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Development of A Loop Detector Simulator (LOOPSIM
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1. respectively Please note that the status of one loop detector is recorded in one bit One byte contains the statuses of eight loop detectors at a particular moment sixteen channels are therefore recorded in two bytes each byte is shown as a number range from 0 to 255 In Figure 6 a the SENDI curve represents the status of loops 1 through 8 and the SEND2 curve represents the status of loops 9 through 16 sent by LOOPSIM Correspondingly in figure 6 b curve shows the received status of loops 1 through 8 and the RECV2 curve denotes the received status of loops 9 through 16 The time interval between any two consecutive points is approximately 16 7 ms Comparison between the corresponding curves did not find any differences except the consistent system delay of about 16 ms This test supports the conclusion from the first test 1 LOOPSIM performed superbly at 60 Hz with guaranteed accuracy and sequential order of the test data set Cheevarunothai Wang and Nihan 11 CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE IMPROVEMENT Inductance loops are the most widely deployed traffic sensors in the existing road infrastructure They are a major data source for Advanced Traveler Information Systems ATIS and Advanced Traffic Management Systems ATMS Most actuated intersection signal control systems and freeway monitoring systems use loop detectors for vehicle detection e g adaptive signal control systems and ramp metering sys
2. and Nihan 3 unavailability of live loop detector outputs obstructs educators from reaching their purpose Installation of physical loop detectors in teaching areas may be impossible because of their cost and space requirements The Controller Interface Device CID developed by the National Institutes of Advanced Transportation Technology NIATT provides a data exchange interface between computers running simulation software and traffic controllers so that signal timing plans can be tested with controller hardware in a laboratory before being deployed in the field 4 7 The CIDs have enabled Hardware In The Loop Simulations HITLS and made traffic simulation results more reliable However CIDs are not designed for simulating loop event data for in laboratory research and education The frequency of providing loop event data from a CID depends on the microscopic simulation software that drives it Typically a microscopic simulation software package has a deterministic frequency of recalculating the position of each vehicle between 1 and 10 HZ 5 This limits the time resolution of loop event data to 0 1 to 1 second which is much lower than the 0 0167 second resolution level for most loop detection systems Additionally using a CID for loop event data simulation requires purchasing both simulation software and a CID This can easily cost around 3 000 Therefore a loop detector simulator that can generate precise real time live loop inputs to contr
3. 4 Loop Detectors Layout for the Vehicle Arrival Pattern Simulations Test Figure 5 Histograms of Sent Data and Received Data in the Vehicle Arrival Pattern Simulations Test a Histogram of Data Generated and Sent by LOOPSIM b Histogram of Data Received by the DEDAC System Figure 6 Curves of Sent and Received Data in the Roadway Traffic Emulations Test a Field Recorded Event Data Sent by LOOPSIM b Event Data Received by the DEDAC System during the Test Cheevarunothai Wang and Nihan 16 Figure 1 Components of an Inductive Loop Detector Field Component Toop Delechors Typical Traffic Control Cabinet Cheevarunothai Wang and Nihan 17 Figure 2 Connection Diagram of LOOPSIM Components 332 Control Cabinet Digital LOOPSIM Program Card Reed Relays 170 Controller DEUs Input File Cheevarunothai Wang and Nihan 18 Figure 3 A Snapshot of LOOPSIM s Main User Interface File Help Channel Connection Tests Roadway Traffic Emulations m rm 1 go Channel Connection Select Input Data C DEDAC 5 6 7 8 C Vehicle Anival iC rs Ceo Cen re Frequency 60 ae C Emulatons 54 Fes Reset On Vehicle Pattern Arrival Simulations Traffic Flow Vehicles Hour Uniform Distibuson 1 500 2 500 3 eoo 24 eoo 700 se 700 s7 800 2 s00 900 10 900 111000 12 1000 13 1100 14 1100 15 1200 z16 1
