Annual average daily traffic

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Annual average daily traffic, abbreviated AADT, is a measure used primarily in transportation planning, transportation engineering and retail location selection. Traditionally, it is the total volume of vehicle traffic of a highway or road for a year divided by 365 days. AADT is a simple, but useful, measurement of how busy the road is.

Contents

AADT is the standard measurement for vehicle traffic load on a section of road, and the basis for most decisions regarding transport planning, or to the environmental hazards of pollution related to road transport. [1] [2]

Uses

Highway 401 in Ontario, Canada, has an AADT of over 410,000 in some sections of Toronto. Highway 401 east of Highway 400.jpg
Highway 401 in Ontario, Canada, has an AADT of over 410,000 in some sections of Toronto.

One of the most important uses of AADT is for determining funding for the maintenance and improvement of highways.

In the United States the amount of federal funding a state will receive is related to the total traffic measured across its highway network. Each year on June 15, every state in the United States submits a Highway Performance Monitoring System HPMS report. The HPMS report contains various information regarding the road segments in the state based on a sample (not all of the road segments) of the road segments. In the report, the AADT is converted to vehicle miles traveled (VMT). VMT is the AADT multiplied by the length of the road segment. To determine the amount of traffic a state has, the AADT cannot be summed for all road segments since an AADT is a rate. The VMT is summed and is used as an indicator of the amount of traffic a state has. For federal-funding, formulas are applied to include the VMT and other highway statistics.

In the United Kingdom AADT is one of a number of measures of traffic used by local highway authorities, Highways England and the Department for Transport to forecast maintenance needs and expenditure. [4]

Data collection

A traffic counter on BIA Road J-9 in the United States Traffic Counter on BIA Road J-9.jpg
A traffic counter on BIA Road J-9 in the United States

To measure AADT on individual road segments, traffic data is collected by an automated traffic counter, hiring an observer to record traffic or licensing estimated counts from GPS data providers. There are two different techniques of measuring the AADTs for road segments with automated traffic counters. One technique is called continuous count data collection method. This method includes sensors that are permanently embedded into a road and traffic data is measured for the entire 365 days. The AADT is the sum of the total traffic for the entire year divided by 365 days. There can be problems with calculating the AADT with this method. For example, if the continuous count equipment is not operating for the full 365 days due to maintenance or repair. Because of this issue, seasonal or day-of-week biases might skew the calculated AADT. In 1992, AASHTO released the AASHTO Guidelines for Traffic Data Programs, [5] which identified a way to produce an AADT without seasonal or day-of-week biases by creating an "average of averages." For every month and day-of-week, a Monthly Average Day of Week (MADW) is calculated (84 per year). Each day-of-week's MADW is then calculated across months to calculate an Annual Average Day of Week (AADW) (7 per year). Finally, the AADWs are averaged to calculate an AADT. The United States Federal Highway Administration (FHWA) has adopted this method as the preferred method in the FHWA Traffic Monitoring Guide. [6]

While providing the most accurate AADT, installing and maintaining continuous count stations method is costly. Most public agencies are only able to monitor a very small percentage of the roadway using this method. Most AADTs are generated using short-term data collection methods sometimes known as the coverage count data collection method. Traffic is collected with portable sensors that are attached to the road and record traffic data typically for 2 – 14 days. These are typically pneumatic road tubes although other more expensive technology such as radar, laser, or sonar exist. After recording the traffic data, the traffic counts on the same road segment are taken again in another three years. The FHWA Traffic Monitoring Guide [6] recommends performing a short count on a road segment at a minimum of every three years. There are many methods used to calculate an AADT from a short-term count, but most methods attempt to remove seasonal and day-of-week biases during the collection period by applying factors created from associated continuous counters. Short counts are taken either by state agencies, local government, or contractors.

For the years when a traffic count is not recorded, the AADT is often estimated by applying a factor called the Growth Factor. Growth Factors are statistically determined from historical data of the road segment. If there is no historical data, Growth Factors from similar road segments are used.

Similar measures

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Federal Highway Administration United States government agency

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M-152 is a state trunkline highway in the US state of Michigan in Cass and Van Buren counties. The highway runs through the Sister Lakes area providing access to the lake cabins and adjoining farmlands. The highway has existed mostly unchanged since the designation was commissioned in the 1930s.

Kentucky Route 212 is a short state highway located in Boone County, in the northern region of the U.S. state of Kentucky. The highway is approximately 1.3 miles (2.1 km) long, and partially constructed as a freeway, with the rest being a divided highway. The roadway links Interstate 275 (I-275) to the Cincinnati/Northern Kentucky International Airport, and has been designated as a connector route by the Federal Highway Administration (FHWA). A road first appeared near the location of KY 212 around 1937. A short road was built in the location of KY 212 when the U.S. Army Air Corps built the predecessor to the CVG Airport. The road was reconstructed to a divided highway in 1972, and has remained relatively unchanged since.

