1. (a) Overview.

   1. (1) Introduction. A discussion of the following types of advisory speeds is included in this section:

      1. (A) curves and turns;
      2. (B) intersections;
      3. (C) narrow and one-lane bridges;
      4. (D) descending grades of six percent or greater;
      5. (E) dips; and
      6. (F) exit ramps.

   2. (2) Advisory speed sign posting.

      1. (A) The W13-1 or SW13-1 ADVISORY SPEED sign may be used in conjunction with any warning sign to indicate the maximum safe speed for passenger cars around a curve or through a hazardous location. It shall not be used in conjunction with any sign other than a warning sign, nor shall it be used alone.

      2. (B) The W13-1 or SW13-1 sign shall always be mounted on the same post and immediately below the warning sign to which it applies.

         1. (i) The W13-1 sign shall be used with warning signs smaller than 36 by 36 inches.
         2. (ii) The SW13-1 sign shall be used with warning signs 36 by 36 inches and larger.
      3. (C) The following Figure shows typical warning and advisory speed signing applications.
         Attached Graphic
         

2. (b) Curves and turns.

   1. (1) Introduction

      1. (A) Horizontal curves having a safe operating speed of 5 miles per hour or more below the posted maximum speed limit should be signed with advisory speed limits.
      2. (B) Vertical curves may also be signed with advisory speed limits.
      3. (C) The speed to be posted will be based on results obtained from test runs in a vehicle equipped with a ball-bank indicator, not the calculated value. The ball-bank indicator can be electric or manual.

   2. (2) Calculated speed.

      1. (A) For curves and turns, the calculated speed is to be used as a guide for making the initial test run and as a check on the speed obtained by the use of the ball-bank indicator. The calculated speed is not, however, to be used as the sole basis for selecting the posted speed. See "Selecting Speed for Posting" in paragraph (3) of this subsection for additional discussion.
      2. (B) Calculate the design speed of the curve under consideration using the following formula.
         Attached Graphic
         

   3. (3) Selecting speed for posting. When there is a reverse curve or a series of three or more curves, the advisory speed sign shall show the value for the curve having the slowest safe speed in the series.

      1. (A) Remember, the speed to be posted shall be based on the results obtained from test runs with the ball-bank indicator, not the calculated value.
      2. (B) The posted speed shall be a multiple of 5 miles per hour.
      3. (C) In selecting the speed to be posted, care should be taken that the calibrated speed for any given speedometer reading is used rather than the speedometer reading itself.
      4. (D) As a final check, the posted speed is aimed at the highest value that will permit the average car to travel around the curve in its own lane without causing an uncomfortable side throw to its passengers.
      5. (E) The speed to be posted on the curve should not be reduced arbitrarily below that determined by ball-bank indicator test runs.
      6. (F)

3. (c) Intersections.

   1. (1) Introduction. Advisory zones may be posted at:

      1. (A) intersections such as traffic circles (only a few of which are left in the state) designed for an operating speed less than the speed of the approaches; and
      2. (B) intersections with restricted sight distances which require a reduction in speed for safe operation.
   2. (2) View obstructions. Trial runs should be conducted to determine the safe and reasonable speed for the area. For intersections having view obstructions, this speed may be posted as an advisory speed below a warning sign to warn motorists of the limited sight distance.

4. (d) Narrow and one-lane bridges.

   1. (1) Introduction.

      1. (A) The following bridges may require advisory speeds:

         1. (i) narrow bridges with clear width between curbs less than 18 feet, but more than 16 feet; and
         2. (ii) one lane bridges with clear width between curbs of 16 feet or less.
      2. (B) Advisory speed zones should be applied for such structures when horizontal or vertical sight distance restrictions on the approaches require a reduction of approach speeds for safe operation.
      3. (C) Advisory speeds of this type are intended to eliminate the element of surprise.

   2. (2) Placement of signs.

      1. (A) The normal location of the W5-2 or W5-2a NARROW BRIDGE or W5-3 ONE LANE BRIDGE signs, under which a W13-1 or SW13-1 ADVISORY SPEED sign would be mounted, is specified in Table 2c-4 of the latest edition of the Texas Manual on Uniform Traffic Control Devices for Streets and Highways.
      2. (B) The signs may be located at a greater distance in advance of the bridge if necessary to allow sufficient time and distance for deceleration and may be repeated at the point where the structure first comes into view.

5. (e) Descending grades of six percent or greater.

   1. (1) Introduction. The posting of advisory speed may be prudent where vehicles may attain a speed in excess of that required:

      1. (A) for a safe stopping distance; or
      2. (B) for safe travel around curves at the bottom or within the limits of the grade.
   2. (2) Determining minimum sight distances. The minimum horizontal and vertical sight distances on descending grades of 6% or greater should be determined either by field measurements or by calculations from the plans.
   3. (3) Calculation. Using the minimum sight distance as the safe stopping distance, the critical speed should be calculated from the following formula.
      Attached Graphic
      

   4. (4) If a curve is involved.

      1. (A) If a curve is within the limits of or at the bottom of such a grade, the advisory speed for the curve should be determined by the procedure found in subsection (b) of this section.
      2. (B) The speed to be posted should be the lower of the two speeds found for providing a safe stopping distance and that for safe travel around the curve.

6. (f) Dips and exit ramps.

   1. (1) Dips.

      1. (A) An advisory speed may be desirable where a depression in the road profile is sufficiently abrupt to:

         1. (i) create a hazardous condition;
         2. (ii) cause discomfort to passengers;
         3. (iii) cause a shifting in cargo; or
         4. (iv) deflect a vehicle from its true course when crossed at speeds prevailing on the approaches.

      2. (B) The speed to be posted for dips should be determined by trial runs. It should be the highest speed that will enable a vehicle to travel over the dip:

         1. (i) without considerable discomfort to passengers;
         2. (ii) without causing a shifting of cargo; or
         3. (iii) without causing a deflection of a vehicle from its true course.
   2. (2) Exit ramps. The Exit Speed or Ramp Speed signs (W13-2 and W13-3) are intended for use where engineering investigations of roadway, geometric, or operating conditions show the necessity of advising drivers of the maximum recommended speed on a ramp.

Source Note:The provisions of this §25.25 adopted to be effective February 17, 2000, 25 TexReg 1151; amended to be effective December 9, 2004, 29 TexReg 11389; amended to be effective March 16, 2006, 31 TexReg 1728.