This paper proposed an improved California Algorithm and recent patents for detecting
traffic incidents in urban roads. Traffic incidents in urban roads contribute 50% to 60% of the total
congestion delays. Incident detection involves the collection and the analysis of traffic data. The
common loop detectors were selected as the collected tool in this research. The existing incident detection algorithms are
more abundant, and mostly apply in freeways where the traffic flows are steady. The traffic incident detection algorithms
in urban roads should be developed. Based on the existing detection algorithms, an improved California Algorithm was
presented, which contained the adoptive dynamic threshold with the characters of traffic incidents and traffic flows in the
road network. Further detection results of the improved California Algorithm were judged by the OD matching regularity
of the volumes at the signal intersections to make the detection results fit with the actual flow feature. Finally, the data
collected by loop detectors was used to validate the proposed algorithm. The results showed that the improved algorithm
could predict the traffic incidents effectively, but there are still some false positives.
Keywords: California algorithm, dynamic threshold, loop detector, traffic incident.
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