4. Lyddy and A Sabardonis The Berkeley Highway Laboratory Building on the I 880 Field Experiment Proc IEEE ITS Council Annual Meeting IEEE 2000 pp 5 10 Zhang X Y Wang N L Nihan and M E Hallenbeck Development of A System to Collect Loop Detector Event Individual Vehicle Data In Transportation Research Record Journal of the Transportation Research Board No 1855 TRB National Research Council Washington D C 2003 pp 168 175 NIATT National Institute for Advanced Transportation Technology Tech Brief A Publication of the National Institute for Advanced Transportation Technology University of Idaho October 2002 lt http www webs1 uidaho edu niatt publications Tech_Brief Oct02 pdf gt Accessed on July 25 2004 NIATT National Institute for Advanced Transportation Technology Controller Interface Device CID II Final Report for Office of University Research and Education U S Department of Transportation NIATT National Institute for Advanced Transportation Technology University of Idaho November 2001 http ntl bts gov lib 19000 19100 19165 PB2002104697 pdf Accessed on July 25 2004 Bullock D B Johnson R B Wells M Kyte and Z Li Hardware In The Loop Simulation Transportation Research Part C 12 2004 pp 73 89 Engelbrecht R J K N Balke S P Venglar R S Sunkari Recent Applications of Hardware In The Loop Traffic Simulation Institute of Trasportation Engineers Meeting
5. event timing Multimedia timer services allow applications to schedule timer events with the greatest resolution or accuracy possible for the hardware platform It runs on its own thread and moves among threads to handle the raised elapsed event resulting in greater accuracy than other timers in raising the event on time Its resolution on the hardware platform tested can accurately support simulation at up to 90 Hz The multithreading program technique was used to control parallel tasks in LOOPSIM Of the three ports with the PC CARD D24 CTR3 card two ports sixteen channels were programmed as output channels and can send signals out simultaneously at a high frequency 60 Hz or higher This makes LOOPSIM capable of simulating sixteen inductance loops simultaneously Since loop detectors work independently each channel is managed by one independent thread in LOOPSIM Since the typical voltage output from computer ports are between O volts and 5 volts an external power supply of 12 volts is needed for simulating the off status of an inductive loop We recommend using the Input File of the Model 332 cabinet as the external power supply for high voltage signals A mechanical relay is used to switch between the high voltage from the Input File when simulating the off status and the low voltage from the PC CARD D24 CTR3 card when simulating the status for each channel The compact SPST reed relay drivable with the PC CARD D24 CTR3 car
6. or connection failures The DEU output voltage is low under the open loop status However if a DEU is unplugged from the cabinet its corresponding output channels in the Input File will remain at high voltage that indicates no physical loops are connected to the channels This feature is standard for all Model 332 cabinets and we use the high voltage of the Input File as the external power supply for high voltage output of LOOPSIM In the Model 332 cabinet the DEU output signals are available for the Type 170 controller to poll at the Input File As shown in Figure 2 LOOPSIM 1 placed between the Input File and the Type 170 controller of the controller cabinet Such a connection does not require any further wiring change in the cabinet When LOOPSIM simulates a call or the status it simply cuts the Input File out of the circuits and sends a low voltage signal to the controller If the off status is simulated LOOPSIM cuts itself out of the circuit with mechanical relays to make the controller directly connect to the Input File whose voltage stays at 12 volts Cheevarunothai Wang and Nihan 5 Specifically LOOPSIM is designed to contain the following five components e LOOPSIM Software The main function of the LOOPSIM software is to control the digital Input Output card according to the users objective It has been developed in C language e laptop computer with a Personal Computer Memory Card International Associatio
7. the ability to control the test input LOOPSIM can be used to test the performance of real time traffic applications For example before a new speed estimation algorithm using single loop outputs is deployed it must be tested preferably using field recorded loop event data With the roadway traffic emulations feature this test can be easily conducted Suppose we have several loop event data sets collected by the DEDAC system from inductive loop stations on I 5 To test the new speed estimation algorithm implemented in a Type 170 compatible controller we can simply select the most appropriate data set and use LOOPSIM to replay this previously recorded data set to recreate the true traffic situation at the time the data was recorded Since the ground truth event data are known evaluation of the algorithm s performance becomes much easier and compelling Next version of LOOPSIM will have a feedback function from the controller to the laptop computer With the feedback function LOOPSIM will be more powerful For example LOOPSIM will have capability to test the performance of adaptive signal control algorithms in laboratory SYSTEM TESTING The reliability and accuracy of LOOPSIM was evaluated in the STAR Lab at the University of Washington The evaluation was conducted through two types of tests 1 connection tests and 2 performance amp accuracy tests Cheevarunothai Wang and Nihan 9 Connection Tests Connection tests are required b
