What is meant by "horizontal clearances" on the NCEES exam outline?

[ptatohed]

On the NCEES exam outline, for the Transportation exam specs (both AM and PM actually), it lists:

"Vertical and/or horizontal clearances".

It's clear to me what vertical clearances are (a vertical curve clearing a pipe below or a bridge above, etc.) but what do you think is meant by horizontal clearances?

http://cdn1.ncees.co/wp-content/uploads/2012/11/PE_CivTrans_-with_1310_-design_-standards.pdf

Thanks.

 

[Troutfinder P.E.]

Horizontal sight offset (HSO) i.e being able to see around a horizontal curve for roadway obstructions etc.

 

[andyrich]

I agree with HSO which is different than stopping sight distance. HSO can be calculated by CERM 79.45 (GDHS 3-38) as a funcion of SSD (S) and R. HSO = R(1-cos(28.65*S/R)

For example a 35 mph design speed and a curve radius of 800', the S is 250 feet. The HSO is then 800(1-cos(28.65*250/800) = 9.74'. If your lanes are 12 foot wide, then you would need to keep objects 9.74 -12/2 = 3.74 feet from the edge of the road.

 

[ptatohed]

Thanks guys.

Andy, the HSO formula in the GDHS is now 3-36 (latest 2011 6th ed). Also, remember that R is the distance from curve center/origin to the center of the inside lane, not the radius of the curve).

Yeah..... I thought about HSO (Horizontal Sight Line Offset) but, to me, that is specifically sight distance which is listed as its own line item on the syllabus (item I F). As for clear zone , that's listed too as its own line item (Roadside clearance analysis, item IV A).

The only thing I can think of are those horizontal curve problems you see from time to time where there might be a tree, rock, house, etc. in the way and they ask you to, say, extend or offset one of the tangents a certain distance to avoid the tree by X' feet. Does that make sense?

 

[MWC PE]

It is either the HSO or the E variable for the horizontal curve equation.

 

[ptatohed]

It is either the HSO or the E variable for the horizontal curve equation.

Thanks MWC. Again, I think HSO is specifically sight distance, not necessarily 'clearance'. I'm not sure what you mean by "E variable"? E = External Distance (From MOC to PI), not really 'horizontal clearance' as I see it (unless maybe you are trying to clear something located at the PI).

The more I thought about it, the more I think I answered my own question. I think horizontal clearance is when a proposed curve would be too close to an existing feature and the problem instructions are to offset/lengthen/shorten the backward/forward tangents to clear the obstacle. I included an example problem (from the NCEES Transpo practice exam).

Does this make sense?

 

[ptatohed]

Here's one (Caltrans LS/LSIT workbook).