Here's what FAA thinks about it:
8.6.2. RVR Availability and Use Requirements.
8.6.2.1. RVR Availability.
a. For Category II, RVR availability requirements for touchdown zone (TDZ), mid runway (MID), and ROLLOUT RVR (or a corresponding international equivalent location) should be provided for any runway over 8000 ft in length. TDZ and ROLLOUT RVR should be provided for runways less than 8000 ft. Exceptions to this requirement for U.S. Operators at international locations may be approved on a case by case basis by AFS-400, if an
equivalent level of safety can be established. Factors considered due to local circumstances at foreign airports may include minima requested, landing field length requested, characteristics of prevailing local weather conditions,
location of RVR sites or RVR calibration, availability of other supporting weather reports on nearby runways, etc.
b. Aircraft requiring a landing or takeoff distance in normal operation (using operational braking techniques) less than 4000 ft may be approved to use a single TDZ, MID, or ROLLOUT RVR report as applicable to the part of the runway used. For such operations, RVR values not used are optional and advisory, unless the aircraft operation
is planned to take place on the part of the runway where a MID or ROLLOUT RVR is located.
8.6.2.2. RVR Use. In general, the controlling RVR for Takeoff, Landing and Rollout are as follows:
a. Take-off:
(1) Where visibility minima are applicable, visibility must be reported sufficiently close to the takeoff runway to be considered valid or applicable. The determination of acceptability, if not otherwise addressed by FAA, may be determined by the operator or CHDO.
(2) Where RVR minima are applicable, RVR must be reported, and the RVR minimum value is considered to be controlling at each relevant RVR reporting point. The RVR/Visibility representative of the initial part of the take-off may be replaced by pilot assessment. For take-off operations the relevant RVR refers to any portion of the runway that is needed for takeoff roll, including that part of the runway that may be needed for a rejected take-off.
b. Landing.
(1) Where visibility minima are applicable, visibility must be reported sufficiently close to the landing runway to be considered valid or applicable. The determination of acceptability, if not otherwise addressed by FAA,
may be determined by the operator or CHDO. Where RVR is used, the controlling RVR for all Category I operations is the touchdown RVR. All other readings, if any, are advisory.
(2) The controlling RVR for Category II (for Category III see AC 120-28D) with or without rollout guidance control system is the TDZ RVR or equivalent. Mid and rollout RVR are advisory, unless otherwise specified in OpSpecs.
NOTE: An acceptable alternate set of OpSpecs specifying minimum values for MID and ROLLOUT RVRs may be provided for airplanes without a rollout guidance or control system. If determined appropriate by the FAA, and agreed to by the operator, TDZ, MID, and ROLLOUT may be specified as controlling. MID RVR, if relevant, may not be less than 400-ft. (125-meters). ROLLOUT RVR, if relevant, may not be less than 300-ft. (75-meters). For landing operations, the relevant RVR refers to the portion of the runway that is needed for landing down to a safe taxi speed (typically below 60-knots for large turbojet aircraft).
8.6.3. Pilot Assessment of Takeoff Visibility Equivalent to RVR. (See also 4.2. b and c). In special circumstances, provisions may be made for pilot assessment of takeoff visibility equivalent to RVR to determine compliance with takeoff minima. Provisions to authorize pilot assessed RVR is provided through Standard Operations Specifications. A pilot may assess visibility at the take off position in lieu of reported TDZ RVR (or equivalent) IAW the requirements detailed below:
a. TDZ RVR is inoperative, or is not reported (e.g., TDZ RVR inoperative, ATS facility is closed); or
b. Local visibility conditions as determined by the pilot indicate that a significantly different visibility exists than the reported RVR (e.g., patchy fog, blowing snow, RVR believed to be inoperative or inaccurate); and
c. Pertinent markings, lighting, and electronic aids are clearly visible and in service (e.g., no obscuring clutter); and
d. The assessment is made using an accepted method regarding identification of an appropriate number of centerline lights, or markings, of known spacing visible to the pilot when viewed from the flight deck when the
aircraft is at the take-off point; and
e. Pilot assessment of visibility as a substitute for TDZ (takeoff) RVR is approved for the operator, and observed visibility is determined to be greater than the equivalent of 300 RVR (90m); and
f. A suitable report of the pilot’s determination of visibility is forwarded to ATS or to the operator, as applicable (e.g., if an ATS facility is available and providing ATS services, or if the operator elects to receive such reports).
NOTE: A suitable report of a pilot’s determination of visibility provided to ATS or to the operator is intended to facilitate other operations and timely distribution of meteorological information. It is not intended to be a verification of minima or limit or restrict minima for the aircraft making the report.
Why don't we forget all the confusion for a sec and look at the whole ops from the simple pilot's pilots point of view? The operation must be SAFE that's the goal. How can it be achieved? There's no safer means for a manual flight but to have a adequate visual contact with the surroundings ergo see where you gonna roll, fly. That's the reason a minima was invented. At some point (DA, MDA DH whaever) a pilot must identify the environment by visual means to assess the whole situation and to decide what's next. Despite all the fancy technic and installation blah blah blah the pilot plays the pivot role in that decision making hence the option to continue the approach regardless of RVR down to the minima. Nothing else happens with LVTO but instead of DH there's a beginning of takeoff roll position. Same procedure here: look outside and deicide. RVR transmissiomenters don't do anything else but to assess the visibile segment at the very same point. Conversely RVR 200 is reported but upon lineup I only see 5 CL, certainly will I not take off regardless of what the fancy machine reports. To prevent arbitrary decision making regarding how many CL will one need 90 m visual segment was imposed which proved to be adequate to ensure directional control. It's totally natural for the pilot to assess the visual cues and the law maker made a provision for that.
