The City of Toronto (formerly the Regional Municipality of Metropolitan Toronto) began collecting detailed information on the type and volume of traffic crossing selected points on the road system in 1975.  The counting locations were selected such that screen lines or cordon lines could be defined and the counting program has continued on a regular basis since that time, usually twice in a five year cycle.  Subsequently, other regions began similar programs. Given the number of regions with a similar program, they began coordinating their count programs and defining a common set of data standards.  Participating agencies include the City of Toronto, the Regional Municipalities of Durham, Halton, Peel and York and the Ministry of Transportation Ontario. Each region has their own set of needs and priorities for the data. Therefore, the data collection methods are somewhat different in each jurisdiction.  In 1998 the Data Management Group assembled these traffic counts in a common database structure.  Traffic counts have been collected every 3 years across the Greater Toronto Area in the May and June period since 1998 and an online software, Cordon Count Data Retrieval System, was developed to access the data. The last cordon count was conducted in 2014 and the data have been added to the central database.

Descriptions of the cordon count stations and maps, and descriptions of the screen lines by region are available here.
A detailed description of all databases can be found here.