We developed a web application demo, dynamically monitoring and visualizing the traffic condition in New York City, with a focus on Manhattan. We took advantage of two public API providers: Tomtom and Openweather, for traffic-related streaming data including real-time intersection speed, historical density, and weather details. We proposed a novel congestion model and updated the traffic heatmap every 15 minutes. We implemented our visualization by Google Maps APIs and similar to Google Map layout, we quantified the congestion into three degrees and plotted streets with colors. Our demo achieved similar performance with Google Maps, but with more reasonable and accurate results. Our work can also accept streaming data to achieve high-level concurrency.