The I-5 narrows down from 12 to 6 lanes after the SR-91 (Riverside and Artesia Freeways), which is a huge bottleneck. Now Orange County is widening (http://www.octa.net/I5Gateway.aspx) it to 10 lanes, but how about the Los Angeles county section? This part also has 6 lanes, and 8 lanes a bit further north, but it's a good idea to widen I-5 to 10 lanes all the way to the I-605 interchange.
Although traffic volumes decreased from 178,000 to 168,000 between 2006 and 2008, an I-5 widening might relieve some pressure on other freeways, such as the SR-91/I-605 route.
Cal Trans has had plans to widen I=5 all the way up to I-710 for years. They are still dealing with the communities involved and the environmental red tape to get the project off and running. The first part of the project, replacing and widening the Carmenita Rd bridge (which is desperatley needed) is supposed to get underway later this year.
Carmenita Road? Wasn't that contract advertised about two years ago?