The uniqueness of the BHL loop data derives from the fact that the BHL provides event data on individual vehicle actuations, accurate to 1/60th of a second. The BHL loop detector data collection and processing system operates continuously. Data is available through the
Services and Data Archive
page (login required, registration granted immediately) and
details on the structure and meaning of the data fields are explained on the
Data Format and Info page.
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* Note: This image is not of BHL.
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Additional enhancements to the BHL loop detector system were investigated
and implemented in 2003 under PATH Task Order 4134, “Loop Detector Data
Collection and Travel Time Measurement in the Berkeley Highway Laboratory.” Several
single and dual loop diagnostic tests were developed, allowing real-time evaluation
of the status of loop detectors. Vehicle reidentification techniques were improved,
resulting in higher frequency of reidentification while simultaneously reducing
error rate. A less expensive, simpler, and more robust communications system
was implemented using off-the-shelf components. Also, BHL loop detector system
technologies were modified to make them more adaptable to different cabinet,
station, and loop configurations so that a BHL-style system could be more easily
deployed in new locations.
There are 7 major components of the BHL data collection and processing system.
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Click for bigger image.
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Data is collected from the loop controllers every second by General Packet Radio Service (GPRS) modems and sent via TCP/IP to the Data Collection Server
on the UC Berkeley campus. Software running on this computer records the raw
modem data in local files and also transmits the data to a database running
on a separate computer. Most of the BHL data computation and display tools
extract data directly from this database. As 1/60 second field data is recorded
in the database, software running on a dedicated computer computes 30 second
averages. The results of these calculations are stored back in the database, and sent to Caltrans.
Also running continuously, the Vehicle Re-identification and Travel Time Processor
extracts raw data, and feeds the computational results back
into the database. This data processing computer also sends 30 second data
to Caltrans District 4 via a dedicated frame relay data line.
The UC Berkeley Institute of Transportation Studies Web server runs software
that can query the database and present BHL data numerically and graphically.
These features are publicly accessible.
If you would like more details or want to inquire about services not mentioned, please feel free to email us at bhl@calccit.org.