicians that were involved. A special thank you to people I met at the Child Passenger Safety technician course at the Gila River Indian community.

53

54

Thank you!

54