The design of WDM optical networks is an issue for telecom operators since the spreading of this technology will not occur unless enough performance guarantees are provided. Motivated by the quest for efficient algorithms for the Routing and Wavelength Assignment problem (RWA), we address approximations of the fractional multicommodity flow problem which is the central part of a complex randomized rounding algorithm for the integral problem. Through the use of dynamic shortest path computations and other combinatorial approaches, we improve on the best known algorithm. We also provide directions for further improvements.