8. 200 Speed Miles Hour Erlang Distribution 2 eo 3 eo eo 5 60 ssf 60 7 60 sf 60 C Normal Distribution 29 60 10 60 11 60 12 60 13 60 14 60 15 60 16 60 _ Cheevarunothai Wang and Nihan 19 Figure 4 Loop Detectors Layout for the Vehicle Arrival Pattern Simulations Test Lane 4 S LJ Lane 5 8 19 015 Cheevarunothai Wang and Nihan 20 Figure 5 Histograms of Sent Data and Received Data in the Vehicle Arrival Pattern Simulations Test a Histogram of Data Generated and Sent by LOOPSIM Scan Count 450 400 350 300 250 200 150 100 50 0 Note SENDC Scan Court Car generated by LOOPSIM from Input Speed sending at 60 Hz SENDHW Headways between Vehicles calculating from Input Flow generated by LOOPSIM scanned at 60 Hz b Histogram of Data Received by the DEDAC System 12 13 14 15 16 Note Scan Count Car recorded by DEDAC system ai 60 Hz RECVHW Headways between Vehicles recorded by DE DAC system Scanned at 60 Hz Cheevarunothai Wang and Nihan Figure 6 Curves of Sent and Received Data in the Roadway Traffic Emulations Test a Field Recorded Event Data Sent by LOOPSIM Binary Output 122 243 364 48 606 727 848 969 1090 1211 1332 1453 1574 1695 1816 1937 Time Millisecond Note SENDI Field Binary Traffic Event Data for Loop Number 1 to 8 sent by LOOPSIM at 60 Hz SEND2 Field Binary Traffic
9. Draft Development of A Loop Detector Simulator LOOPSIM for In Laboratory Traffic Research and Education Patikhom Cheevarunothai Graduate Research Assistant Department of Civil amp Environmental Engineering University of Washington seattle WA 98195 2700 Tel 206 335 2516 Fax 206 543 5965 Email num Q u washington edu Yinhai Wang Assistant Professor Department of Civil amp Environmental Engineering University of Washington Seattle WA 98195 2700 Tel 206 616 2696 Fax 206 543 5965 Email yinhai Qu washington edu Nancy L Nihan Professor and Director Transportation Northwest TransNow Department of Civil amp Environmental Engineering University of Washington Seattle WA 98195 2700 Tel 206 543 9639 Fax 206 543 5965 Email nihan u washington edu Submission Date March 20 2006 Cheevarunothai Wang and Nihan 1 Abstract This paper describes a LOOP detector SIMulator LOOPSIM system designed for traffic research and education LOOPSIM is capable of simulating calls from loop detectors and testing algorithms executable in the controller It can also be used to simulate different patterns of traffic streams and replay collected loop event data With the aid of LOOPSIM researchers and educators can designate traffic characteristics in line with the purpose of the testing or teaching Keywords LOOPSIM inductance loop detectors traffic control system freeway and intersection applic
10. Event Data for Loop Number 9 io 16 sent by LOOPSIM at 60 Hz b Event Data Received by the DEDAC System during the Test Binary Output 123 245 36 7 489 611 733 855 977 1099 1221 1343 1465 1587 1700 1831 1953 Time Villisecond Note Binary Traffic Event Data for Loop Number 1 8 received by DE DAC at 60 Hz RECV2 Binary Traffic Event Data for Loop Number 9 io 16 received by DEDAC at 60 Hz 21
11. and Exhibit 2000 Compendium of papers pp 14 RENO A amp E 2004 Website http www renoae com Documentation G Released 2229620 8 277 98 pdf Accessed on July 25 2004 Sealevel Systems Inc 2004 Model PC CARD D24 CTR3 User Manual File lt http measurementcomputing com PDFManuals pc card d24 ctr3 pdf Accessed on July 18 2004 10 Cheevarunothai P Y Wang and N L Nihan Development of Advanced Loop Event Analyzer ALEDA th for Investigations of Dual Loop Detector Malfunctions In The 12 World Congress on Intelligent Transportation Systems San Francisco 2005 Cheevarunothai Wang and Nihan 14 11 Microsoft Developer Network Library MSDN lt http www msdn microsoft com library gt Accessed on July 1 2004 12 Clark D C W T Scherer and L Smith Performance Cost Evaluation Methodology for ITS Equipment Deployment Research report for the Center for ITS Implementation Research 2000 http www paragoncom convITS papers3 corsim htm Toc482685636 Accessed on July 29 2004 13 Wang Y and L N Nihan Can Single Loop Detectors Do the Work of Dual Loop Detectors ASCE Journal of Transportation Engineering 129 2 2003 pp 169 176 Cheevarunothai Wang and Nihan 15 Lists of Figures and Tables Figure 1 Components of an Inductive Loop Detector Figure 2 Connection Diagram of LOOPSIM Components Figure 3 A Snapshot of LOOPSIM s Main User Interface Figure
