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Max Deflection without Horizontal Curve

Max Deflection without Horizontal Curve

Max Deflection without Horizontal Curve

(OP)
This does not seem to be covered in AASHTO, but I’ve seen two equations used to determine the max deflection that can be used without a horizontal curve:

1. arctan(1/design speed)
2. arctan(60/design speed^2)

What is the appropriate criteria & reference to use for this situation?

My application is a 4-lane local road with 35mph design speed.

Thanks.

RE: Max Deflection without Horizontal Curve

In Ohio, ODOT uses equation #1 for high speed (50 Mph and greater) and equation #2 for low speed; rounded to the nearest 15" (ODOT location and Design Manual, Vol 1 Fig 202-1E). For 35 MPH, max deflection will be 2^ 45'

RE: Max Deflection without Horizontal Curve

(OP)
Thanks dficker…do you have a hard reference for those equations (e.g. AASHTO, or something like that)??? My state DOT does not have these equations in there road design manual and I was looking for a reference to back-up the use of these equations.

RE: Max Deflection without Horizontal Curve

You could use the MUTCD taper equations

V > 45 mph     L = WS2/60
V >= 45 mph    L = WS

and plug 1 in for W to give you a rate.

------------------------------------------
     "...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail."

              Wm. Phelps Eno, ca. 1928

RE: Max Deflection without Horizontal Curve

(OP)
ACtrafficengr...I see what your saying.  That must be how the equations I have shown were developed.  So, is that saying that a taper is basically a horizontal deflection w/o a curve?  I think I would agree with that, but it seems like round-a-bout reasoning.  I’m really looking for a more definitive reference.  

Thanks

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