Superelevated reverse curve?

[joelrob]

I've been asked by the head engineer of the company to lay out a design for a superelevated, reverse curve with no tangent section between curves. I think it's impossible, as the superelevated curve must remain superelevated throughout the entire curve, right? For the speed to remain constant through the curve, it cannot flatten until the tangent section, but for a reverse curve with no tangent section it's not possible.
Or am I wrong?

 

[BigH]

I'll check with my highway engineer on my project and get back to you. Best regards.

 

[KRSServices]

Just so we are on the same page, what are you referencing by the term "reverse curve"? Are you referring to a vertical curve (sag or crest)? The superelevation is a function of the curve radius, design speed and vertical geometry. The superelevation transitions from the BC to the EC, again, depending on radius and speed. KRS Services

http://www.krs-services.com

 

[wolfhnd]

Your right you cannot follow the rules and do this. That said I have done exactly what you have been asked to do several times over the years on low speed roads and gotten away with it. You should however be allowed to add the tangent based on your judgement. No one should ask you to do this. I work for a govement agency and had no personal liability. Just for the record the designs I did are now close to 40 years old and no law suits have been issued, lucky maybe but probally just a function of the fact that a vehicle does not have time to go out of control before it enters the second superelevated section. If you must do this then make sure to add what ever widening is called for in the tables you are using. Stripe the pavement so the widening is on the wrong side (the high side for curves to the right and the low side for curves to the left).

 

[bridgeboy]

This can be done--and is done every day. What State are you in (geographically, not mentally)? The juristdiction usually has a maximum rate of change for superevevation. On Caltrans work the max. change is 6% per station.

Don't forget to watch the drainage with this concept. Often there can be a nasty side-effect.

Are you using a superelevation diagram? If not, do so.

 

[earle]

AASHTO calls for 60% of the superelevation to be acheived at the PC or PT, thus by implication typically 40% of the super transition is within the curve. Thus super transitions for reverse curves are different only by amount acheived at that point.

I would use minimum transition length, and place the transition through flat at the point of reverse curvature.