What is the test for determining whether a defendant's right to access is substantially impaired?

"The determination of whether such substantial impairment has been established must be reached as a matter of law. The extent of such impairment must be fixed as a matter of fact. The cases have consistently held that the trial court must rule, as a matter of law, whether the interference with access constitutes a substantial or unreasonable impairment. Thus in People v. Ricciardi, supra, 23 Cal.2d 390, 402-403, we said: `It was . . . within the province of the trial court and not the jury to pass upon the question whether under the facts presented, the defendants' right of access will be substantially impaired. If it will be so impaired the extent of the impairment is for the jury to determine. This is but another way of saying that the trial court and not the jury must decide whether in the particular case there will be an actionable interference with the defendants' right of access."