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HIOCC Developments

HIOCC Developments. SEA HA. overview. problems with HIOCC developments to address problems simulation using Individual Vehicle data demonstration of simulator tool. HIOCC problems. Key: false alerts due to HGVs long clearance time under low flow poor detection during night

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HIOCC Developments

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  1. HIOCC Developments SEA HA

  2. overview • problems with HIOCC • developments to address problems • simulation using Individual Vehicle data • demonstration of simulator tool

  3. HIOCC problems Key: • false alerts due to HGVs • long clearance time under low flow • poor detection during night Additional: • choosing appropriate parameter settings • control of triggering speed

  4. understanding false alarms / detection • speed-length ambiguity since using only occupancy data • 2.0s occupancy = 4m car at 6.7mph • 2.0s occupancy = 16m HGV at 20.1mph • no synchronisation between arrival of vehicle at detector and start of instantaneous occupancy measuring interval • for occupancy times 2.0s-2.8s, only some vehicles will trigger • 2.9s needed to guarantee alert  slower detection speed

  5. occupancy time vs. speed

  6. detection uncertainty

  7. detection regions green = no alert possiblealert red = alert

  8. detection regions green = no alert possiblealert red = alert length distribution (M25 site 4762, 4 May 2002 11:19-18:28)

  9. clearance under low flow • caused by suspension of smoothed occupancy calculation • feature intended to prevent alert fluctuation in stop-go traffic, but cannot distinguish from case of no vehicles after (false) alert in very low flow  alert does not clear on otherwise empty lane

  10. development of HIOCC2 • make use of individual vehicle speed data • trap and suppress false alerts raised by HIOCC • doesn’t modify basic HIOCC algorithm • maintain detection performance • tried and tested • HIOCC2 easily switched out to revert to standard HIOCC • robustness to missing/outlier speed data • robustness to single loop failure

  11. HIOCC2 detection regions

  12. HIOCC2 architecture

  13. HIOCC2 key points • Watchdog suppresses HIOCC alert if speed > threshold  removes false alerts • smoothed speed for clearance • clear only after n vehicles passed  tolerance to outlier speed • force HIOCC to clear if smoothed occupancy calculation suspended • Watchdog output forced high if loop fails  revert to HIOCC • data synchronisation to align occupancy and speed data

  14. HIOCC2 issues • algorithm introduces 3 second delay • robust detection in case of vehicle stopping on first loop but not reaching second • to ensure suppression of long vehicle false alarms • potential for using the time for pre-processing to improve HIOCC detection • significant reduction in false alarm rate • detection performance of HIOCC not changed • threshold speed controllable

  15. improving HIOCC detection • aim to remove the uncertain detection region through pre-processing occupancy • overcome the problem of synchronisation • features : • raise detection speed • self-contained, no modification to HIOCC • imposes 1 second delay 6kmh (1.68m)

  16. pre-processing detection regions

  17. simulation length/speed headway length/speed • simulation of HIOCC based on logged IVD data • software tool developed to simulate HIOCC/HIOCC2 • step through second-by-second and view/plot internal variables, inputs, outputs • measure overall performance • automatically test different parameter combinations • read IVD logged from different Outstations:[Peek, Golden River, Siemens]

  18. benefits • open up ‘black-box’ to understand / visualise operation in different traffic conditions • test algorithm on specifically generated test examples and situations • ‘what if’ testing • rapidly and automatically try out different parameters

  19. dataset from M25 • dataset collated from M25 Individual Vehicle Data (May 2002) • examples of incident / non-incident / HIOCC false alerts for use in the simulator • different location types: hill, junction, normal • different traffic flows

  20. potential development Get as much as possible from existing equipment. • aim to improve control and allow higher triggering speed • iterate HIOCC at faster rate (e.g. every 0.5s)

  21. summary • developments have been carried out that: • address problems of HIOCC • keep the underlying HIOCC algorithm, which is always used as a failsafe fallback • simulation tool now available

  22. improved

  23. current

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