Farzin Maniei

Graduation Semester and Year




Document Type


Degree Name

Master of Engineering in Civil Engineering


Civil Engineering

First Advisor

Siamak A Ardekani


In highway design, horizontal alignments provide directional transition of roadways. Three categories of horizontal transition curves are simple circular curves, compound circular curves, and spiral circular curves. Compound and spiral curves, as alternatives to a simple circular curve, are often more costly since they are longer in length and require additional right-of-way. These costs differences are amplified at higher design speed. This study presents calculations associated with using a single elliptical arc in lieu of compound or spiral curves in situations where the use of simple circular curves is not prudent due to driver safety and comfort considerations. The study presents an approach to analytically determine the most suitable substitute elliptical curve for a given design speed and intersection angle. Computational algorithms are also provided to stake out the elliptical curve. These include algorithms to determine the best fit elliptical arc with the minimum arc length and minimum right-of-way; and algorithms to compute chord lengths and deflection angles and the associated station numbers for points along the elliptical curve. These algorithms are next applied to an example problem in which elliptical curve results are compared to the equivalent circular curve and spiral-circular curve results. According to this comparison, the elliptical curve not only provides a smoother and safer transition, but also shortens the length of the roadway. However, the right-of-way requirement for the elliptical curve for this specific example is slightly higher than the right-of-way for the equivalent circular and spiral-circular curves. An added advantage of using an elliptical horizontal curve is found to be a smoother transition in cross-section from the normal crown to full superelevation, as this transition can be achieved more gradually through the entire length of the elliptical arc. The transition is likely to be more aesthetically pleasing as well.


Civil and Environmental Engineering | Civil Engineering | Engineering


Degree granted by The University of Texas at Arlington