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Caltrans > District 11 > Traffic Operations > Advanced Transportation System Engineering > Smart Loop Detection System

Smart Loop Technology Demonstration Project
at Otay Mesa, San Diego

Function Overview
Otay Mesa Road Location
Vehicle classification
Preliminary Test Results
Speed Accuracy
Counting Accuracy
Tracking Capabilities

Functional overview of Smart Loop Detection System

The Link Processor is connected to Traffic Management Center (TMC) computer via telephone lines. All Link Processors transfer the information coming from IVS-2000 to the TMC computer. The TMC computer, upon receiving the vehicle data, stores the information in the database. The database calls the correlation and assignment functions to perform vehicle origin and destination matching from one loop to the next set of loops. The database starts the Graphical User Interface that runs on the 21-inch display screen.

The display is divided into three sections. The first section displays the segments located on Otay Mesa Road. The segments can be selected in order to display the visual representation of the traffic along with the average statistics that appear in the second and third sections of the display. The second section displays an animated representation of traffic with the help of vehicle icons. The lanes and sensors are drawn on the screen. The sensors can be selected to display the real-time information coming from the IVS-2000 in section three. The third section of the display has three different tables to present segment statistics, classification information, and point sensor information on Otay Mesa Road.

The display also has control buttons to start, pause, and quit the system. Current time and date are displayed. The figure below shows an example of the Otay Mesa Road user interface.

Otay Mesa Road Location of Inductive Loop Instrumentation.

To the far left is the 805 Freeway and to the far right is the Otay Mesa border crossing.

The system installed at Otay Mesa Road consists of 25 inductive loops embedded in the road. Associated with these loops are four cabinets, which house six or seven IVS-2000s that detect and classify the vehicles. The Link Processor in each cabinet collects the individual detections from each IVS-2000 and forwards the information to the Transportation Management Center (TMC) computer. The TMC computer has its own database management functions to store the incoming data. The TMC computer computes and displays the statistics and real-time information on the user interface.

Vehicle Classification

The OMR Smart Loop System currently classifies 23 different classes of vehicles, shown in Table 1, and one unknown type. Table 1 also shows the silhouettes of the 23 different classes of vehicles and their respective average lengths. Vehicle length is a function of the IVS-2000ís classification of the vehicle. An average vehicle length for each class has been determined. These same silhouettes are used on the GUI. Vehicle length is a function of the IVS-2000ís classification of the vehicle. An average vehicle length for each class has been determined.

Vehicle Classifications and Lengths

Class 1:    Motorcycle 5.6 feet
Class 2:    Passenger car 17.4 feet
Class 3:    2-axle, 4-tire single units 19.1 feet
Class 4:    Buses 41.7 feet
Class 5:    2-axle, 6-tire single units 29.0 feet
Class 6:    3-axle single units 34.0 feet
Class 7:    4+ axle single units 51.2 feet
Class 8:    4 or less axle single trailers 48.0 feet
Class 9:    5-axle single trailer trucks 62.4 feet
Class 10:   6 or more axle single trailer trucks 71.2 feet
Class 11:   5 or less axle multi trailer trucks 70.0 feet
Class 12:   6-axle multi-trailer trucks 77.5 feet
Class 13:   7 or more axle multi-trailer trucks No Data
Class 14:   Class 2 + trailer 27.4 feet
Class 15:   Class 3 + trailer 39.1 feet
Class 16:   Class 5 + trailer 44.0 feet
Class 17:   Class 6 + trailer 63.0 feet
Class 18:   Loaded auto carrier 83.1 feet
Class 19:   Empty auto carrier 80.0 feet
Class 20:   Bobtail tractor 24.0 feet
Class 21:   Combination tractor-trailer 64.4 feet
Class 22:   30-foot bus 32.4 feet
Class 23:   20-foot bus 24.0 feet

These individual vehicle classifications are grouped into Caltrans-specified categories based on the number of axles, as shown below. These categories are used for the display on the GUI.

Passenger vehicles Class :  2, 3, 14, 15
2- and 3-axle Class :  4, 5, 6, 8, 16, 20, 22, 23
4-axle Class :  7
5 or more axle Class :  9, 10, 11, 12, 13, 17, 18, 19, 21
Others Class :  1
Unknown/unclassifiable Class :  24

Speed Accuracy

The speed accuracy was tested by using a control vehicle passing through the system crossing over different sensors of different cabinets. The results of the 10 passes over the sensors are shown below.

The speed accuracy is to within 5 percent and all but one of the trials the controlled vehicle speed was faster then that of the log file, which is expected.

The Figers below shows the traffic speeds west bound during a 24 hour period. Notice how the truck traffic is about 10 mph slower then car traffic heading west bound.

Truck and passenger vehicle speed on OMR west bound using a single loop sensor. The Figers below shows the traffic speeds east bound during a 24 hour period. Again the truck traffic is 10 mph slower then the cars.

Truck and passenger vehicle speed on OMR east bound using a single loop sensor.

Counting Accuracy

The counting accuracy was based on the collected data for the classification. This was based on more than 500 test vehicles. The figure below show the counting accuracy of all the cabinets east- and west-bound.

The east-bound side of cabinet 3 was not functioning properly during our test and hence omitted. The counting accuracy for the system was above 95 percent accurate.

One can isolate the trucks from the passenger vehicle per lane over a 24 hour period as seen from the figure below. As expected the trucks and passenger vehicles count are closer together in the slow lane (lane 3) then in the other two lanes during none compute times.

Truck and passenger vehicle speed east bound isolated by lane. The total traffic for a 24-hour period on September 11 for east- and west-bound traffic.

Tracking Capabilities

The tracking test was performed using a controlled vehicle through the system on a different day than the original test. Six runs through the system were performed and, of those, two were completely tracked. Two runs were tracked for two of the three sections and on two other occasions, the controlled vehicle was tracked on only one section. On all missed track scenarios, a similar vehicle passed through the sensor during the window of classification. This window of opportunity is at a fixed time duration for the entire day and does not depend on any additional information such as traffic light information. The more information that is given to the tracker about the flow of traffic, the more accurate the estimation of the time at which the vehicle will

The figer below shows the classification of passenger vehicles (category 1) versus trucks (category 2, 3, and 4). The truck classification is above 95 percent accurate.

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