The Navitia PHP Sample Code by Navitia demonstrates developers how to interact with the API for integrating transportation features. It provides environment, logger, utilities, and tests as available resources.
If you're looking for a traffic data web service, you probably have not been able to find one for free. Now mapping pioneer MapQuest is beta testing a service it says provides "real time traffic information related to incidents, markets and flow."
Five APIs have been added to the ProgrammableWeb directory in categories Currency, Transportation, and Location. Highlights include an API for cannabis data retrieval and an API for locating application users down to the geocoordinates. Here's a rundown of the latest additions.