The COVID-19 pandemic led to widespread reductions in mobility and induced observable changes in the atmosphere. Recent work has employed novel mobility datasets as a proxy for trace gas emissions from traffic, yet there has been little work evaluating these emission numbers. Here, we systematically compare these mobility datasets to traffic data from local governments in seven diverse urban and rural regions to characterize the magnitude of errors in emissions that result from using the mobility data. We observe differences in excess of 60% between these mobility datasets and local traffic data, which result in large errors in emission estimates. We could not find a general functional relationship between mobility data and traffic flow over all regions. Future work should be cautious when using these mobility metrics for emission estimates. Further, we use the local government data to identify emission reductions from traffic in the range of 7-22% in 2020 compared to 2019.