Faced with this in a local law, I went to court, and didn't argue constitutionality, nor legislative intent. Rather I argued practical difficulty.
I will not elaborate more, because I do not understand law, in this instance, well enough to do so. But for the lower court, it worked and the state did not appeal the matter.
Addendum: Let me give an example which my research came up with when preparing my case.
Issue: When a vehicle is stopped to discharge a passenger, must the driver remain at the controls, while the passenger is being discharged? The zone permits stopping for loading and unloading [of passengers, cargo]. In this instance, a passenger is a 92 yo female who needs assistance entering and exiting the vehicle, but is capable of self-ambulating.
Rules: A loading zone exists to load and unload passengers, and a motor vehicle may not remain in the zone for any longer than is required to actively load or unload the motor vehicle. A stopped motor vehicle must have a driver at the controls, otherwise the vehicle shall be deemed parked. Also, a driver may not leave a motor vehicle engine running when the driver is not at the controls.
Analysis: It is normal practice for medical transport drivers to provide assistance to mobility limited passengers, and such assistance is essential to safety and efficiency at locations like train stations and airports when discharging or onboarding passengers. While the strict interpretation of stopping may not apply if the driver leaves the controls for purposes of assisting a passenger, it is the most efficious manner to assure that the rider's needs are being met, and that they safely board and unboard the motor vehicle. Furthermore, if mobility impaired riders were forced to use other loading locations, then they would normally be required to ambulate further, from a more distant location. [Or in the alternative, the majority of people would have to travel further to load and unload, to make a more desirable location available for mobility impaired passengers.] (Also included in the argument/analysis was much about ADA, state disability laws, equal access, etc.)
Conclusion: Where a mobility impaired passenger, who needs assistance boarding or unboarding a vehicle, the driver of that vehicle is most familiar with their needs and can efficiently assist the rider. This is commonly done by bus drivers, and provided for under the city transportation rules for bus drivers. Therefore, in the case of automobiles and other motor vehicles, there is practical difficulty, if the driver does not temporarily abandon the vehicle controls, and assist the passenger. To not do so, may require replanning of loading zones, inconveniencing the majority of passengers, and may violate the rights of mobility impaired passengers, in likely violation of ADA and state laws.
Result: County court ruled that assistance to passengers when stopping to load and unload passengers did not violate motor vehicle code regarding stopped vehicles.