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. 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. 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. The reading of the ball-bank indicator should be recorded 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. 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. Record the maximum deflection of the ball-bank indicator and the speed at which the curve was driven.
  3. Compute the maximum safe speed for the curve by solving the following formula for V2:
    (click in image to see full-size image)
    where:
    q1
    = maximum ball-bank indicator reading as recorded in Step 2
    q2
    = 10° for 35 mph and greater
    or
    12° for speeds of 21 through 34 mph
    or
    14° for 20 mph and less
    (click in image to see full-size image)
    = ball-bank indicator reading as recorded in Step 1
    V1
    = vehicle speed in miles per hour at which q1 was recorded in Step 2
    V2
    = calculated safe speed in mph for which curve is good.
  4. Drive around the curve, staying in the right-hand lane, at the calculated speed V1
    without acceleration or deceleration as a check on measurements and computations. The ball-bank indication recorded at speed V1
    should then be:
    • 10° for speeds of 35 mph or more
    • 12° for speeds of 25 and 30 mph
    • 14° for speeds of 20 mph or less.