Microfluidics has the potential to revolutionize long DNA separation. One of the most promising separation geometries is the microfabricated post array. To increase engineering knowledge of the separation process, we will study DNA transport in this geometry with the purpose of improving DNA size separation. We use a combination of experiments, simulations, and theory to reach a better understanding of DNA transport in these devices. Our improved theoretical model will allow insights into the separation process and allow improved engineering of future devices.