Hitch Mounted Bike Racks
I have a question about rear hitch mounted bike racks which are readily available in stores. We use one with 4 bikes on it for our family and when the 4 bikes are loaded they obstruct the view of the rear licence plate, brake lights and turn signals. The corner lights can be seen through the spokes of the bike wheels but not clearly. Any opinion on this because these are widely used?
You seem to have described the problems associated with this type of bicycle carrier clearly yourself.
The rear lamps "must not be shielded, covered or obscured by any part of the vehicle or load or by dirt or other material" to quote the Motor Vehicle Act Regulations. The hazard might be greatest during the day when bright sunlight coupled with this obstruction prevents the brake lights from being visible to a driver following you. The resulting rear end collision would certainly be considered to be at least partially your fault.
With regard to the license plate, it must also "be kept entirely unobstructed and free from dirt or foreign material, so that the numbers and letters on it may be plainly seen and read at all times."
Before you scrap the rack or sell it to some other unsuspecting purchaser, it could easily be made legal again. Moving the license plate to the back of it along with duplicating the lights that are obstructed on the vehicle would not be expensive or difficult to do.