Reverse Curves 2

[CivilTyro]

Does anyone help me in finding minimum tangent lenghts between reverse curves for rural/local urban strrets? Does AASHTO green book has any info on this? Thanks for the help.

 

[civilperson]

Think about the PRC in your reverse curve, does it have a tangent length at that station? The answer is the same as connected reverse curves!

 

[ACtrafficengr]

What is the superelevation for the two curves? What is the runoff length?

"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

"I'm searching for the questions, so my answers will make sense." - Stephen Brust

 

[CivilTyro]

Thanks for the posts guys. I could not find any useful info in AASHTO. Google is not much of help either.

 

[PELS]

Check with the local design standards of the jurisdiction where the road design will be reviewed or with the standards of nearby cities or counties. They ususally spell out the minimum length of tangent between reverse curves. Sometimes it has to do with the design speed and the topography as well as analysis of safety issues. Some cities will allow a reverse curve without a tangent in between. In California, Caltrans (California Dept of Transportation) design standards are usually the default standards of the cities.

 

[civilman72]

To answer your question simply, there are no set minimum tangent length requirements.

AASHTO does not have any minimum tangent lengths, only minimum lengths of runoff/runout for roads that are superelevated; these runoff/runout distances are generally then considered minimum tangent lengths.

If your road is superelevated, you minimum tangent lengths are driven by the runout/runoff lengths, and a few other design parameters.

If your road is not superelevated, then minimum tangent lengths should be included in your local review agency road design standards - some do not require any at all.

As a designer for numerous low-volume roads, I am usually OK with designing reverse curves with no tangent length, but I do use minimum tangent lengths when designing compound curves ("broken-back") with largely differing radii.

If your new to road design, read Pgs. 229-230 of the PGDHS (2004)(updated "AASHTO Green Book") for some very useful discussion about horizontal road design issues.