Depending on geometric features, closest analogy is to treat like left turn.

Dear Emilio Ochoa,

pl check these link. it may useful for your project.

All the best

http://transportation.ky.gov/Congestion-Toolbox/Documents/NCHRP%20524%20UTurn%20Safety.pdf

https://safety.fhwa.dot.gov/intersection/alter_design/pdf/fhwasa14070_rcut_infoguide.pdf

Un-signalized U-Turn is similar un-signalized right-turn (except the merging direction is different). There are three types: 1. without acceleration lane (lower capacity), 2. with acceleration lane (higher capacity), 3. with a loon or bulb on the opposite side of the road (for large vehicles that cannot be positioned to maneuver like cars). See reference on median U-Turn, and restricted crossing U-Turn.    

I suggest you to review this link, it's in spanish but the information can help to solve your question

https://www.dmv.ca.gov/portal/dmv/detail/pubs/hdbk/driver_handbook_toc/!ut/p/a1/hYxRC8IgAAZ_UXy2KOpRariyURAs54u4uTYxVDbb7496j-7t4DhICEivZ9vrZIPXz4_LjeLHQ74sGOFsfaaE8qK4VHmVsd0Kp3-BQJ2N5b7sIaNOw8L6R4CIr2aCGEzjIMxo525Ug_amCcGpFFrcIb9j8gNKcOsmRCfra9zSN9erbBM!/?1dmy&urile=wcm%3Apath%3A%2Fdmv_content_es%2Fdmv%2Fpubs%2Fhdbk%2Fturns

try SIDRA software

I suggest to read my paper in Researchgate which was published in the ITE Journal. Its title is "Capacity of U-turn at median opening". The paper provides an estimate of capacity based on regression analysis and probablistic approach.