12. and accurate LOOPSIM contains three major features channel connection tests vehicle arrival pattern simulations and roadway traffic emulations These features enable a variety of system tests in laboratories at a low cost and make performance evaluations more accurate We will continue to improve LOOPSIM by adding more simulation features and testing it with different hardware settings including other types of controllers and cabinets We are currently working on the feedback function from the controller to the laptop computer Next version LOOPSIM will be more powerful with such a new function We believe that there is a great potential to use LOOPSIM for advanced traffic research and education Cheevarunothai Wang and Nihan 12 ACKNOWLEDGEMENTS The authors express their deep appreciation to Mr Bryan Bailey at Washington State Department of Transportation and Mr Mike Whiteaker at the City of Bellevue Department of Transportation for providing test devices used in this study The authors are also grateful for the financial support to the STAR Lab from TransNow USDOT University Transportation Center Federal Region 10 and Department of Civil and Environmental Engineering at the University of Washington Cheevarunothai Wang and Nihan 13 REFERENCES 1 2 3 4 5 6 7 8 9 ITE Institute of Transportation Engineers Traffic Detector Handbook 2 Edition Washington D C 1997 Coifman B D
13. ations in laboratory testing and teaching Cheevarunothai Wang and Nihan p INTRODUCTION Inductance loop detectors are the most popular form of detection systems and have been most widely deployed in the existing road infrastructure 1 They are a major data source for Advanced Traveler Information Systems ATIS and Advanced Traffic Management Systems ATMS Most actuated intersection signal control systems and freeway monitoring systems use loop detectors for vehicle detection Loop detectors may be deployed as single loops to measure traffic volume and lane occupancy or dual loops to collect speed and vehicle length data in addition to the single loop measurements An inductance loop detector contains two parts a field component and a Detector Electronics Unit DEU The field component consists of one or more turns of insulated loop wire wound in a shallow slot sawed into the pavement a pull box at curbside and a lead in cable that connects the pull box and the DEU The DEU 1s housed in controller cabinet Figure 1 shows the components of an inductance loop detector system Each loop detector is a tuned electrical circuit of which the loop wire is the inductive element When a vehicle drives over the loop wire eddy currents are induced around the peripheral metal of the vehicle Although the iron mass of the vehicle s engine transmission or differential will increase the loop inductance due to the ferromagnetic effect the decrease in
14. d was selected in our implementation of LOOPSIM to conduct this function Cheevarunothai Wang and Nihan 7 System Features The main user interface of LOOPSIM is shown in Figure 3 It contains components that support channel connection tests vehicle arrival pattern simulations and roadway traffic emulation features Channel Connection Tests The main purpose of the channel connection tests is to check the operation of every channel before actual testing and teaching It is recommended that users check the status of every channel using this feature before using other LOOPSIM features Before conducting the channel connection tests a user needs to choose which channels to test by selecting the check boxes of channels listed on the main user interface Then pushing the ON button will cause each checked channel to switch to the low voltage status Remember that low voltage represents the on status of the virtual loop to the controller After the ON button is clicked it becomes the OFF button Once the OFF button is clicked the channel connection tests terminate and the channels switch back to high voltage status Vehicle Arrival Pattern Simulations Vehicle arrival patterns are important parameters for many simulation applications The CORridor SIMulation CORSIM package developed through the Federal Highway Administration FHWA uses a uniform distribution as the default arrival pattern for entry node vehicle gen
