What it the "Ball Bank Indicator" and what does it measure?

'What Is' type questions related to highway safety, accident reconstruction and vehicle simulation
MSI
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What it the "Ball Bank Indicator" and what does it measure?

Post by MSI »

The term "Ball Bank Indicator" refers to an inclinometer that is used for the specific purpose of determining safe (uniform advisory) curve speeds for horizontal curves.
  • It measures the overturning force (side friction), measured in degrees, on a vehicle negotiating a horizontal curve - whether it is an isolated curve, multiple "S" curve, or a ramp to/from a freeway.
  • Typically used by the Department of Transportation and other advisory transportation agencies.
  • Some FHWA research McHenry Software did with Jack Leisch & Associates (JEL) in the 80's was on highway curve design, etc and included an investigation of what the ball bank indicator actually measures.
The following is from Simulation Models of Vehicle Dynamics by McHenry from the TRB Circular "Beyond the Green Book"
  • The “discomfort factor" is representative of the resultant acceleration that an occupant experiences during a recovery maneuver (Fig.4 see below).
  • The use in the evaluation of cornering maneuvers of a hard mounted accelerometer measurement of lateral acceleration of the vehicle does not include the effects that the vehicle roll angle has on the occupant.
    • For example, a vehicle in a normal cornering maneuver rolls in a direction opposite to the turn (I .e., rolls positive, or right for a left hand turn & visa versa) and therefore the “discomfort” which would be experienced is greater than the calculated lateral acceleration (i.e., V2/R).
    • Curves are super-elevated to reduce or reverse the magnitude of the vehicle roll angle to reduce the “discomfort factor" felt by the driver and occupants.
  • Many of the earlier geometric design criteria standards were based on experimental measures of a ball bank indicator during cornering maneuvers which essentially measured the same resultant acceleration as the HVOSM calculated "discomfort factor:
    • The 'discomfort factor- output of tbe HVOSM illustrated the problems associated with cross-slope breaks on highway curves in HVOSM Studies of Highway Cross Slope Breaks on Highway Curves, which was also prepared as a part of the JEL study.
    • In that study the problems associated with cornering on an adversely super-elevated curve (i.e.. cross-slope break) were demonstrated by examination of the “discomfort factor."
    • Subsequent recommendations were made to reduce excursions onto the shoulder breaks which may result in unacceptable levels of driver “discomfort".
ball bank.jpg
ball bank.jpg (59.21 KiB) Viewed 7444 times
Sept 2021 update: replaced the figure with one at better resolution
      • NOTE: the lateral component of gravity is Sin(PHI)
        • where PHI is the vehicle roll angle/roadway slope angle
        • and there may be a difference between the vehicle roll angle and roadway slope due to suspension response of the vehicle, but generally approximately the same
      • NOTE2: for small angles, generally less than 15-20 degrees, the sine of the angle is approximately equal to the angle in radians

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