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Caltrans manages more than 50,000 miles of California's highway and freeway lanes, provides inter-city rail services, permits more than 400 public-use airports and special-use hospital heliports, and works with local agencies. Caltrans carries out its mission of providing a safe, sustainable, integrated and efficient transportation system to enhance California’s economy and livability, with six primary programs: Aeronautics, Highway Transportation, Mass Transportation, Transportation Planning, Administration and the Equipment Service Center.

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Caltrans Traffic Volumes

Traffic Volumes (also known as Traffic Counts) are surveyed from the California State Highway network. The data originated from Caltrans Traffic Census database compiled by Caltrans Districts Offices. The Districts calculated the volumes hourly, daily, and monthly to derive an annual average daily traffic count. Volumes are surveyed in both directions, "Back" describes southbound and westbound and "Ahead" describes northbound and eastbound.

Data and Resources

FieldValue
Publisher
Modified Date
2018-03-27
Release Date
2016-08-11
Frequency
Annually
Homepage URL
Identifier
59ffffb0-06e4-4538-a695-736e1844f241
Spatial / Geographical Coverage Area
POLYGON ((-124.28833007812 41.992160233376, -124.25537109375 41.869560826995, -124.34326171875 41.869560826995, -124.0576171875 41.557921577804, -124.15649414062 40.94671366508, -124.29931640625 40.613952441167, -124.48608398438 40.388396873884, -124.24438476562 40.136890695346, -123.82690429687 39.715638134796, -123.71704101562 38.891032826488, -123.16772460938 38.453588708941, -122.96997070312 38.160476280996, -123.046875 37.987504371064, -122.72827148438 37.892195547244, -122.51953125 37.675125278921, -122.50854492188 37.509725842938, -122.39868164062 37.361425501905, -122.42065429688 37.186578595249, -122.18994140625 36.932330061503, -121.8603515625 36.914764288956, -121.78344726562 36.738884124394, -122.01416015625 36.615527631349, -121.904296875 36.297418186508, -121.22314453125 35.612650818757, -120.95947265625 35.398005947151, -120.88256835937 35.308401401692, -120.849609375 35.191766965947, -120.64086914062 35.083955579276, -120.64086914062 34.642247047769, -120.46508789062 34.470335121217, -119.53125 34.406909656521, -119.30053710938 34.179997586881, -119.19067382812 34.098159345216, -118.7841796875 34.016241889667, -118.49853515625 34.016241889667, -118.46557617187 33.897777013859, -118.48754882812 33.77001515278, -118.33374023438 33.706062655101, -118.11401367188 33.742612777347, -117.79541015625 33.541394668983, -117.34497070312 33.201924189779, -117.19116210938 32.741082231501, -117.12524414063 32.55607364492, -115.91674804688 32.630123006707, -114.697265625 32.694865977875, -114.48852539062 33.587167339047, -114.49951171875 34.016241889667, -114.169921875 34.307143856288, -114.55444335938 34.723554927042, -114.67529296875 35.020999701115, -120.05859375 39.027718840212, -119.970703125 41.967659203678))
Spatial / Geographical Coverage Location
State
Temporal Coverage
Monday, January 1, 2007 - 09:00 to Sunday, January 1, 2017 - 07:59
License
Other (Public Domain)
Author
Caltrans
Data Dictionary

Caltrans District ID Number: These are California counties that are grouped together predetermined by Caltrans to represent a Caltrans District and identified through a number.
• See District map for more information.

Route Number: A numeric designation to a stretch of roadway to distinguish it from other routes.

Route Suffix: Letter designation after route number.
• See Route Suffix Chart for more information. Some locations may not have a value for this field.

County: Geographic subdivisions of the State of California.
• See County Chart for more information.

Postmile Prefix: Letter identifier before postmile number.
• See Postmile Prefix Chart for more information. Some locations may not have a value for this field.

Postmile Number: Each profile breakpoint is identified by the postmile value corresponding to that point on the highway. The postmile values increase from the beginning of a route within a county to the next county line. The postmile values start over again at each county line. Postmile values usually increase from south to north or west to east depending upon the general direction the route follows within the state.

Postmile Suffix: Letter identifier after postmile number signifying a revision of postmile location.
• See Alignment Field Chart for more information. Some locations may not have a value for this field.

Description of Location: General location description of traffic volume.

South or Westbound Peak Hour: South or westbound is the general direction of traffic flow along the route. Typically in Caltrans this would be described as “Back” Peak Hour. Peak hour usually represents an estimate of the heaviest traffic flow, which usually occurs between 7 to 9 AM and 5 to 7 PM. In urban and suburban areas, the peak hour normally occurs every weekday. On roads with large seasonal fluctuations in traffic, the peak hour is the hour near the maximum for the year but excluding a few (30 to 50 hours) that are exceedingly high and are not typical of the frequency of the high hours occurring during the season.
• See Back and Ahead Leg Explanation of Traffic Counts for more information.

South or Westbound Peak Month: South or westbound is the general direction of traffic flow along the route. Typically in Caltrans this would be described as “Back” Peak Month. Peak month is the average daily traffic for the month of heaviest traffic flow, usually July or August. This data is obtained because on many routes high traffic volumes, which occur during a certain season of the year, are more representative of traffic conditions than the annual average daily traffic.
• See Back and Ahead Leg Explanation of Traffic Counts for more information.

South or Westbound Annual Average Daily Traffic (AADT): South or westbound is the general direction of traffic flow along the route. Typically in Caltrans this would be described as “Back” AADT. The annual average daily traffic (AADT) usually represents the total volume for the year divided by 365 days.
• See Back and Ahead Leg Explanation of Traffic Counts for more information.

North or Eastbound Peak Hour: North or eastbound is the general direction of traffic flow along the route. Typically in Caltrans this would be described as “Ahead” Peak Hour. Peak hour usually represents an estimate of the heaviest traffic flow, which usually occurs between 7 to 9 AM and 5 to 7 PM. In urban and suburban areas, the peak hour normally occurs every weekday. On roads with large seasonal fluctuations in traffic, the peak hour is the hour near the maximum for the year but excluding a few (30 to 50 hours) that are exceedingly high and are not typical of the frequency of the high hours occurring during the season.
• See Back and Ahead Leg Explanation of Traffic Counts for more information.

North or Eastbound Peak Month: North or eastbound is the general direction of traffic flow along the route. Typically in Caltrans this would be described as “Ahead” Peak Month. Peak month is the average daily traffic (ADT) for the month of heaviest traffic flow, usually July or August. This data is obtained because on many routes high traffic volumes, which occur during a certain season of the year, are more representative of traffic conditions than the annual average daily traffic (AADT).
• See Back and Ahead Leg Explanation of Traffic Counts for more information.

North or Eastbound Annual Average Daily Traffic (AADT): North or eastbound is the general direction of traffic flow along the route. Typically in Caltrans this would be described as “Ahead” AADT. “Ahead” describes the direction of traffic flow going northbound or eastbound. The annual average daily traffic (AADT) usually represents the total volume for the year divided by 365 days.
• See Back and Ahead Leg Explanation of Traffic Counts for more information.

Location: Displayed as decimal degrees in latitude and longitude. The lines extending around the Earth horizontally are called latitude. They measure how far north or south an object is on the Earth. The lines running vertically around the Earth are called longitude. These lines measure how far east or west an object is.

Contact Name
Division of Traffic Operations, Office of Performance, Traffic Data Branch
Contact Email
Public Access Level
Public