15. efore LOOPSIM is used to conduct more complicated tests or teaching As the first step of the LOOPSIM evaluation connection tests were preformed to ensure that LOOPSIM could work together with the available traffic control devices including the Model 332 cabinet and the Type 170 controller LOOPSIM was connected between the Type 170 controller and the Input File of the Model 332 cabinet This connection follows exactly the design of LOOPSIM as specified in Figure 2 The connections for the sixteen output channels of LOOPSIM were tested individually to ensure that they were properly connected Then random combinations of the output channels were tested to make sure that channels did not interfere with each other These tests were accomplished with the channel connection tests feature of LOOPSIM A multi meter was used to measure the voltage of signals feeding the Type 170 controller The voltage corresponding to the simulated status was verified to be very close to 0 volts and the voltage in response to the simulated off status was found to be approximately 12 volts Additionally we used the DEDAC system to record the outputs of each virtual loop detector the simulated on and off statuses were successfully captured by the DEDAC system These test results concluded that the design of LOOPSIM was reasonable and that all sixteen output channels were successfully connected and worked independently Performance amp Accuracy T
16. eration CORSIM has also made two other arrival distributions normal and Erlang available to model random arrivals 12 Many traffic control and assignment algorithms are also based on certain assumptions of vehicle arrival patterns To facilitate the test of such algorithms three vehicle arrival distributions were implemented uniform normal and Erlang A user can click to select the desired vehicle arrival pattern for the test and LOOPSIM will create a loop event data sequence that follows the designated distribution for the controller to read Cheevarunothai Wang and Nihan g Here we use the example of uniform arrival pattern to illustrate how to use this feature A user needs to specify the hourly traffic volume and average speed in mph for each lane on the LOOPSIM interface These parameters will be used to calculate the time headways between consecutive vehicles and the scan counts for each vehicle based on the vehicle length distribution observed by Wang and Nihan 13 Roadway Traffic Emulations This feature allows the recreation of true traffic situations for in laboratory test and teaching There are two advantages to this feature 1 we can control test input to satisfy the specific purpose of a test or teaching by choosing the right data set recorded at the right time and location and 2 a chosen data set can be used as ground truth data for evaluating the performance of systems or estimation models being tested Because of
17. ests This set of tests was conducted to evaluate the performance and accuracy of LOOPSIM when using the vehicle arrival pattern simulations and the roadway traffic emulation features Performance refers to whether loop event data can be simulated at the desired frequency without significant delays Accuracy indicates whether a simulated event data sequence is preserved at the controller input side Without changing the connections set up in the connection tests we conducted two more tests one for the vehicle arrival pattern simulations feature only uniform distribution was tested and the other for the roadway traffic emulation feature The results for both tests can be easily verified by comparing the original data file in LOOPSIM with the received data file by the DEDAC system The only difference between these two tests was that the original data file for testing the feature of vehicle arrival pattern simulations was generated by LOOPSIM based on a uniform distribution of vehicle arrival times and the observed vehicle length distribution by Wang and Nihan Cheevarunothai Wang and Nihan 10 13 and the test data for roadway traffic emulation were previously recorded by the DEDAC system at a known location and time Since a Type 170 controller typically scans a loop detector at 60 Hz we configured both LOOPSIM and the DEDAC system to work at 60 Hz for this test The vehicle arrival pattern simulations feature was tested first We assumed there wa
18. inductance from the eddy currents more than offsets the increase from the ferrous mass and the net effect of the vehicle s presence is an overall reduction in loop inductance Therefore when a vehicle is on top of a loop detector it decreases the inductance of the loop This decrease in inductance then triggers the DEU s output relay or solid state circuit which in turn switches the output voltage to the controller to a low level close to O volts signifying that a vehicle s presence has been detected 1 Typically a controller scans loop detector outputs 60 times a second or at 60 Hz 2 3 To assure the effectiveness of actuated intersection signal control systems and freeway monitoring systems hardware and software