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

Additional:• choosing appropriate parameter settings• control of triggering speed

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

occupancy time vs. speed

5 10 15 20 250

1

2

3

4

5

6

7

8

Vehicle speed (mph)

Occ

upan

cy ti

me

(s)

3m4m5m11m16m

detection uncertainty

detection regions

red = alert

possible alert

green = no alert

detection regions

red = alert

possible alert

green = no alert

length distribution (M25 site 4762, 4 May 2002 11:19-18:28)

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

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

HIOCC2 detection regions

HIOCC2 architecture

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

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

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)

pre-processing detection regions

simulation

• 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]

time

1-second occupancy(Instantaneous Occupancy)

tocc n-1 tuocc n-1 tocc n

length/speed headway length/speed

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

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

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)

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

improved

current