A major concern of drivers in winter is the current road condition. Taxis, which move ceaselessly around a wide area, have great potential as sensors for detecting road-surface conditions in a given area. To establish a method with which to estimate road conditions based on the vehicular motion of taxis, field experiments were conducted by using probe vehicles fitted with vehicular-motion sensors and a Global Positioning System device, before implementation in taxis. Preliminary analyses were performed by using data measured on a test track, urban streets, and an expressway. The slip ratio, defined as the relative difference in speed between vehicle and tire wheel, was effective in indicating how slippery the road surfaces were. Taxi vehicular-motion data were collected for more than 1 month, although unlike with probe vehicles, the wheel speed was not measured. Some features of vehicular motion specific to slippery roads were identified, and the discriminability of road conditions, whether icy or dry, without the use of wheel-speed data, was examined.
Samenvatting