Montréal Crossing - The Hazards of Intersections

Xing Jian Liu (M3 – McGill University)Dr. David Kaiser (R5 – PHPM)

Faculty Supervisor: Dr. Joseph Cox (MScPH Program, McGill University)

Debrief

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Tell us about your findings!

• Did you observe any events?

• What risk factors did you identify?

• Any interesting interventions that you observed or dreamed up?

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Key concepts: types of variables• Variable: any characteristic, number, or attribute that

can be measured or counted

• Numeric variables have values that describe a measurable quantity as a number, like 'how many' or 'how much'

• May take any real number value (continuous) or only whole number values (discrete)

• The data collected for a numeric variable are quantitative data

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Key concepts: types of variables• Variable: any characteristic, number, or attribute that

can be measured or counted

• Categorical variables have values that describe a 'quality' or 'characteristic' of a data unit, like 'what type' or 'which category'

• Categories should be mutually exclusive (in one category or in another) and exhaustive (include all possible options)

• May have a natural order (ordinal) or not (nominal)• The data collected for a categorical variable are qualitative data

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Exercise: types of variables• What kinds of data did you

collect? Take 5 minutes to categorize

your findings according to the type of variable that you might use to describe them.

Source: Australian Bureau of Statistics, 2013

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Key concepts: measures of occurrence• Incidence• Measure of the speed at which new events arise in a

population during a fixed time. Can be expressed either as a proportion or as a rate.

• Incidence proportion (risk) =

• Incidence rate (person-time rate) =

Source: The Association of Faculties of Medicine of Canada (2013), CDC (2013) http://phprimer.afmc.ca/inner/primer_contents

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Key concepts: measures of occurrence• Prevalence• Measure of disease state• Counts all existing cases in a fixed time period (including

those that began before the observation period), divided by the population size.• Influenced by both the incidence and by the duration of the

illness.

• Point prevalence: prevalence of a disease state at a specific point in time

Source: The Association of Faculties of Medicine of Canada (2013), CDC (2013)http://phprimer.afmc.ca/inner/primer_contents

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Exercise: measures of occurrence• What could you measure with the data you collected?

Take 5 minutes to think about whether your observations could be used to determine incidence proportion, incidence rate, or prevalence of injuries, collisions or near misses assume that you have data on the number of events if you did not

observe any

Are you missing any information?

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Key concepts: the epidemiological triad

Source: The Association of Faculties of Medicine of Canada (2013)http://phprimer.afmc.ca/inner/primer_contents

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Key concepts: the epidemiological triad

Host = Pedestrians

Agent = Kinetic Energy

Environment = Physical & Sociocultural

Vector = Vehicles

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Key concepts: accident vs. injury• An accident:• Is an unforeseen event• Assumes unpredictability and inability to prevent

• An injury event:• Is predictable based on knowledge of its determinants• Can predict number, distribution, and trends on a population

level (not necessarily individually)• Appropriately designed preventive interventions can reduce

the number of injuries

Source: The Association of Faculties of Medicine of Canada (2013)http://phprimer.afmc.ca/inner/primer_contents

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Key concepts: risk factors• Risk factors for traffic-related injuries include

characteristics of:• individuals

• sex, age, ethnicity, socio-economic status

• vehicles• mass and speed

• environments (physical and social)• roadways: e.g., width, number of lanes, speed limit, volume of traffic,

etc.• urban design: e.g., mixity of land use (residential, commercial)• public policy: e.g., high-quality public transit, road safety legislation• “culture” : e.g., priority given to pedestrians v. “car culture”

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Key concepts: risk factors• Risk factors or determinants can be:• non-modifiable

• sex, age, genetic profile

• modifiable:• personal behaviours• characteristics of vehicles and the roadway environment

• Effective public health interventions should preferentially focus on modifiable factors• But, some non-modifiable factors may help orient

interventions

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Exercise: risk factors• Given the observations you made regarding potential

risk factors:

Which intersection would you expect to have a higher number of pedestrian injuries? Why?

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Key concepts: stages of prevention

Source: The Association of Faculties of Medicine of Canada (2013)http://phprimer.afmc.ca/inner/primer_contents

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Key concepts: stages of prevention• Primordial: Promoting a healthy environment in childhood which

emphasizes the importance of physical activity so that individuals, once in adulthood, are more likely to choose walking versus driving when going to work.

• Primary: Public campaigns promoting drivers to respect pedestrian right-of-way rules.

• Secondary: Prompt transportation of injured victims to a trauma center.

• Tertiary: Rehabilitation programs for victims of traffic-related injuries

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Key concepts: intervention strategies• Active interventions • rely on continued compliance from individuals in the target

population for their effectiveness• compliance may be poor because of effort, monetary

resources and/or time commitment required• therefore, may increase inequalities in health outcomes

• may be fairly simple to design and implement• e.g. school-based traffic education programs for young children

Source: The Association of Faculties of Medicine of Canada (2013)http://phprimer.afmc.ca/inner/primer_contents

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Key concepts: intervention strategies• Passive interventions• applied once, often on a population basis• often in the form of laws or regulations, thus may be difficult

to implement• once instituted, they protect the entire population,

regardless of personal characteristics• have the potential to reduce health inequalities

• e.g. installation of speed bumps on residential streets to reduce average vehicle speeds

Source: The Association of Faculties of Medicine of Canada (2013)http://phprimer.afmc.ca/inner/primer_contents

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Key concepts: the Haddon matrix• Developed by Dr. William Haddon Jr. in 1970

• Can be used to identify and categorize factors associated with injury occurrence according to:• time: pre-event, during the event, post-event• components of the epidemiologic triad

• Also useful in thinking about potential interventions• different targets (pedestrians, vehicles, environments)• multiple stages of prevention• active & passive strategies• modifiable risk factors

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Exercise: the Haddon matrix• What types of interventions did you observe? What

potential interventions did your team think of?

Take 5 minutes to classify the interventions using a Haddon matrix

  Host Agent or vector

Physical environment

Sociocultural environment

Pre-event

Event

Post-event

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