MAX Yellow Line is a north-south Light Rail line linking Downtown Portland to North Portland ending at the Expo Center. The line opened in May of 2004. Originally it joined the Blue/Red Lines at the Steel Bridge and ended at the 11th avenue MAX turn-around. It was later shifted in 2009 to the Transit Mall and 5th/6th avenues terminating at PSU. Finally in 2015, most Yellow Line trains are through-routed with Orange Line trains to Milwaukie.
Most of the Yellow Line is in the median of Interstate Avenue through North Portland. There has been a lot of talk to extend the line into Vancouver. But Clark County, (Washington) has turned done all proposals to extend MAX to Vancouver. The death blow to the proposal was Washington State pulling out the of the planned replacement of the Interstate Bridge. Oregon decided they could not build a bridge on their own, so the Columbia River Crossing project was killed along with the light Rail component of the project. I find this sad
The cache is nothing special, but does afford a view of the Yellow Line, as well as the Fremont Bridge.