Freeway Speeds Colored dots alongside Oakland County freeways at detector locations represent actual freeway congestions based on vehicle speed detectors. Speed detectors are part of the Michigan Department of Transportation's (MDOT) freeway management system. The information that is transmitted from MDOT's system to the RCOC map is displayed to you in five colors, representing the following congestion level and miles-per-hour ranges: Heavy  (1  -  18 MPH) Moderate   (19 - 32 MPH) Light   (33 - 48 MPH) None     (49 - 98 MPH) No information Click on an MDOT freeway speed icon to see the current average speed at that location. The last update date and time are also displayed so you'll know that the data is OK.