MEASURING PERFORMANCE ON INTERRUPTED FLOW

FACILITIES WITH GPS PROBE AND BLUETOOTH TRAFFIC

MONITORING DATAReuben M. Juster, EIT

Stanley E. Young, P.E., Ph.D.

Elham Sharifi, Ph.D.

CATTworks

Vehicle Probes

• Alternative source of travel time data

• Third party vendors aggregate highway vehicles’ travel data

• Many different devices within or embedded in vehicles transmit the data

• Aggregated data is usually cleaned to get one reading per segment of roadway per time period

• Data available to users through web-interface / API

Car Manufacturers

Fleet Operators

Phone Manufacturers

Third Party Vendor

Cleaning

Us

Applications

Operations Planning

Traffic Management Centers

Picture Sources: WSDOT, VDOT, Creative Loafing ATL, Maryland SHA, FHWA

Traveler Info Performance MonitoringInvestment Justification

Not All Probe Data is Created Equal

• Probe data was first used for freeway-based applications

• Probe data users became interested in arterial-based applications

• The I-95 Corridor Coalition Vehicle Probe Project’s (VPP) validation program accessed the accuracy of the probe data

• Freeway data is generally more accurate than arterial data for several reasons

Fundamental Facility Differences

Freeways (Uninterrupted)

• High volumes

• Continuous Flow

Arterials (Interrupted)• Lower volumes

• Interrupted flow

• Red lights

• Driveways

• Adjacent land uses

• Not all arterials data is created equal

• Vary by volume, signalized intersections, driveways, geometry

• Mobility Vs. Accessibility

• Which arterials can have probe data to derive performance measurements?

Driveway

IntersectionInterrupted

Uninterrupted

VPP Validation

• Contract requires vendors to meet certain quality metrics

• This requires frequent validation studies on representative corridors to ensure that data meets metrics

• For freeways these metrics include Average Absolute Speed Error (AASE) and Speed Error Bias (SEB)

• These metrics work well for a uni-modal freeway travel time distributions, but not multi-modal arterial travel time distributions

Picture Sources: BTS, FHWA

Alternate Validation Method (1/2)

09/02 09/09 09/16 09/23 09/300

5

10

15

Date/Time

Trav

el T

ime

- Min

utes

Northbound

Traversals

Outliers

09/03/12 09/05/12 09/07/12 09/09/12 09/11/12 09/13/12 09/15/12 09/17/12 09/19/12 09/21/12 09/23/12 09/25/12 09/27/12 09/29/120

5

10

15Travel Time Plot - US Route 1 NB - between Telegraph Road and Fairfax County Parkway

Date & Time

Tra

vel T

ime (

min

ute

s)

Score > 25

BTM ^ VPP v

24 Hour Overlay Plot

Alternate Validation Method (2/2)

The Whole View

15%1.7

minutes

95%

7.7

minutes

𝑃𝑇𝐼 =95𝑡ℎ 𝑃𝑒𝑟𝑐𝑒𝑛𝑡𝑖𝑙𝑒

15𝑡ℎ 𝑃𝑒𝑟𝑐𝑒𝑛𝑡𝑖𝑙𝑒=

7.7

1.7= 4.5

Example 1 Corridor Description

• US-1, Mercer County, New Jersey (Princeton)

• 6-8 lanes total

• <1 Signal per mile, 3.2 miles long

• Grade separate interchanges

• Minimal access points

• Resembles a freeway

Example 1 Comparison

VPP

BTM

0 2 4 6 8 10 12 140

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Travel Time - Minutes

Per

cent

ile

Travel Time CFD Diagram

12AM 3AM 6AM 9AM 12PM 3PM 6PM 9PM 12AM0

2

4

6

8

10

12

14

Hour of Day 0-24

Trav

el T

ime

- M

inut

es

Hourly Overlay Scatterplot

PTI = 2.1

Example 2 Corridor Description

• US-130, Burlington County, New Jersey

• 6 lanes total

• 2 Signals per mile, 1.5 miles long

• Multi-cycle signal failures

Signalized Intersection

Grade-separate interchange

Example 2 Comparison

0 1 2 3 4 50

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Travel Time - Minutes

Pe

rce

ntil

e

Travel Time CFD Diagram

12AM 3AM 6AM 9AM 12PM 3PM 6PM 9PM 12AM0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Hour of Day 0-24

Tra

vel T

ime

- M

inu

tes

Hourly Overlay Scatterplot

VPP

BTM

PTI = 1.4

PTI = 2.5

Recommendations

Arterials likely to have accurate probe data

Arterials possibly to have accurate probe data

Arterials unlikely to tohave accurate probe data

• AADT >40000• 2+ lanes each

direction• <= 1 signals per mile• Principal Arterials• Limited Curb cuts• Confidently

characterize congestion and performance measures

• AADT 20K to 40K• 2+ lanes each direction• 1 to 2 signals per mile• Minor Arterials (HPMS) • Some segments work

(likely), others fail (unlikely)

• No cycle failures• Should be reviewed to

see effectiveness of probe data

• Low volume, AADT <20K

• >=2 signals per mile• Major collectors

(HPMS)• Probe data not

recommended• Frequent cycles

failures• Use re-identification

for performance monitoring

Future

• Probe data will improve with:

• Larger sample sizes

• Better processing (point pairing as opposed to instantaneous)

• Improved segmentation (already happening)

• Arterials that previously did not have accurate probe data may have accurate probe data (check every 18 to 24 months)

• In the mean time, verify validity if unknown

• Use the whole spectrum of the travel time distribution