1. Technical Field
This invention relates to a speed monitoring system for an automotive vehicle, and more specifically to such a system that establishes a desired speed based on historical speed data for a particular segment of road.
2. Background
It is known to provide the driver of an automotive vehicle with a warning or advisory if the vehicle exceeds a desired maximum speed. In some systems, the desired or allowable maximum speed may be based on legally-set speed limit data stored, for example, in a digital map, or using artificial vision systems to read speed limit signs posted along the route of travel. Other proposed systems use wireless (for example radio frequency or infrared) systems to transmit signals that are received by equipment aboard the vehicle to indicate a speed limit or desired speed.
It is further known to calculate a maximum safe or recommended speed to be driven around an approaching curve and issue a warning if the vehicle exceeds (or is predicted to exceed) that speed. Such methods generally consider the road geometry, primarily the radius of curvature, to determine the recommended speed. U.S. patent application Ser. No. 12/712,446 filed Feb. 25, 2010, and assigned to the assignee of the present application, discloses such methods, and the disclosure is incorporated herein by reference. However, there are many factors other than road geometry that influence how fast a particular vehicle, as driven by a particular driver, may safely and comfortably negotiate a curve. These other factors may include a driver's particular experience level, road surface conditions, merging traffic lanes, and weather conditions.
U.S. Pat. No. 7,479,897 discloses a method of predicting an imminent vehicle rollover situation for heavy trucks driving around relatively sharp curves such as freeway exit/entrance ramps. The method includes building an accurate digital map of roadways, including a road surface bank angle and radius of curvature at each point on the roadway, using data gathered from a fleet of vehicles equipped with GPS tracking systems. A maximum safe speed is then calculated for each data point based on a calculated lateral acceleration the truck will experience when rounding a curve of that bank and curvature. The '897 reference further discusses calculating a speed distribution for each point along a roadway from data gathered by trucks that have previously driven over the road. This historical speed data is used to predict the likelihood that the truck will exceed the maximum safe speed when it reaches the up-coming curve by examining the relationship between the truck's current speed and the historical speed distribution (percentile) for its current point on the road. This method requires data-intensive measurement of road geometry in order to accurately calculate road curvature and bank angle.
Digital map data bases for use in vehicle navigation systems are well known and are evolving to contain GPS data collected by so-called probe vehicles. A probe vehicle is any vehicle equipped with appropriate GPS and related communication systems that allow the vehicle to transmit data to a remote collection point. The probe vehicles together serve as a data collection fleet. The data collected by probe vehicles may include latitude, longitude, absolute time, position error estimate, and vehicle speed. This data may be referenced to an existing map data base to permit roads to be subsequently queried to determine expected speed over a road or a segment thereof. Tele Atlas® is a digital mapping company that utilizes probe vehicle data for driving purposes. Tele Atlas® advertises that it generates speed profiles for road segments that are derived from aggregating and processing hundreds of billions of anonymous GPS measurements from millions of probe vehicles to reflect actual consumer driving patterns. This data helps determine realistic average road way speeds for different times of day and different days of the week.