Road network traffic datasets have attracted significant attention in the past decade. For instance, in spatio-temporal databases area, researchers harness road network traffic data to evaluate and validate their research. Collecting real traffic datasets is tedious as it usually takes a significant amount of time and effort. Alternatively, many researchers opt to generate synthetic traffic data using existing traffic generation tools, e.g., Brinkhoff and BerlinMOD. Unfortunately, existing road network traffic generators require significant amount of time and effort to install, configure, and run. Moreover, it is not trivial to generate traffic data in arbitrary spatial regions using existing traffic generators. In this paper, we propose Minnesota Traffic Generator (MNTG); an extensible web-based road network traffic generator that overcomes the hurdles of using existing traffic generators. MNTG does not provide a new way to simulate traffic data. Instead, it serves as a wrapper over existing traffic generators, making them easy to use, configure, and run for any arbitrary spatial road region. To generate traffic data, MNTG users just need to use its user-friendly web interface to specify an arbitrary spatial range on the map, select a traffic generator method, and submit the traffic generation request to the server. MNTG dedicated server will receive and process the submitted traffic generation request, and notify the user via email when finished. MNTG users can then download their generated data and/or visualize it on MNTG map interface. MNTG is extensible in two frontiers: (1) It can be easily extended to support various traffic generators. It is already shipped with the two most common traffic generators, Brinkhoff and BerlinMOD, yet, it also has the interface that can be used to add new traffic generators. (2) It can be easily extended to support various road network sources. It is shipped with U.S. Tiger files and Open Street Map, yet, it also has the interface that can be used to add other sources. MNTG is launched as a web service for public use; a prototype can be accessed via http://mntg.cs.umn.edu.