Travel Time Reliability Reference Manual/Building Corridors
Constructing a Segment for Analysis edit
TMCs are segments of the roadway, often between interchanges or major intersections on arterials. The travel time data is reported at the TMC level. These segments range in length from less than a mile to several miles long. In order to build a corridor and calculate the travel time, TMCs must be connected. Each TMC is assigned a location code. Details can be found at Next Page → Data Format.
A Google Earth (.kml) file mapping out the TMCs in Iowa, Minnesota, North Dakota, South Dakota and Wisconsin is available here or on Google Maps here .
Typically, a corridor can be constructed by connecting successive TMCs in the positive or negative direction. The TMC numbers increase with the direction of travel along the positive direction and decrease along the negative direction. For example, a corridor in the positive direction might consiste of 107P04585, followed by 107P04586, 107P04587 and 107P04588 etc. In the negative direction, 107N04588 would be the first TMC, followed by 107N04587, 107N04586, and 107N04585 etc.
Longer corridors, however, can be constructed by simply connecting successive TMCs. When roadways intersect other roadways, the TMC sequence may change. Therefore, viewing TMC points in GIS or other mapping software allows one to see the sequence of TMCs along the desired corridor. The static file containing TMC information, includes the roadway name, direction and latitude and longitude coordinates, allowing the points to be plotted in various programs. The NPMRDS data set also includes a shapefile which can be used to construct corridors in GIS.
One difference in the TMC data provided by INRIX, is that TMC points are defined by a beginning and ending latitude and longitude which typically allows a corridor to be constructed by connecting the ending latitude/longitude of one TMC to the beginning latitude/longitude of another.
Once the order and sequence of TMC points along the corridor is defined, travel times and other metrics can be calculated.