As I remember, Google Directions API allows 2,500 directions requests
per 24 hour period from a single IP address per free user. Does anyone know the limits for Bing Maps and the Routes Rest API (http://msdn.microsoft.com/en-us/library/ff701705.aspx) for free users? I tried to look through the documentation but could not find such details.
Since, nobody has answered, I will answer my own question. You can get a free 90-day Trial Key allows you to evaluate Bing Maps for development of any type of application, including enterprise applications. The Trial Key may be used for up to 10,000 billable transactions within any 30-day span during the evaluation period. http://www.microsoft.com/maps/create-a-bing-maps-key.asp
Any time a Routes API URL request is made to find a route, one transaction is counted. http://msdn.microsoft.com/en-us/library/ff859477.aspx
That means, you can access the Routes API for a total of 10,000 times with a free Trial key.