In this chapter, the following terms have the meanings indicated. Terms Defined. “Agency” means: For a traffic control signal operated and maintained at an intersection under the control of the State, the law enforcement agency primarily responsible for traffic control at that intersection; or For a traffic control signal operated and maintained at an intersection under the control of a political subdivision, a law enforcement agency of the political subdivision that is authorized to issue citations for a violation of the Maryland Vehicle Law or local traffic laws or regulations. “Approach grade” means the percent grade of the roadway approaching the signal, expressed as: A positive number for an uphill grade; and A negative number for a downhill grade. “Approach speed” means the higher of the 85th percentile speed or the posted speed limit, in miles per hour (mph). “Average day” means a day representing traffic volumes normally and repeatedly found at a location, typically a weekday when volumes are influenced by employment. “Deceleration rate” means the rate, expressed in feet per second per second (ft/sec2), required to stop a motor vehicle. Where, on an average day, heavy truck traffic comprises 15 percent or less of the vehicle traffic on the approach, a value of 10.0 ft/sec2 shall be used. Where, on an average day, heavy truck traffic comprises more than 15 percent of the vehicle traffic on the approach, a value of 8.0 ft/sec2 shall be used. “Eighty fifth percentile speed” means the speed, in miles per hour (mph), at or below which 85 percent of motor vehicles travel when not slowed by a yellow or red signal indication, traffic, weather, or other conditions. “Heavy truck” means a single unit truck with three or more axles, a tractor-trailer, or a tractor-semitrailer combination. “Traffic control signal monitoring system” means a device with one or more motor vehicle sensors working in conjunction with a traffic control signal to produce recorded images of motor vehicles entering an intersection against a red signal. “Yellow change interval” means the length of time (in seconds) that a traffic control signal displays a yellow indication before changing to red.