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 1 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 the ball-bank indicator, not the calculated value. Examples of ball-bank indicators are shown in the following Figure 2. (See discussion of "Calculated Speed" in paragraph (2) of this subsection).
         Attached Graphic
         

   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 (9) 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) Selection of car and mounting of ball-bank indicator.

      1. (A) Select an average passenger car for making the test runs and mount the ball-bank indicator on the center line of the dash.

         1. (i) Suitable metal strap mountings can be made on which to mount the indicator, as shown in the following Figure 4.
            Attached Graphic
            
         2. (ii) The metal strap holding the right-hand side of the indicator on dash mountings should be slotted and a thumb nut provided so the steel ball can be adjusted to the zero degree position by raising or lowering the right side of the indicator.
      2. (B) If there is any doubt about the selection of an average car, a ball-bank indicator should be mounted on three different makes or year models for a check.

   4. (4) Before conducting test runs. To ensure proper operation of the ball-bank indicator, it is critical that the following steps be taken before conducting test runs.

      1. (A) Inflate all tires to the uniform pressure used during speedometer calibration.
      2. (B) Calibrate the test vehicle's speedometer in accordance with paragraph (5) of this subsection.
      3. (C) Zero the ball-bank indicator (see procedure in paragraph (6) of this subsection).

   5. (5) Calibrating speedometer.

      1. (A) It is essential that speedometers be calibrated accurately so that advisory speeds will be uniform throughout the state.
      2. (B) Calibrate the speedometer for recording of speed. The accuracy of the odometer for recording distance should be checked against a measured distance. Calibration for speed can be done easily with a radar speed meter or by timing the car over a measured distance. The speedometer should be checked for each 5 mile per hour interval over 20 miles per hour, and several test runs should be made for each speed so that an average value may be obtained.

   6. (6) Zeroing the ball-bank indicator.

      1. (A) The ball-bank indicator must be adjusted to the zero reading before test runs are conducted.
      2. (B) This must be done with the car straddling the center line of the pavement on a tangent section to give the effect of a flat level surface, and the driver and recorder in the same position in which they will ride during the test runs. It is essential that the driver and recorder be in the same position when the ball-bank indicator is set to the zero reading as they will be when the test runs are made, because a shift in the load is reflected in a change of the ball-bank indicator reading.

   7. (7) Conducting ball-bank indicator test runs.

      1. (A) The curve should be driven at the calculated speed described in paragraph (2) of this subsection on the initial run.
      2. (B) If the calculated speed is not available, the curve should be driven at an estimated speed approximately 5 miles per hour slower than that which the driver feels he or she can maintain throughout the entire length of the curve.

      3. (C) Each succeeding run should be made at a speed 5 miles per hour greater than the preceding run until the ball-bank indicator reading reaches:

         1. (i) 10 degrees for speeds of 35 miles per hour or more;
         2. (ii) 12 degrees for speeds of 25 and 30 miles per hour; or
         3. (iii) 14 degrees for speeds of 20 miles per hour or less.
      4. (D) On each test run, the driver should reach the test run speed at a distance of at least 0.25 mile from the beginning of the curve and maintain this speed throughout the entire length of the curve. The path of the car throughout the curve should be maintained as nearly as possible in the center of the right hand lane.
      5. (E) Test runs should be made in each direction on each curve.
      6. (F) On each of the speeds of the test runs, the observer must carefully note the position of the ball throughout the length of the curve and record the maximum deflection in degrees. The readings should be interpolated as closely as possible to the nearest degree.

   8. (8) Alternate ball-bank indicator test run method. An alternate procedure, intended to minimize the number of test runs required to determine the speed for which the curve is to be posted, is as follows.

      1. (A) Drive the car at a speed of 5 miles per hour around the curve, staying as nearly as possible in the center of the right hand lane, and record the maximum deflection of the ball-bank indicator in degrees.

         1. (i) Record the reading of the ball-bank indicator as plus if the deflection of the ball is to the right on a right hand curve and to the left on a left hand curve.
         2. (ii) Record the reading of the ball-bank indicator as minus if the deflection of the ball is to the left on a right hand curve and to the right on a left hand curve.

      2. (B) Drive around the curve at a constant speed that can be maintained without acceleration or deceleration and without driving outside the right-hand traffic lane.

         1. (i) Record the maximum deflection of the ball-bank indicator.
         2. (ii) Record the speed at which the curve was driven.
      3. (C) Compute the maximum safe speed for the curve by solving the following formula for V2:
         Attached Graphic
         

      4. (D) Drive around the curve, staying in the right-hand lane, at the calculated speed V2 without acceleration or deceleration as a check on measurements and computations. The ball-bank indication recorded at speed V2 should then be:

         1. (i) 10 degrees for speeds of 35 miles per hour or more;
         2. (ii) 12 degrees for speeds of 25 and 30 miles per hour; or
         3. (iii) 14 degrees for speeds of 20 miles per hour or less.

   9. (9) Selecting speed for posting.

      1. (A) Remember, the speed to be posted shall be based on the results obtained from test runs with the ball-bank indicator (described in paragraphs (7) and (8) of this subsection), 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 the procedures provided in this subsection.
      6. (F) 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.

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.