Roadway Design Question and Answer Forum
Criteria
Question:
I am using PGL chains to draw cross sections. Why are the cross section grade point elevations not matching the proposed
profiles?
Answer:
This is a common mistake Designers make when using PGL chains in Criteria. The way the shape clusters are defined determines
which profile station is applied. Here is the COGO data for cross section 190+00 -L-.
You have -L-, -LL- (left), and -LR- (right) chains and LLPRO and LRPRO profiles. If you defined the shape cluster like
below, then LLPRO profile station is off the -L- baseline, 190+00. This is incorrect.
The way Criteria reads this shape cluster definition is to apply profile LLPRO to the station off baseline L, which is
190+00 and an undesired grade point elevation of 729.4986' (exactly matches the COGO data)
What is desired is at cross section 190+00 -L-, the grade point elevation on the left shape cluster should be 729.7730'
(LLPRO profile and corresponding -LL- baseline station of 189+81.83). To do this, first set the Geopak shapes to
have the same parameters as this shape cluster definition.
Processing the modified shape file and Criteria input file now yields the desired grade point elevation, ~ 729.7730'.
See COGO data above for confirmation.
It is important to note that the shape cluster profile is applied to the stationing of what is defined in shape cluster
baseline statement. For PGL chains with there own profiles, it is never the centerline or the baseline of the green
cross section cell, e.g. L.
