Horizontal Curve?

I have worked horizontal layout questions where the stationing is assumed to run down the tangents and others where the stationing is assumed to run along the curve. Which is a better assumption?

Seems like as soon as I assume one, I hit a question where the other method of stationing is assumed.

ALBin517 v2.0 said:

I have worked horizontal layout questions where the stationing is assumed to run down the tangents and others where the stationing is assumed to run along the curve. Which is a better assumption?
Seems like as soon as I assume one, I hit a question where the other method of stationing is assumed.

Click to expand...

Curve stationing is based off where the PI or PC location is. If you are given a PI station you subtract the tangent length to get the PC location and add the curve length of to PC station to to get stationing along the curve. So the station is along the the curve not along the tangent. This is the way I understand it and have been working problems.

Hope that helps.

I agree with North. Many times the problem gives a station at the PI, and you need to calculate T to find the starting station. In horizontal curves, the distance is measured along the curve (the same as your car's odometer would measure it) <-- according to some source I read.

ALBin517 v2.0 said:

I have worked horizontal layout questions where the stationing is assumed to run down the tangents and others where the stationing is assumed to run along the curve. Which is a better assumption?

Seems like as soon as I assume one, I hit a question where the other method of stationing is assumed.

Click to expand...

Stationing will increase along the alignment, up to the BC of the horizontal curve. The BC is the last location on the roadway alignment that will have the same station as the back tangent. From the BC, stationing will continue around the curve, to the EC, and then continue increasing along the forward tangent of the alignment, after the EC. For instance, if the station at the BC is 10+50 and the length of the curve, L, is 850', then the station at the EC will be 1050 + 850 = 19+00. The station also will increase from the BC to the PI along the back tangent, T. The tangents, T, and the PI are imaginary for layout purposes only and are not part of the actual physical roadway alignment. If the tangent, T, was, say, 500', then the station at the PI would be 1050 + 500 = 15+50. The forward tangent between the PI and the EC is not stationed.

Sta EC = Sta BC + L

Sta BC = Sta EC - L

Sta BC = Sta PI - T

Sta PI = Sta BC + T

I am working on a problem in the NCEES Transpo Exam (quest 526). The question is about min shoulder width for two lane (11ft lanes) with concrete barriers and 40mph speed limit and curve radius of 600. Is the horizontal curve radius always the center-line of the inner most lane?

sliq786 said:

I am working on a problem in the NCEES Transpo Exam (quest 526). The question is about min shoulder width for two lane (11ft lanes) with concrete barriers and 40mph speed limit and curve radius of 600. Is the horizontal curve radius always the center-line of the inner most lane?

Click to expand...

My apologies, The question is. Is the horizontal curve radius given always from the center-line of the inner most lane? Regardless of how many lanes

Post the whole problem if you can ..... barriers typically come into play when you do not have the required clear zone for the highway. I'm curious how this question is worded.

....but except for the HSO equation, HC radius is typically the design CL of the road .... someone correct me if I'm wrong here.

You're correct John. Unless you have a divided highway, the radius is along the CL of the roadway.

As for whether the given radius is for the CL of the road or CL of the inner lane, it all depends on how it is worded. I worked this problem and I believe it says that the radius is for the CL of the innermost lane. If you were given the radius for the CL of the road, they'd have to give you lane widths so you could compute to the inner lane.

I know which problem you are talking about now .... they do give you the CL of travel lane. Not knowing the context of the question had me thinking for a minute.