title: Identifying Active Travel Behaviors in Challenging Environments Using GPS, Accelerometers, and Machine Learning Algorithms.
abstract: BACKGROUND
  Active travel is an important area in physical activity research, but objective measurement of active travel is still difficult. Automated methods to measure travel behaviors will improve research in this area. In this paper, we present a supervised machine learning method for transportation mode prediction from global positioning system (GPS) and accelerometer data.
  
  
  METHODS
  We collected a dataset of about 150 h of GPS and accelerometer data from two research assistants following a protocol of prescribed trips consisting of five activities: bicycling, riding in a vehicle, walking, sitting, and standing. We extracted 49 features from 1-min windows of this data. We compared the performance of several machine learning algorithms and chose a random forest algorithm to classify the transportation mode. We used a moving average output filter to smooth the output predictions over time.
  
  
  RESULTS
  The random forest algorithm achieved 89.8% cross-validated accuracy on this dataset. Adding the moving average filter to smooth output predictions increased the cross-validated accuracy to 91.9%.
  
  
  CONCLUSIONS
  Machine learning methods are a viable approach for automating measurement of active travel, particularly for measuring travel activities that traditional accelerometer data processing methods misclassify, such as bicycling and vehicle travel.
authors.affiliation: Department of Electrical and Computer Engineering, University of California San Diego , La Jolla, CA , USA.
authors.forename: Katherine
authors.initials: K
authors.lastname: Ellis
authors.affiliation: Department of Family and Preventive Medicine, University of California San Diego , La Jolla, CA , USA.
authors.forename: Suneeta
authors.initials: S
authors.lastname: Godbole
authors.affiliation: Department of Family and Preventive Medicine, University of California San Diego , La Jolla, CA , USA.
authors.forename: Simon
authors.initials: S
authors.lastname: Marshall
authors.affiliation: Department of Electrical and Computer Engineering, University of California San Diego , La Jolla, CA , USA.
authors.forename: Gert
authors.initials: G
authors.lastname: Lanckriet
authors.affiliation: Department of Mathematics and Statistics, University of Massachusetts Amherst , Amherst, MA , USA.
authors.forename: John
authors.initials: J
authors.lastname: Staudenmayer
authors.affiliation: Department of Family and Preventive Medicine, University of California San Diego , La Jolla, CA , USA.
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Kerr
keywords: physical activity; random forest