The SMFS identified the location of the vehicle (via global positioning system information) and
corresponding posted speed limit of the road segment on which the vehicle was traveling. The
SMFS provided information to the driver about the current posted speed limit, when available, via a
display. When the SMFS determined the vehicle exceeded the speed limit (by a predefined
threshold) there was visual and auditory feedback. A mild auditory warning (a single beep) was given
when the posted speed limit was exceeded by 2 mph and a stronger auditory warnings (a verbal
message and 1-second buzzer) were given at a higher speed threshold (e.g., 10 mph over the posted
speed limit). A third, even stronger warning was issued at speeds over 80 mph (a verbal message and
a longer buzzer). For the mild speed warning the single beep only occurred one time when the
vehicle remained within the speed tolerance zone and the speed limit did not change. The mild
speed warning gave participants speed awareness information within a speed tolerance zone. There
were occasions when participants’ speed often varied above and below the mild speed tolerance
zone. In these situations where speed may have wavered above and below the 2 mph threshold, the
warning would not occur more than once every 5 minutes. For the stronger speed warning the
frequency of the auditory feedback was given 10 seconds after the initial warning and again 20
seconds after that if the speed had not been reduced below the warning threshold. If teens
continued to speed, the warning threshold would reset after 5 minutes. The strongest warning issued
at speeds over 80 mph included a speech warning and a long buzz sound. These levels were also
affected by the other subsystems such that if thresholds were exceeded in allied subsystems (e.g.,
SBDRS or PPS) the warning thresholds used as the basis to provide SMFS-related feedback
decreased and therefore feedback and vehicle adaptations occurred sooner.
8
An ideal implementation could visually display advisory limits (e.g., curve warnings) in addition to
regulatory speed limits. Updated travel information based on GPS coordinates could display realtime
information for drivers such as active work zones and school zone warnings. An ideal
implementation would also incorporate inputs from the context subsystem and could provide
warnings to the driver based on environmental conditions and recommended speeds.
The demonstration and FOT vehicle implementation displayed speed information, when available,
through visual icons presented on their respective displays. The mild and strong auditory warnings
were also implemented and provided drivers with feedback when they had exceeded the
predetermined speed limit threshold. The SMFS also fed into the adaptive nature of the STC and the
other subsystems. For example, if teens violated the speed thresholds this in turn would reduce the
warnings thresholds for the Excessive Maneuver subsystem, resulting in increased sensitivity for
excessive maneuvers. The impact of other subsystems on the feedback provided by the SMFS and
the adaptive attributes of the system are shown in Table 2-1. As the number of cautionary inputs
increased the point at which the teen would receive feedback was sooner. The feedback from the
SMFS follows closely with prior work from intelligent speed adaptation systems (ISA), where speed
reduction was identified based on a number of levels presented to a driver (Brookhuis & de Waard,
1999).