Multimodal traffic monitoring is critical for improving the mobility and safety at the intersections with potential conflicts among various modes of transportation. Traditional traffic monitoring approaches utilizing camera cannot work reliably during the night and under hazard weather conditions. We propose to build a new intelligent multimodal traffic monitoring device using the low-cost mmWave radar. The proposed device can reliably distinguish different modes (such as buses, pedestrians, bicyclists, trucks, motorcycles, etc.), and determine the counts, speed, and moving directions of every single target in an urban environment under various lighting and weather conditions. In the study, a low-cost prototype system will also be built and tested for data collection at a major intersection near the University of Arizona. The proposed research can build a foundation for commercializing a new traffic monitoring device through the project.