Getting Real-Time Traffic Data From Sigalert
Sigalert.com is one of those older sites that still works better than most of the newer alternatives when you need actual incident reports. The interface looks like it hasn't changed since 2003. That doesn't mean it's broken. It means the people who built it focused on the data layer instead of the marketing layer. I use this for commute planning around Los Angeles. The coverage in Southern California is better than anything I've found from the DOT feeds or the Google Maps incident layer. The alerts come from Caltrans sensors and CHP dispatch. You can see them before they show up on the radio or in the app notifications on your phone.
The Ultimate Guide To Sigalert Com Your Onestop Shop For Traffic And Road Conditions
The core value here is the incident map. When you load the page, you get a color-coded map of the metro area. Red means stopped traffic. Orange means slow movement. Yellow is a warning. Green is free flow. Clicking on a segment shows the specific alert text, the time it was reported, and whether it's been cleared. My usual workflow is simple. I open the page about twenty minutes before I need to leave. I check the orange and red segments on my route. If I see a big incident holding up the 405 near Sepulveda, I divert. Most days this saves me twelve to eighteen minutes. On bad days with multiple incidents, it's closer to thirty minutes of avoidance. One thing people miss is the filter options. The default view shows everything. If you're only interested in highway incidents and not surface street accidents, you can toggle those layers off. The site has checkboxes for freeway, arterial, and local road alerts. Turn off what you don't need and the map becomes readable instead of a noise field.
There's also a text list view if you prefer reading over looking at a map. Each alert includes the direction, the nearest cross street or mile marker, the type of incident, and the estimated delay. I've found the delay estimates to be roughly accurate within a five-minute margin. They're not always precise, but they're in the right ballpark for making a decision. Here's something most users don't know. Sigalert data can be accessed via their RSS feeds. There's an endpoint for individual corridors. If you run a script or use a tool like NetNewsWire, you can pull alerts for just the I-10 or the 101 without checking the full site. This is useful if you commute the same route every day and only care about one corridor. I set up an automated alert for the 5 through Van Nuys back in 2019. It runs every five minutes and sends me a push notification if there's a new incident report. The limitation is that the feed format is plain text XML, not JSON. Modern tools expect structured data. If you're building something custom, you'll need to parse the XML yourself. It works fine with Python's built-in xml module, but it adds friction compared to APIs that return clean objects. Caltrans has their own open data portal now, but the Sigalert layer is still more current for active incidents.
Get the Full Details
Another thing to understand is what Sigalert doesn't cover. They don't show real-time speed data the way Waze does. They don't predict congestion two hours out. They report incidents after they happen. If you're looking for predictive analytics, you need a different tool. Sigalert is reactive. It tells you what's happening now, not what might happen later. The mobile version exists but it's clunky. The responsive design is barely there. I usually just use the desktop site on my phone and zoom in when needed. It loads faster than the app most of the time, which is ironic for an older site. The server response is quick, maybe because the page is mostly static content with minimal JavaScript. I ran into a specific edge case last winter. There was a multi-vehicle pileup on the 405 south near the 101 interchange. The main map showed red, but the alert text didn't mention the lane count or the expected closure duration. I had to dig into the individual segment details and cross-reference with CHP's Twitter feed to get the full picture. This happens occasionally. The incident descriptions are sometimes terse. They list the location and the general problem but not the operational details you might need.
The workaround I use is to keep the CHP Los Angeles County Twitter feed open in another tab. When Sigalert shows an incident, I check Twitter for photos and more specific lane information. CHP posts updates faster than they always update the Sigalert system. The lag between a real crash and the database entry can be ten to fifteen minutes during busy periods. For the basics, just go to sigalert.com. No login required. No subscription. The whole thing is free and funded by Caltrans and regional transportation agencies. If you need current incident reports for Southern California freeways, this is still one of the most reliable sources available. The data goes back years if you're doing historical analysis. I once pulled six months of incident reports for a site selection project. The export function is limited, but you can screenshot and compile what you need manually.
