The areas being connected by the 405 (West LA & San Fernando Valley) are geographically quite challenging for transportation planners due to the Santa Monica Mo

The areas being connected by the 405 (West LA & San Fernando Valley) are geographically quite challenging for transportation planners due to the Santa Monica Mountains. LA Metro plans to build a tunnel through the mountains but it's estimated to cost $20B: https://en.wikipedia.org/wiki/Sepulveda_Pass_Transit_Corridor https://en.wikipedia.org/wiki/Sepulveda_Pass_Transit_Corrido...