After reading through the datasheets, there are a number of differences between these devices, though I think either would work well in bus stops. Probably the most obvious difference would be the IE 4000 supports higher bandwidths and provides a user friendly GUI Device Manager for simplified management. Below are the links to the datasheets, I would recommend reviewing these and weighing your options based on the functions you wish to implement.
http://www.cisco.com/c/en/us/products/collateral/switches/industrial-ethernet-2000-series-switches/datasheet-c78-730729.html
http://www.cisco.com/c/en/us/products/collateral/switches/industrial-ethernet-4000-series-switches/datasheet-c78-733058.html
