Traffic Volume Data Collection

Daniel Jenkins, PESubstitute – Steven Jessberger

Office of Highway Policy InformationOctober 23, 2012

Why Collect Volume Data?

• Planning/Environment• Project Development• Operations• OHPI needs it• MAP-21

Planning/Environment Needs

• Air quality analysis• Noise studies• Traffic projections

Project Development Needs

• Interchange Justification Reports• Design• Maintenance of Traffic Decisions

Operations needs

• Traffic signal timing• HOV operations• Work zone decisions

OHPI Needs

• HPMS• Monthly TVT report• Temporal Traffic Studies

TVT Report• Data Requirements

– ATR data submitted to TMAS by the 20th of the month after the close of the month

– TMAS software performs a number of quality checks on data• 7 day error• 7 zero hour error• Adjacent hour error• Directional split error• MADT check same month year to year• Maximum volume per hour per lane (new in 2012)

Report available at http://www.fhwa.dot.gov/ohim/tvtw/tvtpage.cfm

Who wants TVT?

• Automotive industry companies• Insurance companies• Financial services• Retail

MAP-21

• National freight policy– Designate National freight network (AADTT)

• HSIP– Traffic data defined as safety data Crash rates

based on VMT• Performance measures

– Congestion reduction– System reliability

QUALITY DATA

Guidance• AASHTO Guidelines for traffic data programs• Traffic Monitoring Guide (TMG)• HPMS field Manual

Types of Sensors

• In road/on road– Loops– Piezos (axle sensors)– Tubes

Types of Sensors- cont.

• Off road– Infrared– Magnetic– Radar– Microwave– Acoustic– Video

Factors

• Monthly Factors• Day of Week Factors• Axle Correction Factors• Yearly Growth/Reduction Factors

Determining an accurate AADT is very important to a successful program!

Factors Example - SeasonalRural Interstate Seasonal Factors

00.20.40.60.81

1.21.41.6

Month

Ad

jus

tme

nt

Fa

cto

r

2002

2001

2000

1999

1998

Average

Factors Example – DOW 2002 Rural Interstate Weekday Comparison

0.95

1

1.05

1.1

1.15

Jan

Feb

Mar

Apr

May Jun

Jul

Aug

Sep Oct

Nov

Dec

Months

Fact

ors Mon-Thur

Mon-Fri

Factors

• Misusing the DOW factor can lead to a 5% underestimate

• Misusing the Monthly factor can lead to a 15% overestimate

• Do you factor and are you following the TMG or some other method?

Problem

• The DOT did a traffic count on a minor rural collector (Site A) between January 26-28 (Tuesday-Thursday). The total count for three days was 3,600 vehicles. Calculate the AADT for Site A.

Solving Problem

• Locate an ATR on a similar class facility

Solving Problem

• Locate an ATR on a similar class facility– Found a ATR on a rural minor collector in the

adjacent county with the following characteristics:• 290,800 veh./yr.• January traffic- 19,800 veh.

Solving Problem

• Locate an ATR on a similar class facility– Found a ATR on a rural minor collector in the

adjacent county with the following characteristics:• 290,800 veh./yr.• January traffic- 19,800 veh.

– Calculate AADT and MADT for the ATR site• AADT=290,800/365= 797, say 800 vpd• MADT= 19,800/31= 640 vpd

Solving Problem

• Locate an ATR on a similar class facility– Found a ATR on a rural minor collector in the

adjacent county with the following characteristics:• 290,800 veh./yr.• January traffic- 19,800 veh.

– Calculate AADT and MADT for the ATR site• AADT=290,800/365= 797, say 800 vpd• MADT= 19,800/31= 640 vpd

– Compute monthly correction factor• AADT/MADT = 800/640 = 1.25

Solving Problem

• Determine AADT for Site A

Solving Problem

• Determine AADT for Site A– Calculate ADT for site A

• ADT= 3,600/3= 1,200 vpd

Solving Problem

• Calculate AADT for Site A– Calculate ADT for site A

• ADT= 3,600/3= 1,200 vpd

– Calculate AADT• AADT= 1,200 X 1.25= 1,500 vpd

DOW factor would also need to be applied

Data- Collect once, correctly anduse many times

QUESTIONS?????????????

Danny Jenkins, PEVolume Program Manager

202-366-1067daniel.jenkins@dot.gov