Travel activity may have important influences on health, potentially contributing meaningfully to both physical activity (PA; walking and cycling) and inhaled air pollution. Ubiquitous sensing technology is a promising innovation to track locations of travel activity and associated levels of energy expenditure. We present results of a pilot study testing the use and performance of Calfit, a novel smart-phone based software that continuously records geo-positioning and PA estimated from an accelerometer integrated into Android cell-phone technology. Methods: We equipped 36 volunteers with an...