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V Track: Energy-Aware Traffic Delay Estimation Using Mobile Phones

V Track: Energy-Aware Traffic Delay Estimation Using Mobile Phones. Lenin Ravindranath , Arvind Thiagarajan, Katrina LaCurts, Sivan Toledo, Jacob Eriksson, Sam Madden, Hari Balakrishnan. Massachusetts Institute of Technology. Motivation. Traffic delays and congestion Wasted fuel

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V Track: Energy-Aware Traffic Delay Estimation Using Mobile Phones

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  1. VTrack: Energy-Aware Traffic Delay Estimation Using Mobile Phones Lenin Ravindranath, Arvind Thiagarajan, Katrina LaCurts, Sivan Toledo, Jacob Eriksson, Sam Madden, Hari Balakrishnan Massachusetts Institute of Technology

  2. Motivation • Traffic delays and congestion • Wasted fuel • Commuter frustration • 4.2 billion hours in 2007 spent struck in traffic • Traffic applications • Real time traffic congestion information • Route planning - traffic aware routing • Traffic delay prediction • Estimate current delay on each road segment

  3. Vtrack Goal • Route planning • Hot spot detection Road segment delay estimates

  4. Approaches • Flow monitoring sensors • High deployment cost • GPS equipped probe vehicles • Cover large areas • Deployment cost • End user smart phones • Large penetration and massive amount of data • Sensors: GPS, Wi-Fi, GSM • On roads and time useful for other users

  5. Challenges VTrack • Wi-Fi • Infrequent GPS samples GPS Energy consumption Wi-Fi GSM 5m 50m 200m Inaccuracy of position samples

  6. Wi-Fi localization • War driving: Access point - GPS mapping • AP observations -> Centroid location • Noise • Outliers • Outages

  7. Delay estimation • Map matching • - Sequence of segments • Find delay on road segments

  8. Map matching Hidden Markov Model S2 1/3 p1 p2 S1 S1 p4 1/3 1/3 p3 S3 S2 S3 Viterbi S1 S1 S1 S1 • Noise • - Gaussian • Outliers • - Speed constraint • Outages • - Interpolation S2 S2 S2 S2 S3 S3 S3 S3 p1 p2 p3 p4

  9. Dealing with outages

  10. Delay on segments S2 p1 p2 p3 p4 p1 p2 S1 p4 S1 S1 S3 S3 p3 S3 T (S1) = t(p2) – t(p1) + ½ (t(p3) – t (p2)) T (S3) = t(p4) – t(p3) + ½ (t(p3) – t (p2))

  11. VTrack Applications • Route Planning • Shortest time path between a source and a destination • Hotspot detection • Finding road segments that are highly congested • Evaluation • Analyzed over 800 hours of drive data • 25 cars with both GPS and Wi-Fi

  12. Key Results • HMM based map matching is robust to noise • Trajectories with median error less than 10% • Delay estimates from Wi-Fi are accurate enough for route planning • Though individual segment delay estimates have 25% median error • Over 90% of shortest paths have travel times within 15% of true shortest path • Accurately detect over 80% hotspots with less than 5% false positives

  13. Further work • Sampling GPS infrequently • Improves the accuracy of Wi-Fi based estimates • Analyzed energy consumption • Adaptive sampling • Dynamically selects best sensor • Based on road networks, accuracy, energy • Segment delay prediction

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