Using radar on a bridge over traffic

The higher the bridge from the traffic lane the greater the error, just like the greater the distance the radar off the road the greater the error. The greater the [b]distance the radar is off the road and/or above the road[/b], the greater the error.

For [b]stationary radar[/b] the error always causes measured speed to read low. Also the greater the distance off and/or above the road, the greater the radar [b]minimum range[/b] (vehicles at or closer than minimum range cannot be measured by the radar).

The error varies with distance from road, target vehicle speed and range from radar, and radar integration time.

FOR EXAMPLE;
Target Vehicle Speed = 60 mph (97 km/hr)
Radar Distance off Road = 35 feet (10.7 meters)
Radar Integrations Time = 0.3 seconds (300 milliseconds)

RESULTS IN a minimum range of [b]146 feet[/b] (45 meters) 1.66 seconds before vehicle even with radar (0 range). Vehicles closer than 146 feet (48.7 yards) from the radar cannot be measured.

I have been told for a radar to get an accurate reading the radar should be as close to the road as possible. Does this mean if I set up a radar from the top of a bridge pointed at traffic under the bridge I will get an accurate reading? After all I am directly above the center of the lane I am measuring speed.