In case you haven't figured it out already, I'm a huge politics nerd. That's why I do things like listen to Whittier City Council meetings. One issue that currently vexes some folks in my home city is spillover parking at trailheads. For example, the Hellman Park trailhead at the north end of Greenleaf Avenue just north of Orange Drive has a small parking lot that is routinely overwhelmed. Motorists looking to hike park on the streets, which angers the people who live on those streets, who complain to the City, which makes preferential parking districts (PPDs) for residents only, which causes the hikers to park on the streets a little farther out, which causes those neighbors to complain to the City, which causes a new preferential parking district to be created, etc., ad infinitum. I've always thought the PPDs were funny, since hikers, by definition, are people who don't mind walking a bit farther.
The current system doesn't really make anyone happy. Hikers have to park farther away and residents have to buy parking permits. Expanding the parking lot at the trailhead would cost the City money it doesn't have and would pave over valuable nature, plus the site is constrained by water storage infrastructure that probably can't be moved except at an extraordinarily high cost.
There are two realistic things Whittier could do at this trailhead that it is not currently doing.
First, it could install some bike racks. Currently the Hellman trailhead has no bike parking at all (at least that I can recall). Bike parking takes up much less space than car parking, so you could accommodate a lot of cyclists on a small amount of land. It's also cheap, especially compared to the cost of expanding a parking lot. The surrounding streets aren't too bad to bike on, and the site is reasonably close to the Whittier Greenway Trail, a major bike path, not to mention bike lanes on nearby portions of Broadway and Greenleaf.
The second, more effective, and more controversial thing would be to open up the parking permits to anyone, not just residents. This would allow hikers to purchase parking permits. This would make money for the City, which it could use to fund improvements in the neighborhood (perhaps culminating in a parking structure for the trailhead or a weekend shuttle to the parking in Uptown). My philosophy is that public streets should be open to the public. Adjacent property owners may think they own the parking in front of their houses, but they really don't. It's in the public right of way. Hellman Park is a regional asset that provides important access to nature in the middle of Greater Los Angeles. It certainly shouldn't be treated as the private property of the people who live immediately around it. However, local politicians have strong incentives to please their constituents. The residents are potential voters, whereas the hikers may not even live in the City, and hence, have much less political clout.
Tip for people coming in: you can always park in the garage at 6711 Bright Avenue in Uptown and walk to the trailhead. This adds 2.5 km (round trip) to your hike. The parking is cheap and you can stop for lunch in the heart of Whittier! Also, the Montebello 10 Bus and Metro 270 Bus are options you can consider.