Do provincial policies banning smoking in cars when children are present impact youth exposure to secondhand smoke in cars?

Objective: To examine youth exposure to smoking in cars following 7 provincial bans on smoking in cars with children in Canada. Method: Repeated cross-sectional data from the 2004-2012 Youth Smoking Survey (n = 91,800) were examined. Using a quasi-experimental design, contrasts of the interaction of survey year and province included in the logistic regression analyses were used to test whether exposure significantly declined pre-post implementation of a ban on smoking in cars relative to control provinces not implementing a ban. Results: Exposure across all provinces declined from 26.5% in 2004 to 18.2% of youth in 2012. Exposure declined significantly from pre to post implementation of a ban on smoking in cars with children in Ontario at time 1 post ban (Pre-Ban = 20.4% T1post = 10.3%, OR = 0.45), time 2 post ban (12.1%, OR = 0.61) and time 3 post ban (11.6%, OR = 0.58) relative to control provinces that did not implement a ban. In British Columbia exposure to smoking in cars declined significantly at pre-post ban time 3 compared to the control group (Pre-Ban = 21.2%, T3post = 9.6%, OR = 0.51). No other provinces had a significant change in exposure pre-post ban relative to the control provinces. Interpretation: Although rates declined, significant differences were only found in Ontario relative to control provinces in the immediate and long term.