Sensors to detect vehicle height from the side
Try this







simulate this circuit &ndash; Schematic created using CircuitLab

Offset the two sensors by 6". This allows the Range^2 and (Range+6")^2 to give you some useful distance information.

The two diodes after the photodiodes will generate the LOG (beware, temperature sensitive) and greatly extend the dynamic range.

Have one of these every foot of vertical distance.