Proposed Roadway Profile at Top of Curb

[chluz]

The Client has asked that all street design profiles will need to be based on top of curb elevations, not centerline elevations.

The Proposed roadway will be a 4-lane roadway with a 14-ft raised median with curb&gutter along the median and outside lanes.

I plan to set the profile grade point at the left & right top of curb at the median. I don't know what happes when you lose the median to form a left-turn lane. Does the profile show a vertical drop? In addition, how do I check for design criteria like K values when my profile is along the top of curb? Do I offset the profile down in Geopak to check these values?

 

[gtrainor]

Never seen that before. Obviously a complete road profile should show left & right profiles, but the mechanics of a road profile has to based on the centerline. I think your client needs to stop being the engineer. The elevation change in the left hand turn lane has to be obsorbed in the reduced width median. Typically you go from a 14' median to a 2' median to accomidate a 12' wide left turn lane. The elevation change for a 2% cross slope for the 12' wide turn lane will only be 0.24'. Label your TOC's well to make sure it actually gets built that way. Your local road specs are probably different but I hope you get the idea. Hope this helps. GT

 

[RWF7437]

There is no law that says you may NOT draw multi-line profiles such as; left top of curb, centerline, right top of curb.

You may also draw as many cross sections as necessary to define the roadway.

Your guide should be to answer the question; Can an experienced Contractor build this road based on the information shown on my plans ?

Only if your Client will stamp and sign the plans should he , or she, dictate what they must contain. Besides, some junior engineer at some regulatory agency can probably overrule you both.

good luck

 

[Dozerman56]

Check with whichever municipal department is going to review and approve the plans, they may have standards dictating what they expect to see.

 

[PELS]

I agree with RWF7437.

You can design the roadway like you always do, then profile any aspect of the proposed improvements including crown, centerline, TC, gutter FL, EP, etc.

I have seen this with several municipalities and is not that uncommon around these parts (Northern California), although mostly you see centerline or crown. It's mostly when you have a local jurisdiction (city, county, special district, etc.) as a client that you get these kinds of requests. If you have sweeping horizontal curves, profiling TC on the outer edges of the roadway helps to visualize a superelevation if it is a higher speed roadway.

Bottom line is you don't need to change the way you are use to designing a roadway. You just change what you are normally accustomed to profiling on the plans.

 

[PELS]

One more thing. If you are designing a street with slower design speeds (say <45 MPH) and you are in flat land, profiling the outer TC's helps to spot areas on those horizontal curves where the gutter grade gets flatter than centerline grade and water will collect or move slower. This comes into play when centerline grade is at the minimum allowed by design standard.