Blair,
ArcGIS Online routing service uses different network dataset than Google Maps, i.e. this is about different impedance values on particular network elements. Unfortunately, this is hard for me to say which one is more accurate in this particular case since I do not live in that area.
Network Dataset hosted on ArcGIS Online is provided by Tele Atlas and updated regularly. Google uses its own network based on public TIGER data.
Regards,
Dmitry