Copyright © Siemens plc 2009. All rights reserved.

Above ground SCOOT and MOVA detection in practice

Page 2September-09 Siemens Mobility / Traffic Solutions

Backgound

SCOOT and MOVA are the strategies of choice for many Traffic Managers

Both require accurate data about traffic conditions

Traditionally this is supplied by loops

Loops have many advantages, but also some disadvantages

Obvious solution is to use above ground solutions!

Advantages of loops

• Accurate• Precise detection zone and position• Immune to weather and lighting conditions• Almost invisible when installed• Can’t easily be stolen

Disadvantages of loops

• Difficult to install• Vulnerable to damage

• Movement of the road surface• Destruction when services are accessed

• Difficult to repair

Page 3September-09 Siemens Mobility / Traffic Solutions

Possible above ground technologies

Several alternatives sensor technologies assessed by Siemens Corporate Technology (CT)

Some found more suitable than others

77GHz radar seemed the best option

Advantages

• Passive so can be very low power• Accurate zones if multiple sensors used• Immune to changing light levels• Relatively low cost• No significant maintence required

Disadvantages

• Not good for detecting slow / static traffic

• Can be affected by environment (rain / snow etc)

Passive Acoustic

Technology

• Immune to light levels• Relatively low cost• No significant maintenance required

• Difficult to achieve precise detection zone

• Heavy rain / wind and snow can severally affect performance

Active Acoustic

• Immune to changing light levels• Very accurate zones possible• No significant maintenance required

• Active device so needs radio approval in all target markets

77GHz Radar

• Passive so can be very low power• Reasonably accurate zones possible• Relatively low cost• No significant maintenance required

• Can be affected by significant sudden temperature shifts

• Fog and heavy snow can affect performance

Passive Infrared

• Many accurate zones possible (if field of view permits)

• Can provide visual overview of target area

• Can be badly affected by changing light levels and environmental conditions (Rain, snow etc).

• Significant maintenance overhead

Video

Page 4September-09 Siemens Mobility / Traffic Solutions

Benefits of 77GHz radar

Excellent target resolution Able to deliver very precise

detection zones

Important if SCOOT and MOVA loops are to be emulated accurately.

Good immunity to adverse weather

Small antenna size Minimal visual impact on-street

Widespread acceptance of the frequency band

Detector could be used worldwide with few limitations

Page 5September-09 Siemens Mobility / Traffic Solutions

Benefits of 77GHz radar

But there was a big problem

Cost!!!

Detailed evaluation showed although it offered a very good technical solution, solid state 77GHz technology was in its infancy and the product costs were found to be very high.

However, radar operating at 24GHz seemed to offer similar benefits at a much lower cost

Page 6September-09 Siemens Mobility / Traffic Solutions

Development challenges

Product cost is a very significant driver when choosing technology solutions

If these are too high product adoption in the market will tend to be limited, even if the performance achieved is good

One interesting solution relates to the cost optimisation of the radar antenna and related circuits

Page 7September-09 Siemens Mobility / Traffic Solutions

Experiences in practice

First tests based on “ground truth” principals at Poole test site

Loop comparison Various traffic and weather

conditions

Initially only count and occupancy gathered in 5 minute bins

Results looked very good

Page 8September-09 Siemens Mobility / Traffic Solutions

Experiences in practice

Flow : Loop Versus Heimdall (20/5/09 to 29/5/09)

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Page 9September-09 Siemens Mobility / Traffic Solutions

Experiences in practice

First tests based on a “ground truth” approach at Poole test site

Loop comparison Various traffic and weather

conditions

Initially only count and occupancy gathered in 5 minute bins

Results looked good

But its is easy to be fooled by simple graphs!

Focusing on the variation between the loop and Heimdall seemed to showed a different picture

Page 10September-09 Siemens Mobility / Traffic Solutions

Experiences in practice

Delta Flow (Percentage Variation) Between Loop and Heimdall

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Page 11September-09 Siemens Mobility / Traffic Solutions

Delta Flow (Percentage Variation) Between Loop and Heimdall

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Difference between loop v Heimdall (Extract)Delta Flow (Percentage Variation) Between Loop and

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Experiences in practice

Biggest variation occurred at night

few vehicle in the sample set

loop was found to be missing some fast moving motor cycles which Heimdall detected.

