The vehicle count add on (My Bike Radar Traffic) for the Garmin actually has a number of more useful displays than just summing up how cars have passed you. You need to go into IQ Apps in Garmin Express (with the Garmin attached to the pc), right click on the app and choose Settings (a typical clear as mud Garmin arrangment) and you can pick a number alternative to be displayed, one or more -
Display Approach Speed (Relative)
Display Vehicle Speed (Absolute)
Display Last Vehicle Speed (Absolute)
Display Lap Total