of the systems should be tested before deployment However research laboratories where these tests are typically conducted generally do not have the field component of a loop detector system and therefore may not have live loop inputs for the tests Although controller cabinets have some built in test features system tests enabled by these features tend to be relatively simple Educators always try to prepare the next generation of traffic engineers with a profound understanding of traffic signal control systems and freeway monitoring systems The best way to achieve this goal is through hands on experience The problem is so similar to the testing of hardware and software of the traffic systems that the Cheevarunothai Wang
19. n PCMCIA port The recommended configurations of the laptop computer include Windows 2000 or Windows XP operating system a Pentium 4 processor and 512 MB of Double Data Rate Synchronous Dynamic Random Access Memory DDR SDRAM e Digital Input Output I O Card This card is required to connect the laptop computer with the PCMCIA port at one end and drive the mechanical relay circuits at the other end The number of I O channels needed depends on applications Each channel must be able to send events at 60 HZ or more In our implementation we selected the PC CARD D24 CTR3 digital I O card 9 It has 3 ports with eight channels for each port All 24 channels are programmable as input or output channels The output high is 3 0 v min 2 5 mA and output low is 0 4 v max 2 5 mA e Mechanical Relay Circuits Mechanical relay circuits selected in LOOPSIM must be drivable by the digital I O card In our implementation the compact Single Pole Single Throw SPST reed relay drivable with the PC CARD D24 CTR3 card was used The nominal current of the SPST reed relay is 20mA at 5VDC e Cable Connectors Normal 22 guage cables are used to connect the PC CARD D24 CTR3 card the mechanical relays Input File and the controller input LOOPSIM is designed to provide loop inputs to controller cabinets for testing and teaching purposes It supports channel connection tests vehicle arrival pattern simulations and roadway traffic emulations features Chan
20. nel connection tests are necessary to determine whether the test system has been correctly set up before formal test or teaching Some traffic control or operation algorithms must be tested with known arrival patterns The vehicle arrival pattern simulations feature provides direct support for such tests Most frequently a new algorithm is best Cheevarunothai Wang and Nihan 6 tested with traffic data collected from designated roadways The roadway traffic emulations feature reads a loop event data file recorded by the Detector Event DAta Collection DEDAC system 3 or the Advanced Loop Event Data Analyzer ALEDA 10 and replays them to emulate the roadway traffic exactly to the controller and the traffic event data collection system System Implementation Issues LOOPSIM was developed using the Microsoft Visual C NET technology 11 and the additional Universal Library documents from the manufacturer of the digital input output device 9 The program is executable on Windows 2000 or XP Windows operating system Since a traffic controller typically scans a loop detector s output at 60 Hz LOOPSIM should be able to simulate loop detector event data at 60 Hz or higher This requires using a high resolution timer in LOOPSIM implementation A timer is a program component that allows programmers to specify a recurring interval at which the elapsed event is raised in computer applications A multimedia timer is used in LOOPSIM for more accurate
21. ollers at an affordable cost is desirable for in laboratory traffic research and education This paper describes an affordable LOOP detector SIMulator LOOPSIM developed by the Smart Transportation Applications and Research Laboratory STAR Lab at the University of Washington UW LOOPSIM was designed to enable inductance loop detector outputs when the field component is absent LOOPSIM is a computer application with a supporting data communication device executable on Windows 2000 and XP operating systems If properly connected to a controller cabinet LOOPSIM and the DEU can form up a virtual inductance loop detector The only difference between this virtual loop detector and a real inductance loop is the method of actuating a call The real inductance loop s DEU senses the inductance change from the presence of a vehicle but the virtual loop places a call through the computer program of LOOPSIM and its relay circuit A controller cannot tell if a received call was from a virtual loop or a real loop Like a real inductance loop a virtual loop can be used to provide live inputs to controllers Additionally since loop detector inputs through a virtual loop are controllable a virtual loop can also be used to simulate inputs from traffic streams with different characteristics This is considered a very important feature because special tests and teaching that require inputs from traffic flows with specific traffic conditions can be designed and conduc
