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Single lane or dual lane considerations
Figure 7 shows a typical single lane configuration. However, with the Drive5's higher 5-megapixel
resolution and 1-inch sensor format, it can cover up to two lanes of traffic. The Drive5's lens is
adjusted during installation to create the following conditions:
Standard for US style of plates: 135 pixels across a 1 foot wide license plate placed 2 feet above the
ground level at the nominal trigger position (ground loop, laser, etc.). With typical US lane coverage
(14'), the Drive5 will yield ~180 pixels/plate. If maintaining 135 pixels per plate, the lane coverage is
now 18'.
Standard for European style of plates: 140 pixels across a 50 cm wide license plate placed 60 cm
above the ground level at the nominal trigger position (ground loop, etc.). The coverage is now up to
9 meters, which can definitely cover two lanes (see Figure 8 below).
Typical overhead site layout – dual-lane coverage (with optional external flash unit)
Figure 8.
Camera tilt considerations
The requirement to freeze the motion of high-speed vehicles limits how steep or shallow the tilt angle
of the camera may be. For example, it is important to prevent the horizon from appearing in the
image, and thereby allowing the sun to blind the camera. For over lane installations, a camera tilt
between 20° to 30° is recommended, with 25° being considered the optimal angle. This angle of tilt is
the best compromise between minimizing visibility blockages caused by closely spaced vehicles and
maximizing plate visibility for plate mounts that are slightly recessed or tilted downwards.
Asynchronous triggering considerations
An embedded vehicle detector is employed to cause the camera to capture an image at the precise
moment the vehicle is in the best position to image both the vehicle and its license plate. If an
external triggering device is used (i.e., ground loop or laser) the delay between the time the vehicle
passes the trigger position on the road and when the trigger signal actually reaches the Drive5 must
be kept to a minimum to prevent high-speed vehicles from moving out of the area viewed by the
camera before the image is snapped.
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