State Route 906 (SR 906) is a 2.65-mile-long (4.26 km) state highway in the U.S. state of Washington, serving Snoqualmie Pass and its associated ski areas in King and Kittitas counties. The highway travels southeast between two interchanges with Interstate 90 (I-90) in Snoqualmie Pass and Hyak. SR 906 was formed out of segments of the former Sunset Highway that were bypassed by the construction of the controlled-access Interstate Highway over the pass. Between 360 and 2,100 vehicles use the road on an average day in 2012.

Washington State Route 223 Highway in Washington

State Route 223 (SR 223) is a 3.81-mile (6.13 km) long state highway located entirely in Yakima County, Washington, United States. It has served the role of connecting the city of Granger to the county seat, Yakima via Interstate 82 and to SR 22 since its establishment in 1967, serving between 4,000 and 8,500 cars per day on average in 2009.

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Highway 396 is a former state highway near Burlington in Boone County. Between designation as a state highway in 1973 and decommissioning to the county road system in 2016, it was maintained by the Arkansas Department of Transportation (ArDOT).

Traffic count

A traffic count is a count of vehicular or pedestrian traffic, which is conducted along a particular road, path, or intersection. A traffic count is commonly undertaken either automatically, or manually by observers who visually count and record traffic on a hand-held electronic device or tally sheet. Traffic counts can be used by local councils to identify which routes are used most, and to either improve that road or provide an alternative if there is an excessive amount of traffic. Also, some geography fieldwork involves a traffic count. Traffic counts provide the source data used to calculate the Annual Average Daily Traffic (AADT), which is the common indicator used to represent traffic volume. Traffic counts are useful for comparing two or more roads, and can also be used alongside other methods to find out where the central business district (CBD) of a settlement is located. Traffic counts that include speeds are used in speed limit enforcement efforts, highlighting peak speeding periods to optimise speed camera use and educational efforts.

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Traffic simulation

Traffic simulation or the simulation of transportation systems is the mathematical modeling of transportation systems through the application of computer software to better help plan, design, and operate transportation systems. Simulation of transportation systems started over forty years ago, and is an important area of discipline in traffic engineering and transportation planning today. Various national and local transportation agencies, academic institutions and consulting firms use simulation to aid in their management of transportation networks.

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Arkansas Highway 267

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Long-Term Pavement Performance Research project

Long-Term Pavement Performance Program, known as LTPP, is a research project supported by Federal Highway Administration (FHWA) to collect and analyze pavement data in the United States and Canada. Currently, the LTPP acquires the largest road performance database.

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Pavement performance modeling

Pavement performance modeling or pavement deterioration modeling is the study of pavement deterioration throughout its life-cycle. The health of pavement is assessed using different performance indicators. Some of the most well-known performance indicators are Pavement Condition Index (PCI), International Roughness Index (IRI) and Present Serviceability Index (PSI), but sometimes a single distress such as rutting or the extent of crack is used. Among the most frequently used methods for pavement performance modeling are mechanistic models, mechanistic-empirical models, survival curves and Markov models. Recently, machine learning algorithms have been used for this purpose as well. Most studies on pavement performance modeling are based on IRI.

Highway 262 is an east–west state highways in Woodruff County, Arkansas. The route is maintained by the Arkansas Department of Transportation (ARDOT).

Highway 364 is an east–west state highway in Cross County, Arkansas. The highway connects a series of rural communities and farmland to the principal north-south highways in Cross County. Highway 364 is maintained by the Arkansas Department of Transportation (ArDOT). A former designation, also in Cross County, connected Togo to the state highway system between 1973 and 1983.

Highway 207 is a north–south state highway in Dallas County, Arkansas. It was created in 1962 along a former county road. The route is maintained by the Arkansas Department of Transportation (ArDOT). A former designation in the same vicinity was deleted in 1973.

References

  1. Gauderman, W James; et al. (2005). "Childhood Asthma and Exposure to Traffic and Nitrogen Dioxide".
  2. Gary A. Davis (2007). "Accuracy of Estimates of Mean Daily Traffic: A Review". Archived from the original on 2012-07-16.
  3. "Provincial Highways, Traffic Volumes, 2016" (PDF). Ontario Ministry of Transportation . Retrieved 2021-09-24.
  4. DfT Road Traffic Statistics https://roadtraffic.dft.gov.uk/about
  5. AASHTO Guidelines for Traffic Data Programs. American Association of State Highway and Transportation Officials. 1992.
  6. 1 2 "Traffic Monitoring Guide - Policy | Federal Highway Administration". www.fhwa.dot.gov.
  7. "Traffic counting on the roadways of Croatia in 2009 - digest" (PDF). Hrvatske ceste. May 1, 2010. Archived from the original (PDF) on July 21, 2011.

The 1992 Edition of the AASHTO Guidelines is out of date. The current edition is from 2018. The Gary Davis article was published in Transportation Research Record 1593, 1997. the date currently shown in the article is the date of an on-line posting.