The SmarTek Acoustic Sensor-Version 1 (SAS-1) is comprised of an array of rugged microphones for converting impinging acoustic signal wave fronts to analog signals, analog signal conditioning and sampling circuitry to condition and digitize the microphone signals, and a programmable state of the art Digital Signal Processor (DSP) with associated memory and communication circuitry to implement specific signal processing, spatial processing, and vehicle detection algorithms. The SAS-1 "listens to" and processes every received acoustic signal generated by passing vehicles or stationary (idling) vehicles. SAS-1 uses SmarTek Systems advanced signal processing technology to perform signal frequency component discrimination and advanced adaptive spatial processing to create multiple acoustic signal arrival direction (look directions) channels. SAS-1 then determines the arrival direction of each acoustic signal it receives and correlates each signal arrival direction with the highway lanes associated with the installation site. Detection and traffic flow information are assigned to the appropriate lane being monitored.

The SAS-1 provides effective and accurate vehicle presence detection and associated traffic flow measures on a lane by lane basis. The SAS-1 detects vehicles passing the sensor station at any reasonable (and allowable) speed from stop and go to free flow. There is no inherent upper speed limitation relative to highway traffic since faster moving vehicles create increased levels of acoustic energy making them easier to detect. The SAS-1 will not tune out a vehicle that remains in the detection zone for a prolonged period of time.

Because the SAS-1 is based on passive acoustic detection of motor vehicles, there is virtually no loss of detection performance due to variation in weather or environmental conditions or visibility conditions.

The number of lanes monitored by the SAS-1 is set at 5 as a default (for example, 3 lanes and 2 shoulders as shown here). This limit is driven by constraints for a typical side mount geometry (occlusion of the far lanes).

The SAS-1 provides a detection zone equivalent to that of a 6 foot loop in the direction of traffic flow (up/down road) and a completely selectable zone size in the cross road direction (less than 6 feet to an entire lane width or even multiple lane widths). This capability is very useful for exit and entry ramp situations where vehicles routinely travel to one side or the other missing loop detectors entirely. With the SAS-1, a detection zone can be selected which covers the entire lane width including some or all of the shoulders.

The SAS-1 provides for several different interfaces depending on the communication link and the cabinet controller interface desired. The standard SAS-1 output message provides traffic flow measurements of vehicle volume, lane occupancy, and average speed for each monitored zone (3 lanes and 2 shoulders) for a specified update period (i.e., 20 sec, 30 sec, 1 min, etc.). Vehicle presence relays are available via an optional SAS-1 Bit Serial to Parallel Interface in the roadside cabinet. The SAS-1 supports the following electrical communication interfaces:

The SAS-1 re-regulates the supply voltage thus compensating for voltage drops and fluctuations caused by long home run cables:

1) Supply Voltage at the Sensor..................12 to 24 VDC
2) Required Power..........................................1.5 watts

The SAS-1 is a very compact multi-lane highway monitoring sensor. Superior spatial resolution is achieved by advanced processing rather than physical aperture, thereby resulting in a very small sensor footprint, as described here:

1) Dimensions.................................12 inches long x 8 inches wide x 5 inches deep
2) Weight.........................................Less than 4.5 lbs., less than 7 lbs. w/recommended mounting hardware
3) Material/Finish............................Aluminum/Enamel/Stainless Steel Fasteners
4) Mounting Approach...................2 inch Diameter Aluminum Tube/Stainless Steel Bands
5) Operating Temperature..............-20 Deg C to 75 Deg C
6) Humidity.......................................5% to 100%
7) Shock............................................NEMA TS2-2.1.10
8) Vibration.......................................NEMA TS2-2.1.9

The SAS-1 provides a great deal of flexibility relative to installation. Its compact size and modest weight make installation easy for a single installer using a bucket truck. Off the shelf, low cost mounting brackets can be utilized. Mounting brackets should allow for coarse mechanical positioning so that the sensor face is pointing toward the center of the lanes to be monitored. Place the sensor’s long dimension in the up/down road direction and the sensor’s short dimension in the cross road direction. Powering the sensor and using the SAS-1 Monitor and Setup program on a PC Laptop makes the SAS-1 installation and pointing easy and quick. Monitoring the real time display while mechanically orienting the sensor removes any guesswork relative to the SAS-1installation. After the SAS-1 is mechanically oriented and locked down, the position and size of each detection zone (up to 5 in cross road direction) can then be electronically adjusted using the SAS-1 Monitor and Setup program to precisely match the highway lanes and the specific traffic flow situation.