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Superelevation Notes PDF

The document discusses superelevation transitions on circular curves and spirals. It defines terms like runoff, runout, and provides steps to determine superelevation lengths. Runoff is the length to transition from normal crown to full bank, and runout is the reverse transition. For circular curves, 0.7 of runoff occurs before/after the PC/PT, and 0.3 of runoff is on the curve. The document gives an example problem calculating runoff and runout lengths for a 4-lane roadway.

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310 views14 pages

Superelevation Notes PDF

The document discusses superelevation transitions on circular curves and spirals. It defines terms like runoff, runout, and provides steps to determine superelevation lengths. Runoff is the length to transition from normal crown to full bank, and runout is the reverse transition. For circular curves, 0.7 of runoff occurs before/after the PC/PT, and 0.3 of runoff is on the curve. The document gives an example problem calculating runoff and runout lengths for a 4-lane roadway.

Uploaded by

joy lopez
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Superelevation

Objectives
 Know how to determine superelevation transitions on simple
circular curves and spirals
 Know how to use maximum relative gradients to determine
superelevation length transitions
Superelevation
 Used to partially overcome the centrifugal force on a
vehicle as it goes around a curve
 Transition lengths are needed to change the cross slope
from normal crown to full bank and then back down to
normal crown

 There are various methods for transitioning pavement


from normal crown to a superelevated section
 The most common method is to rotate the pavement
around the centerline (which is also the HCL and
TGL)
Runoff
 Runoff is the distance used to change the section from where
the adverse crown is removed (to level) to the point where full
superelevation is achieved
 Runoff length is also the length of spiral length
 Refer to Exhibit 5-15 to get the length (function of e, design
speed and number of lanes rotated)

Runout
 Runout is the distance used to change the section from normal
crown to where the adverse crown is removed (to level)
Circular Curves
 Runout also occurs on the tangent
 0.7*Runoff occurs before the PC and after the PT
 0.3*Runoff occurs on the curve (right after the PC and right
before the PT).
 The circular arc is not fully superelevated because part of the
transition falls on the curve

Spirals
 Runout occurs before the TS (on the tangent) and after the
ST
 Runoff occurs on length of spiral
 There is full superelevation between the SC and CS
Runoff
 Refer to Exhibit 5-15 of HDM to get the length (function of e,
design speed and number of lanes rotated)
 Runoff length is also the length of spiral

Determining Runout Lengths


 Rout=(Roff*NC)/e
 NC is normal crown (usually 2%)
 e is the superelevation rate (%)
Basic steps
 Determine e, Roff
 Calculate Rout
 For circular curves calculate 30% and 70% of Roff
 Draw diagram working back and forth from the PC/PT or
TS/SC
Example
 4-lane roadway (undivided) ---2 lanes rotated
 Design speed=110 km/hr
 Emax=6%
 Radius=3,493 m
 PC STA 1+268
 PT STA 1+826
 Curves to the LT
Step 1 (find e, runoff, runout)
 e=RC (2%)-remove adverse crown (table 2-13)
 Roff=26 m (Exhibit 5-15)
 Rout=(Roff)(NC)/e=(26m)*(2%)/2%=26 m
Step 2 (.7 & .3 Roff)
 0.3*26m=8 m
 0.7*26m=18 m
Step 3 –
Draw
Diagram

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