1

Temporal Aggregation Effects on ITS Data

ApplicationsSustainable transportation performance measures

ITS Data Aggregation Effects – Alex Bigazzi

Alex BigazziPortland State University

2

Objective

ITS Data Aggregation Effects – Alex Bigazzi

Effects of time-aggregating data on sustainability performance measures

• Emissions• Fuel Consumption

Speed distributions

• Delay

Travel time estimates

3

Data Source• ~2 miles of M4 in London• Individual arrival times and speeds• 24hr data over 5 weeks (1998)• 500 meter spacing

1 2 3 4 5 6 7 8

ITS Data Aggregation Effects – Alex Bigazzi

4

SPEED DISTRIBUTIONSand effects on related measures

ITS Data Aggregation Effects – Alex Bigazzi

6

Speed Consolidation

ITS Data Aggregation Effects – Alex Bigazzi

1 20 60 300 600 900

02

04

06

0

7am Speeds byAggregation Level

Aggregation Width (sec)

Sp

ee

d (

mp

h)

1 20 60 300 600 900

40

50

60

70

11am Speeds byAggregation Level

Aggregation Width (sec)

Sp

ee

d (

mp

h)

11-16-98, station 172

7ITS Data Aggregation Effects – Alex Bigazzi

Speed Consolidation

Emissions

Fuel ConsumptionSafety

8

TRAVEL TIME

ITS Data Aggregation Effects – Alex Bigazzi

9ITS Data Aggregation Effects – Alex Bigazzi

Endpoint method of travel time estimation

10ITS Data Aggregation Effects – Alex Bigazzi

x

t

Travel

Sampling Error

True Trajectory

Speed-Estimated Trajectory

Detector

Detector

Sampling Error – neglected here

11ITS Data Aggregation Effects – Alex Bigazzi

x

t

Travel

Grouped Speed Error

Individual Speed

Trajectories

Average Speed

Trajectory

Detector

Detector

Grouped Speed Error

12ITS Data Aggregation Effects – Alex Bigazzi

1 week of speedsArithmetic Mean Speed (mph)

Harm

onic

Mean S

peed (

mph)

13

Estimate space mean speed from time mean speed

2

4 22

ttts

vvv

t

t

t

s

vCV

CVv

v

2

41

21

Rearranging:

ITS Data Aggregation Effects – Alex Bigazzi

Ref: Lindveld and Thijs

14

1min data (one day, one station)

0.0 0.1 0.2 0.3 0.4 0.5

0.5

0.6

0.7

0.8

0.9

1.0

COV

SM

S/T

MS

ITS Data Aggregation Effects – Alex Bigazzi

CV

Histogram of COV

COV

Fre

qu

en

cy

0.0 0.5 1.0 1.5

02

00

04

00

06

00

08

00

01

00

00

12

00

0

CV

15

10 20 30 60 120 300 600 900 1800 36000%

20%

40%

60%

80%

100%SMS estimates within 1% of

true value

Aggregation Width (sec)

ITS Data Aggregation Effects – Alex Bigazzi

16

DELAYCombined effects of speed distribution and travel time

errors

ITS Data Aggregation Effects – Alex Bigazzi

17ITS Data Aggregation Effects – Alex Bigazzi

80

60

40

20

0

Sp

eed

4:00 8:00 12:00 16:00 20:00

FFS

18

One week of delay (all stations)

10 20 30 60 120 300 600 900 1800 3600

Aggregated Delay, Calulated and Lost

Aggregation Width (sec)

Dela

y (1

000 h

ours

)

0

5

10

15

20

Aggregate EstimateDistribution ErrorTMS Error

ITS Data Aggregation Effects – Alex Bigazzi

Disaggregate

20ITS Data Aggregation Effects – Alex Bigazzi

10 20 30 60 120 300 600 900 1800 36000

5

10

15

20

25

TMS

Estimated SMS

True SMS

Disaggregate

Aggregation Width (sec)

Tota

l D

ela

y(1

,00

0 h

ou

rs p

er

dete

ctor-

mile)

21

Conclusions

ITS Data Aggregation Effects – Alex Bigazzi

With respect to disaggregate data:• Speed consolidation

- Underestimate emissions, fuel• Travel time

- TMS underestimates TT and delay

- Est. SMS from TMS and variance

22

Considerations Costs of data management Future uses for data Missing or bad data Other summary statso Varianceo Harmonic meano Median

ITS Data Aggregation Effects – Alex Bigazzi

23

Thank you!

? ? ?ITS Data Aggregation Effects – Alex Bigazzi

AcknowledgementsDr. Robert Bertini, Helene Siri, Stuart Beale, Tim Rees, and OTREC

Questions?