The recent decision of the Supreme Judicial Court of Massachusetts in the case of Commonwealth v. Ober has brought to the fore a serious administrative problem arising out of the enforcement of traffic regulations. The problem is particularly acute in the illegal parking cases. Here it is usually impossible for the policeman to do more than tag the car, take down its registration number, and institute proceedings against the registered owner. The difficulty also often occurs in many other situations such as driving through red lights or stop streets where the offense is observed by a patrolman standing near by who is unable to give chase and arrest the driver. If the owner in these cases, when prosecuted, should demand a trial, the only evidence which the state has is that a vehicle bearing a certain number was used in committing a violation of the traffic laws, and that according to the records, the ,defendant is the owner of that vehicle. This evidence, in the absence of statutory provisions regarding its sufficiency, is clearly insufficient, since it does not connect the defendant with the offense. To enforce the traffic laws under such circumstances would necessitate police forces many times the size of those maintained at present, and even then a large number of violators would slip through the meshes of the legal net because of the inability of the prosecuting policeman to identify the operator. To remedy this situation, three, or perhaps four, methods seem to be in use: (1) Enactments making the registered owner absolutely liable, including those providing for towing away and impounding illegally parked cars; (2) Enactments penalizing the owner or other person who permits or suffers his vehicle to be used in a traffic offense; (3) Statutes making the registration number prima facie evidence that the registered owner was operating the vehicle at the time of the offense. It is proposed here to discuss the problems arising under each of these types of enactments.