justified in requiring considerable precision in its exercise. Kraus & Bros. v. United States, 327 U. S. 614, 621-622.
This'regulation does not prohibit carriage of explosives. It presupposes that they must be transported, and, therefore, attempts to lay down a rule for choice of routings. Petitioner was admonished to avoid congested thoroughfares, places where crowds are assembled, streetcar tracks, tunnels; viadupts and dangerous crossings. Nobody suggests that it. was possible to avoid all of these in carrying this shipment from its origin to its destination, { Nor does the regulation require that all or any one of them be avoided except “so far as practicable.” I do not disagree with the opinion of Chief Justice Hughes and the Court in Sproles v. Binford, 286 U. S. 374, that, in the context in which it was used, “ ‘shortest practicable route’ is not án expression too vague to be understood.” A basic standard was prescribed with definiteness — distance. That ordinarily was to prevail, and, if departed from, the . trucker was to be prepared to offer practical justifications.
But thp regulation before us contains no such definite standard from which- one can start in the calculation of his duty. It leaves all routes equally open and all equally closed. The carrier must choose what is “practicable,” not, as in the Sproles case, by weighing distance against obstacles to passage.' We may, of course, take judicial notice of geography. • Delivery of these goods was impossible except by passing through many congested thoroughfares and either tunnels, viaducts or bridges. An explosion would have been equally dangerous and equally incriminating in any of them. What guidance can be gleaned from this regulation as to how one could with reasonable certainty make a choice of routes that would comply with its requirements?
It is said, however, that definiteness may' be achieved •on the trial because expert testimony will advise the jury as to what routes are preferable. Defects in that solution