1A. Flashing Yellow Dot. Traditionally, a single-section traffic signal consisting of a flashing yellow dot (FYD) is installed for any of several functions:
Because of the FYD's multiple roles, ambiguity can result. In fact MUTCD 4K.3, which allows FYDs for warning and intersection control, recognizes this problem and addresses it with the restriction "Warning Beacons, if used at intersections, shall not face conflicting vehicular approaches.". Otherwise, collisions could result.
For the first two functions in the list above, TFGAP proposes replacing the FYD with a flashing blue dot (FBD); details of this are below. For the third function, TFGAP calls for replacing the FYD with a steady green dot (SGD) as detailed here. TFGAP, if fully implemented, will not only eliminate ambiguity but also free the FYD for a new use, at intersections, for signaling clearance after a flashing green dot (FGD). The overall plan is given here.
1B. Flashing Blue Dot. We call this proposed flashing blue signal a beacon, in a definition narrower than that found in MUTCD section 4K. The MUTCD use of the term includes the flashing red and yellow lights at intersections; but their TFGAP equivalents, flashing red and long-term steady green respectively, are classified as part of static service. Because they are nonetheless similar to beacons, some red and green signals are included in the pictorial examples in later sections of this page.
The color blue has precedent for purposes of warning, appearing on most police cars' flashers, and being used on railroad cars when they must not be moved due to personnel making repairs.
A beacon should never be used alone. Instead, it ought always to be attached to a sign or other device that communicates to the driver exactly what the matter is. The dot shape is always sufficient for the beacon, but in some cases another shape, such as an arrow for a curve, might be supportive. For that signal we write FBN (flashing blue non-dot).
TFGAP does not define the use of a steady blue signal. Some channelizing devices, as used in temporary traffic control, currently have a steady signal as specified in contrasting clauses of MUTCD 6F.58:
1C. Information Management. The vast majority of traffic signs do not need beacons attached to them. Indeed, there are cases where adding a FBD will do more harm than good. Hence this report merely describes how, when planners decide that such signals are necessary, to implement them under TFGAP.
A governing principle is that the most important controls should be the most conspicuous. For instance, a ROUGH ROAD sign must never upstage a STOP sign, and guide signs should be more prominent than tourist attraction signs. Even when displays are well prioritized, drivers may suffer from information overload if too may controls are used; this is why for example specific-service signs (MUTCD 2F) are omitted on stretches of freeway where interchanges are closely spaced.
Particularly in the vicinity of other traffic signals, such as for right-of-way or lane use, beacons on signs may increase confusion more than they increase edification. For instance, instead of adding a FBD to a NO TURN ON RED sign, a better solution is to have a steady red arrow on the right-of-way signal.
If a signal is of a shape other than a dot, drivers must figure out what that shape is and what it is supposed to mean. In order to simplify these tasks, all of the non-dot symbols offered in section 3 below are purely redundant:
1D. A Detailed Example. The ONE WAY regulatory sign, which explains the configuration of a crossing street, embodies a number of subtleties because it is used at intersections. As neither a stop or yield sign, any signal attached to it is merely an attention-getter and should be blue, because red, yellow and green lights have regulatory implications of a completely different nature.
TFGAP recommends the blue signal be a dot instead of an arrow, because a blue arrow that points in the legal direction might suggest to drivers that leaving the intersection by any other direction is wrong. In fact, at most crossings of one-way streets motorists are permitted to go straight. The one case in which the arrow becomes defensible is when the only legal way to leave the intersection happens to be along the one-way street in question.
A blue one-way signal, whether dot or arrow, will still be very close to the intersection and may be distracting. Perhaps better is to install FBDs on the one-way street's DO NOT ENTER signs, which may be a little farther from the intersection than the ONE WAY signs. WRONG WAY signs, if present, will certainly be distant enough as mounting points to minimize confusion.
There are other possibilities. The right-of-way signal can be implemented with arrows, steady or flashing, that point in all the legal directions of travel. Placing ONE WAY signs immediately next to the right-of-way signals will give roughly the same effect as installing the signs elsewhere and adding blue beacons at those locations. Another choice, most helpful at night, is to use an illuminated (MUTCD 2A.08) ONE WAY sign.
Because the following topics involve numerous images, they are presented on separate pages; all signals depicted thereon are flashing. Although signs are pictured with two signals, one may be sufficient. When there are two signals, an open question is whether they should flash alternately or simultaneously.