23 CFR § 750.154 - Standards for directional signs.
The following apply only to directional signs:
(a) General. The following signs are prohibited:
(1) Signs advertising activities that are illegal under Federal or State laws or regulations in effect at the location of those signs or at the location of those activities.
(2) Signs located in such a manner as to obscure or otherwise interfere with the effectiveness of an official traffic sign, signal, or device, or obstruct or interfere with the driver's view of approaching, merging, or intersecting traffic.
(3) Signs which are erected or maintained upon trees or painted or drawn upon rocks or other natural features.
(4) Obsolete signs.
(5) Signs which are structurally unsafe or in disrepair.
(6) Signs which move or have any animated or moving parts.
(7) Signs located in rest areas, parklands or scenic areas.
(1) No sign shall exceed the following limits:
(i) Maximum area - 150 square feet.
(ii) Maximum height - 20 feet.
(iii) Maximum length - 20 feet.
(2) All dimensions include border and trim, but exclude supports.
(c) Lighting. Signs may be illuminated, subject to the following:
(1) Signs which contain, include, or are illuminated by any flashing, intermittent, or moving light or lights are prohibited.
(2) Signs which are not effectively shielded so as to prevent beams or rays of light from being directed at any portion of the traveled way of an Interstate or primary highway or which are of such intensity or brilliance as to cause glare or to impair the vision of the driver of any motor vehicle, or which otherwise interfere with any driver's operation of a motor vehicle are prohibited.
(3) No sign may be so illuminated as to interfere with the effectiveness of or obscure an official traffic sign, device, or signal.
(1) Each location of a directional sign must be approved by the State highway department.
(2) No directional sign may be located within 2,000 feet of an interchange, or intersection at grade along the Interstate System or other freeways (measured along the Interstate or freeway from the nearest point of the beginning or ending of pavement widening at the exit from or entrance to the main traveled way).
(3) No directional sign may be located within 2,000 feet of a rest area, parkland, or scenic area.
(i) No two directional signs facing the same direction of travel shall be spaced less than 1 mile apart;
(ii) Not more than three directional signs pertaining to the same activity and facing the same direction of travel may be erected along a single route approaching the activity;
(iii) Signs located adjacent to the Interstate System shall be within 75 air miles of the activity; and
(iv) Signs located adjacent to the primary system shall be within 50 air miles of the activity.
(e) Message content. The message on directional signs shall be limited to the identification of the attraction or activity and directional information useful to the traveler in locating the attraction, such as mileage, route numbers, or exit numbers. Descriptive words or phrases, and pictorial or photographic representations of the activity or its environs are prohibited.
(f) Selection method and criteria.
(1) Privately owned activities or attractions eligible for directional signing are limited to the following: natural phenomena; scenic attractions; historic, educational, cultural, scientific, and religious sites; and outdoor recreational areas.
(2) To be eligible, privately owned attractions or activities must be nationally or regionally known, and of outstanding interest to the traveling public.
(3) Each State shall develop specific selection methods and criteria to be used in determining whether or not an activity qualifies for this type of signing. A statement as to selection methods and criteria shall be furnished to the Secretary of Transportation before the State permits the erection of any such signs under section 131(c) of title 23 U.S.C., and this part.