Method for creating speed profiles for digital maps
Probe data collected at times of low traffic density is analyzed to derive a Raw Road Design Speed Limit (RRDSL, 16 ) for each road segment or group of segments in a digital map. The RRDSL ( 16 ), comprised of longitudinally distributed speeds, is associated with the road segment and stored in a digital medium to indicate the limits of the road section in free flow traffic. The longitudinally distributed speeds may be limited by local speed limits or other business logic to establish a Legal Raw Road Design Speed Limit (LRRDSL, 17 ). Either the RRDSL ( 16 ) or the LRRDSL ( 17 ) can be further modified to smooth acceleration and deceleration rates between changes in the longitudinally distributed speeds to create an Optimal Longitudinal Speed Profile (OLSP, 18 ), which represents optimized energy consumption. A signal can be produced if a driver's current speed rises unacceptably above a longitudinally distributed speed in real time. The signal can be audible, visible and/or haptic. Real-time traffic density information can be inferred by comparing current speed data to the longitudinally distributed speed for that position. If the current speed is consistently lower than the longitudinally distributed speed for that position, an inference is drawn that the road section is inefficient. Road efficiency assessments can be transmitted to a service center and/or other vehicles, and used by navigation software.
1. A method, comprising:
collecting probe data from a plurality of probes traversing a multi-lane road segment in the form of vehicular traffic flow, each probe developing a respective probe trace comprising a sequence of discrete time-stamped probe positions and having sufficient resolution to identify particular lanes traversed in the road segment;
identifying a time span for the road segment with free flow traffic conditions;
selecting, by a processor, probe data for the road segment collected during the identified time span;
statistically deriving, by the processor, longitudinally distributed average speeds at positions along the road segment from the selected probe data, the longitudinally distributed average speeds being representative of a free flow speed of vehicular traffic flow along the road segment and velocity variations along a length of the road segment;
generating, from the longitudinally distributed average speeds, an Optimal Longitudinal Speed Profile (OLSP), the OLSP being a separate speed profile that includes speeds based on the longitudinally distributed average speeds, but with smoothed transitions for accelerations and decelerations in the longitudinally distributed average speeds that improve energy efficiency with respect to the longitudinally distributed average speeds;
associating, by the processor, the longitudinally distributed average speeds and the OLSP with the road segment; and
storing the longitudinally distributed average speeds and the OLSP in a digital medium, the storing comprising storing unique longitudinally distributed average speeds for each lane in the road segment.
2. The method of claim 1 further including the step of providing a digital map having at least one link corresponding to the road segment; and said step of storing the longitudinally distributed average speeds includes augmenting the digital map with a data layer containing the stored longitudinally distributed average speeds.
3. The method of claim 1 further including the step of creating a Legal Raw Road Design Speed Limit (LRRDSL) by limiting the longitudinally distributed average speeds with at least one predetermined threshold.
4. The method of claim 3 wherein said step of creating a Legal Raw Road Design Speed limit (LRRDSL) includes using the established speed limit of the road segment as the predetermined threshold.
5. The method of claim 3 wherein the LRRDSL includes an artificial maximum threshold based on fuel economy statistics.
6. The method of claim 1 wherein said step of creating an OLSP includes creating the OLSP on the fly in an in-vehicle application.
7. The method according to claim 1 further including adjusting the longitudinally distributed average speeds on the basis of at least one vehicle specific parameter.
8. The method according to claim 1 , wherein the OLSP is derived from kinetic energy simulations for a plurality of vehicle types or categories.
9. The method of claim 1 further comprising using the longitudinally distributed average speeds to advise a driver.
10. The method of claim 1 further comprising enhancing the OLSP using a dynamic real time parameter or coefficient.
11. A navigation device configured to be carried in a vehicle, comprising:
a position reading device configured to determine the current longitudinal position and speed of a navigation device along a multi-lane road segment, the position reading device having sufficient resolution to identify particular lanes traversed in the road segment; and
a digital storage medium comprising a digital map having a plurality of links corresponding to road segments traversable by the navigation device, the digital map having a data layer comprising longitudinally distributed average speeds representative of the fastest or free flow speed of vehicular traffic flow at a plurality of positions along each road segment and velocity variations along a length each road segment and an Optimal Longitudinal Speed Profile (OLSP), the OLSP being a separate speed profile for each road segment that includes speeds based on corresponding longitudinally distributed average speeds, but with smoothed transitions for accelerations and decelerations in the corresponding longitudinally distributed average speeds that improve energy efficiency with respect to the corresponding longitudinally distributed average speeds, the stored longitudinally distributed average speeds comprising unique longitudinally distributed average speeds for each lane in the road segment;
the navigation device being configured to compare the determined current speed to a speed derived from the longitudinally distributed average speeds for: (i) the determined current position; or (ii) a position ahead of the determined current position, and to produce a sensory signal when the determined current speed exceeds the speed derived from the longitudinally distributed average speeds by a predetermined value.
12. The navigation device according to claim 11 , wherein the sensory signal includes at least one of: an image on a display screen; an audible sound; and a haptic feedback.
13. The navigation device according to claim 11 , wherein the navigation device is configured to communicate with an ADAS application of the vehicle that acts to actively conform the current speed to a speed derived from the longitudinally distributed average speeds.
14. The navigation device according to claim 11 , wherein the longitudinally distributed average speeds for a road segment are statically derived from a plurality of probes traversing the road segment in the form of vehicular traffic flow, each probe developing a respective probe trace comprising a sequence of discrete time-stamped prove positions.
15. The navigation device according to claim 11 , wherein the speed derived from the longitudinally distributed average speeds is determined on the basis of at least one dynamic real time parameter.
16. The navigation device according to claim 11 , wherein the speed derived from the longitudinally distributed average speeds is determined on the basis of at least one vehicle specific parameter.
17. The navigation device according to claim 11 , wherein the speed derived from the longitudinally distributed average speeds includes lane specific data related to a direction of travel along the road segment.
18. The navigation device according to claim 11 , wherein the determination of when to produce the sensory signal additionally uses dynamic environmental factors.
19. The navigation device according to claim 11 , wherein the longitudinally distributed average speeds are attributed to the road segment as one of: a parametric curve in view of a function of distance, a set of discrete optimal speeds between which to linearly interpolate, or normalized variations above and below a legal speed limit or artificial threshold.
20. A non-transitory computer-readable medium which stores a set of instructions which when executed performs a method comprising:
collecting probe data from a plurality of probes traversing a multi-lane road segment in the form of vehicular traffic flow, each probe developing a respective probe trace comprising a sequence of discrete time-stamped probe positions and having sufficient resolution to identify particular lanes traversed in the road segment;
identifying a time span for the road segment with free flow traffic conditions;
selecting probe data for the road segment collected during the identified time span;
statistically deriving longitudinally distributed average speeds at positions along the road segment from the selected probe data, the longitudinally distributed average speeds being representative of a free flow speed of vehicular traffic flow along the road segment and velocity variations along a length of the road segment;
generating, from the longitudinally distributed average speeds, an Optimal Longitudinal Speed Profile (OLSP), the OLSP being a separate speed profile that includes speeds based on the longitudinally distributed average speeds, but with smoothed transitions for accelerations and decelerations in the longitudinally distributed average speeds that improve energy efficiency with respect to the longitudinally distributed average speeds;
associating, by the processor, the longitudinally distributed average speeds and the OLSP with the road segment; and
storing the longitudinally distributed average speeds and the OLSP in a digital medium, the storing comprising storing unique longitudinally distributed average speeds for each lane in the road segment.