Adapt to your area. Ride on the Santa Ana River Trail (runs through/near Corona, you might already be doing this) and, as others above mention, choose a different route with wider roads, roads with shoulders, and/or lower traffic volume. I've got the same issues in coastal Orange County, so use the SART quite a bit on weekends. On weekends I'll also ride roads at dawn to avoid the traffic build-up that occurs later in the morning, and during the week I do some pre-dawn loops on local streets near my home ( streets that are busy at 8AM are almost devoid of vehicles at 4:30AM).