Also the loop detected a number of vehicles driving close to the loop but in the opposite direction,

Its easy to adjust Heimdall to avoid these vehicles

Overall conclusion was that Heimdall count and occupancy performance looks good

Page 12September-09 Siemens Mobility / Traffic Solutions

Implications SCOOT

SCOOT uses a measure of linear discounted occupancy to model queue build-up and dispersal (Link Profile Units - LPUs)

The way a detector responds can significantly affect the LPU values that SCOOT calculates

Typical detector sample

250ms data 0 0 1 1 1 1 0 0 0 0 0 1 1 1 1 1 0 0 0 0 1 1 1 0 0 1 1 0 0 0Discounted occupancy 7 6 5 4 7 6 5 4 3 7 6 5 7 6Resulting LPU value = 78 22 1825 13

250ms data 0 0 0 1 1 1 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 1 1 0 0 0 1 0 0 0Discounted occupancy 7 6 5 7 6 5 4 7 6 7Resulting LPU value = 60 718 22 13

Detector with poor turn-on response

250ms data 0 0 1 1 0 1 0 0 0 0 0 1 1 1 0 1 0 0 0 0 1 0 1 0 0 1 1 0 0 0Discounted occupancy 7 6 7 7 6 5 7 7 7 7 6Resulting LPU value = 72 7 7 7 713 18 13

Detector with poor hold characteristics

Count value accurate

LPU value significantly lower

Count value high

LPU value only slightly lower (but likely not be consistent)

Page 13September-09 Siemens Mobility / Traffic Solutions

Implications SCOOT – LPU on test site

Initial Heimdall LPU performance was disappointing!

Further refinement of the detection algorithm proved necessary

Performance much improved as a result.

Still produces a slight lower LPU value than the loop

Heimdall detection zone about 10% smaller than the loop

Would be accounted for during normal validation of the link

LPU : Loop Versus Heimdall (20/5/09 to 29/5/09)

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LPU:- Loop v Heimdall

Page 14September-09 Siemens Mobility / Traffic Solutions

Heimdall extended trials

Several further Heimdall trial installations have been undertaken

Different arrangements have been tested,

Live installations With and without reference

loops

A full set of detailed results on all the trials will be available from the Siemens website

Poole – Fleetsbridge Roundabout (SCOOT – count site)

Southampton – Bittern Triangle (SCOOT)

Bournemouth – Cemetery Junction (SCOOT – count site)

Cardiff - Leckwith Giratory (SCOOT)

Winchester. Battery Hill (SCOOT)

Wimborne - Willett Arms (MOVA)

Heimdall trial sites

Page 15September-09 Siemens Mobility / Traffic Solutions

Winchester – Battery Hill

A single SCOOT detector has been installed in Winchester, along side a reference loop used by TRL.

Data still being gathered from the Hampshire UTC system.

Count correlation between loop and Heimdall were very good.

LPU results re-confirmed that the Heimdall detection zone is a little smaller than a standard loop, but acceptable

A view confirmed by a TRL assessment of the data from this site

Poole – Fleetsbridge Roundabout (SCOOT – count site)

Southampton – Bittern Triangle (SCOOT)

Bournemouth – Cemetery Junction (SCOOT – count site)

Cardiff - Leckwith Giratory (SCOOT)

Winchester. Battery Hill (SCOOT)

Wimborne - Willett Arms (MOVA)

Heimdall trial sites

Romse

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Battery Hill

SCOOT Loop versus Heimdall - FlowNov. 1st - Nov. 10th 2008

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Battery Road – LPU (Reference loop v Heimdall)

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SCOOT Loop versus Heimdall - FlowNov. 1st - Nov. 10th 2008

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Page 16September-09 Siemens Mobility / Traffic Solutions

Summary

The Heimdall detector provides good correlation to a loop

Count accuracy is excellent

SCOOT LPU values are a little lower than a standard loop but this can be addressed during validation

MOVA performance has also been shown to be acceptable

A full report on the Heimdall trials will be available from the Siemens website

Copyright © Siemens plc 2009. All rights reserved.

Above ground SCOOT and MOVA detection in practice