Ignorance of the law no excuse.

In a high court appeal ruling many years ago the lord chief justice made the declaration that Ignorance of the law was no excuse.
This is now widely accepted in court hearings.
However consider the wealth of legislation contained within the use of motor vehicles on the road.
Is it possible for drivers of motorhomes who tow small cars with purpose built A frames to read digest and understand the regulations applicable to their use.
We have now had a revised D of E annual vehicle test that will add to the knowledge that we are all infered to know.
The test itself is an enigma, in as much as it was brought in to ensure that once a year your vehicle would have faults corrected and the examiner charged with a sort of duty to anticipate that the vehicle was capeable of going another year without some major and dangerous defect developing.
Ignorance of the finer print in the construction and use regulations if tested on a wide selection of the driving public would be quite widespread.
The question is if only the lawyers and legislators can fully understand it how can the person driving a vehicle be expected to know and understand it?