ASP.NET MVC Custom Error Handling Application_Error Global.asax?

I have some basic code to determine errors in my MVC application. Currently in my project I have a controller called Error with action methods HTTPError404(), HTTPError500(), and General(). They all accept a string parameter error. Using or modifying the code below.
What is the best/proper way to pass the data to the Error controller for processing? I would like to have a solution as robust as possible.