How we obtain various types of traffic data
Centerline mile is a term for one mile of a single roadway, regardless of the number of lanes. (If a road is divided, mileage is not doubled.) MnDOT currently uses ascending route mileage along roadways as the distinction of centerline. This will change in the future when a new Linear Referencing System is more fully implemented. Lane mileage refers to a multiple of continual driving lanes and centerline mileage. For instance, one mile of a road with six continual lanes equals six lane miles.
The various Miles and Lane Mileage reports are produced using records extracted from roadway characteristics. In order to provide consistent figures, the reports are run against a "snapshot" of the database taken every mid-year. The statistics remain constant until a new snapshot is taken. The following are criteria for Roadlog record selection:
- Geographic Area (statewide; by county, municipality, MnDOT Construction District, or Area Transportation Partnership)
- Route Type (ie. Trunk Highways - Interstates, U.S. Highways, and Minnesota State Highways; Local Roads - County State Aid Highways, County Roads, Municipal State Aid Streets, Municipal Roads, Township Roads)
- Other criteria as needed (roadway surface types, divided/undivided roadways, functional classes, etc.)
If lane mileage is requested for a report, the number of continual driving lanes are extracted and calculated according to the individual data item values in each of the combinations of groupings. Then, those values are multiplied by the centerline mileage figures. Temporary lanes (such as turn lanes) are not taken into consideration nor are lanes on ramps or in auxiliary areas (such as rest areas). If the roadway is divided, continual driving lanes are counted on both sides of the roadway.
Vehicle Miles Traveled (VMT) is calculated by multiplying average annual daily traffic (AADT) by the centerline mileages of each roadway segment under consideration. Heavy commercial VMT (HCVMT) can also be calculated by using estimates of commercial truck volumes. HCVMT is only produced for Minnesota's trunk highway system, so historical trends for heavy commercials are only available on Interstate, U.S., and State Highways. VMT figures are used by MnDOT to measure the demand on the transportation network. When VMT and centerline mileage statistics are grouped to form a report, up to three inter-related groupings can be specified. Also, individual values can be grouped to provide combined values, such as combining values for all trunk highways. To provide consistent figures, VMT reports are run against a "snapshot" of the database taken every mid-year. The statistics remain constant until a new snapshot is taken. View the most recent VMT reports on our Data Products page.
The statewide Trunk Highway Log Point report lists landmarks that intersect the various Interstate, U.S. Highway, and Minnesota State Highway routes, in sequential order based on their true mileage. These features include other roadways, bridges, rail grade crossings, municipal and county boundaries, and Construction District boundaries. The listings are based on the most current information available and include such descriptive columns as:
- Route System
- Route Number
- Reference Points
- Description of intersecting features
- Actual centerline mileage to the intersecting features (ACCUM Miles column)
- Construction District
- Most recent traffic volume (AADT)
In addition to centerline mileage, the Log Point report includes a second type of measure called reference points. Reference points are based on reference posts (formerly “mile posts”) which are numbered signs physically located on the side of the road at approximately one mile intervals. Each reference post is, in turn, related to a route true mileage. The relationships and translations between these measures are computer calculated. Reference points are used to provide a type of locational stability. Route true mileage is simply odometer mileage along a route, which starts at zero for each individual route. True mileages along a route may change over time (due to realignments, for example) while events tied to a reference post/point remain fixed. The statewide True Mileage file contains information on the actual centerline mileage for each reference post along Minnesota's trunk highways.
MnDOT's Construction Project Log is a quick visual history of trunk highway road construction and maintenance over time-- the “what, when, and where” guide to field work that has been done since the original construction of the road. Each Project Log has start and end limits illustrated by a straight line map located at the top of the page. The individual project limits themselves are described by horizontal lines located within some portion of that map. Each project is dated along the left side of the page along with a brief description of the work involved, the SP number, year of construction, width and depth of surfacing, material type, etc. Project logs are organized by county and by district, and then by control section.
Since it normally includes only mainline work, information on ramps, roadside work, turn lanes, temporary and bypass construction, median barriers and bridge maintenance work is not included. Also, the project log is not intended to be a source of information for bridge details. Bridge construction and replacements are usually included in or tied to mainline grading and surfacing projects. Finally, not all highways sections have project logs. If the road was initially constructed by a different road authority and then handed over to MnDOT afterwards, a log is generally not available. If a roadway section was originally built by MnDOT, a project log should be available.
Functional classification is the grouping of streets and highways into classes or systems according to the character of service they are intended to provide. When classification changes are made, the roadways are reviewed for possible State Aid system inclusion. When changes occur, roadway revisions and the basemap line work and online maps are updated to portray the physical change to the facility. MnDOT's Functional Classification page provides a comprehensive look at the change process, FHWA requirements and guidelines, maps and other resources.
State highways are divided into segments called control sections for record keeping, maintenance, construction, and other administrative purposes. The four-digit control section number is composed of the two-number county code and an identifying two-digit number within that county. Control sections are revised due to jurisdictional transfers (typically from state to county) when new highway segments or entirely new state highways are built.
Statutory routes are composed of constitutional and legislative routes. In Minnesota, legislative routes are highway numbers defined by the Minnesota State Legislature. The legislative routes numbered 1 to 70 are constitutional routes, defined as part of the Babcock Amendment to the Minnesota State Constitution in 1920, and cannot be altered or removed without a Constitutional amendment. Legislative routes with numbers greater than 70, on the other hand, can be added or deleted by the legislature.
View the latest Control Section Report and maps displaying control sections, statutory routes, and memorial routes on the Data Products page.