22. s a roadway section with eight lanes and each lane had two single loops deployed Figure 4 Channels 1 through 8 corresponded to the first eight loops and channels 9 through 16 corresponded to the second eight loops for lane 1 through lane 4 and lane 5 through lane 8 respectively The hourly vehicle volume was 500 for lane 1 From lane through lane 8 volume increases by 100 with each increase of lane number Average traffic speeds across lanes were assumed to be constant at 60 mph The test lasted 15 minutes The comparisons between the LOOPSIM created data and the DEDAC system received data are shown in Figure 5 a and 5 b The SENDC and RECVC curves represent the scan counts car from sending and receiving data files respectively Similarly vehicle time headways from sending and receiving data files are shown by SENDHW and RECVHW curves respectively There was a time delay of 16 milliseconds ms The mean absolute error between the two data sets was zero The sent event data sequence was preserved exactly in the received data file These test results indicate that LOOPSIM performed well at the 60 Hz working frequency and the accuracy was 100 Similarly the roadway traffic emulation feature was tested with the loop event data collected by the DEDAC system at 13 14 43 to 14 02 22 on May 16 2002 from station ES 163R on I 5 The simulated signal sequence by LOOPSIM and the received signal sequence by the DEDAC system are shown in Figure 6 a and 6 b
23. ted with the aid of LOOPSIM Such tests may not be feasible with real loop detectors whose Cheevarunothai Wang and Nihan 4 outputs are generally induced by uncontrollable traffic patterns and are not easily verified Consequently LOOPSIM offers an advantage to researchers and educators who can cost effectively set up a virtual loop detector and intentionally designate a traffic flow with desired characteristics for controlled laboratory studies in line with the purpose of their testing or teaching SYSTEM DESIGN AND IMPLEMENTATION System Components and Functions To simulate the output of an inductance loop to controllers LOOPSIM should have two output stages high voltage 12 volts and low voltage 0 volts High voltage represents the off status of an inductance loop 1 no vehicle is on the loop and low voltage represents the loop s status 1 a vehicle is on the loop Since communication ports of computers typically handle voltage between 0 volts and 5 volts an external power supply at 12 volt level 1 needed to meet the output requirements Considering that the Model 332 cabinet is most widely used in Washington State the LOOPSIM design was based on a Model 332 cabinet with a Type 170 controller The DEUs used were 222 series loop amplifier cards 8 When the field component of an inductance loop detector is missing the DEU stays in the open loop status which is typically a result of physical loop wire
24. tems To assure the effectiveness of these systems both hardware and software should be tested before deployment Additionally the hands on experience on traffic control systems is indispensable for the future generation of traffic engineers Field testing and teaching are generally not the first choice because any failure of the traffic system may cost too much Therefore in laboratory testing and teaching is preferred However live loop detector inputs may not be available in laboratories and this deficiency may seriously reduce the diversity of test and teaching methods LOOPSIM as described in this paper was designed to make live loop data inputs available in laboratories for traffic research and education It was developed using Microsoft Visual C NET technology and the additional Universal Library documents from the manufacturer of the digital input output device The program is executable on Windows 2000 or XP Windows operating system The hardware components of LOOPSIM include a laptop computer with a PCMCIA port a digital data I O card and mechanical relays Such a simple configuration is very affordable for research institutes and universities In our implementation less than 400 was spent for the hardware components connecting the laptop computer and the controller cabinet LOOPSIM 15 capable of generating output events of loop detectors at a high frequency 60 Hz and above Test results of LOOPSIM concluded that the system is reliable
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