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There are 7 major components of the BHL data collection and processing
system (diagram). Data is collected
from the loop controllers every second by CDPD (Cellular Digital
Packet Data) modems and sent via TCP/IP to the Data Collection Server
on the UC Berkeley campus. Software running on this computer records
the raw CDPD 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.
Also running continuously, the Vehicle Re-identification and Travel
Time Processor extracts raw data from the database 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.
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