Document Type

Journal Article

Publication Date


Subject Area

operations - traffic, infrastructure - vehicle, planning - signage/information, policy - fares, mode - bus


Virtual sensors, Vehicle locating systems, Travel time, Transit buses, Traffic speed, Through highways, Thoroughfares, Thorofares, Speed measurement, Real time information, Probe vehicles, Motorways, Main roads, Loop detectors, King County (Washington), Kalman filtering, Journey time, Inductive loops, Induction loops, Induction loop detectors, Freeways, Floating cars, Correlation analysis, Correlation (Mathematics), Controlled access highways, Computer graphics, Boulevards, AVL, Automatic vehicle location, Automatic location systems, Arterial streets, Arterial highways, Algorithms


New algorithms are presented that use transit vehicles as probes for determining traffic speeds and travel times along freeways and other primary arterials. A mass transit tracking system based on automatic vehicle location data and a Kalman filter used to estimate vehicle position and speed are described. A system of virtual probe sensors that measure transit vehicle speeds by using the track data is also described. Examples showing the correlation between probe data and inductance loop speed-trap data are presented. Also presented is a method that uses probe sensor data to define vehicle speed along an arbitrary roadway as a function of space and time, a speed function. This speed function is used to estimate travel time given an arbitrary starting time. Finally, a graphical application is introduced for viewing real-time speed measurements from a set of virtual sensors that can be located throughout King County, Washington, on arterials and freeways.