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Traffic Count Frequently Asked Questions
The information below is intended to explain key definitions and processes associated with the Annual Traffic Count Program provided by the Tennessee Department of Transportation on behalf of the Johnson City MPO planning region.
Table of Contents
- What is the definition of "ADT"?
- How is traffic count data collected?
- What are traffic counts used for?
- How often will the traffic counts be updated?
- What is a traffic count station?
- Why do the counts seem to vary so much from year to year?
- Why is data not provided for some count locations shown on the map?
Please let us know if the questions and answers are helpful and if you found the answer to your question. To forward a comment or question to the staff e-mail your questions to jcmpo@jcmpo.org.
What
is the definition of "ADT"?
ADT stands for average daily traffic. On any given day this would be the
average number of vehicles traveling on a particular road.
Back to top
How is traffic count data collected?
Vehicles are counted by the Tennessee
Department of Transportation (TDOT) in all 95
counties in Tennessee, each year. Mechanical traffic counting devices
are deployed along the roadside (usually secured to a utility pole) and
a rubber “road tube” is placed across each traffic lane. Pressure
from vehicles crossing the rubber tube is detected by the mechanical counter
(a small box comparable in size to a car battery) and electronically stored
by the counter. The “road tube counters” are placed on a section
of highway for a minimal 24-hour period then moved to another location.
The collected data is then sent to TDOT central offices in Nashville for
processing. The raw counts are then adjusted using a formula to calculate
the Average Daily Traffic. This adjustment takes
into consideration weekday and time of year variations.
Traffic
count data is used by state and local transportation officials in
the planning of road improvements and monitoring of traffic conditions.
In the private sector - realtors, bankers, developers, economic development
agencies, as well as citizens also use traffic count data
for a a variety of purposes. This information is provided via
this web site as a service from the Tennessee Department of Transportation
in partnership with the University of Tennessee Transportation Center
and the Johnson City MPO. Back to top
How often will the counts be updated?
As mentioned earlier, TDOT has an established
program for counting traffic in each Tennessee county every year. In the
Johnson City area this is usually done in the fall (October or November),
depending upon the statewide schedule. By the time the data is processed
and transmitted back to the MPO staff, sometimes a new calendar year has
started. So the counts may have taken in November would likely not
be ready for web posting before spring or summer of of the next year.
What is a traffic count station?
A traffic count station is a designated location for traffic data to be collected each year. The numbers on the map indicate station numbers from the Tennessee Department of Transportation's numbering system. The detailed traffic sheets have a street name or highway number along with 2 intersecting roads to help you locate that station. The table also includes the individual station numbers listed below the map if the map link to the data is not working properly. Back to top
Why do the traffic counts seem to vary so much
from year to year?
The traffic counts only indicate traffic detected during the week the
counters were placed at a given location each year. During the course
of a year most roadways experience a range of values depending upon land
use activities in the area. The counts for a given year may be affected
by road closings or detours from another route or a variety of conditions
that may occur. A more important indicator of long term traffic
patterns would be the trend line located at the bottom of the information
page. Variations of 10% to 20% of an increase or decrease
would not be uncommon from year to year. The Johnson City counts
are taken when East Tennessee State University is in session which is
an important factor in local and regional travel patterns. The
Johnson City MPO staff is working on an Intelligent Transportation Systems
project in which permanent electronic count equipment will provide automated
counts at several key locations continuously for ongoing traffic monitoring
purposes. Back to top
Why is data not provided for some locations
shown on the map?
Traffic counts are provided to the MPO by TDOT for both Washington
and Carter Counties, not just Johnson City. The MPO staff feels
it is important for all the data to be accessible by the web, even though
we do not have an interactive map for the counties at this time.
Occasionally, there is a count station with no detailed traffic count
sheet. This station has been retired. This could be due to a new road
replacing the older road, or a new alignment, or it was decided traffic
counts were no longer needed, so the station number was retired.
| Acknowledgements |
| TDOT |
| Federal Highway Administration (Tennessee Division Office) |
Johnson City MTPO 137 W. Market Street Johnson City, TN 37604. Site Created by: Johnson City Metropolitan Transportation Planning Organization Copyright ©2010 JCMPO All Rights Reserved.