Traffic Cam apps are pretty popular. Traffic Cam Viewer (free for a limited time) is basic but does the job, and it works for traffic cameras just about anywhere in the world. Most of the traffic apps are specific to a region or particular road, while Traffic Cam Viewer can be set to view cameras almost anywhere.
To get things started, you take a trip to the setup menu and scroll to an area you are interested in. It could be a state in the US or another country altogether. Another scroll wheel then appears, from which you can select specific traffic camera locations. In preferences, you can adjust the display for the number of viewable columns.
Traffic Cam Viewer for iOS
Traffic Cam Viewer can go beyond the basics of just looking at traffic camera feeds, which sets it a bit apart as an app of this genre. If you click on a specific camera the image zooms in, and that feed can then be shared with others. The traffic appears to update in real time, with a new frame appearing every few seconds. Frame rate is dependent on what the particular camera is sending. In my area some of the cameras were not functioning, and Traffic Cam Viewer warned me when I selected them.
The app is ad-supported, and I didn't find the ads intrusive, especially since the app is free for now. I doubt if I'd want to see the ads if I was paying for the app.
Traffic Cam Viewer requires iOS 4.3 or greater. It's a universal app and it's optimized for the iPhone 5.