If you can turn your roadway data into a linear reference system based on miles, you could then add the crash data as events along the routes. You mention your 'Roadway shapefile having MilePost/Markers in the attribute table'. What do they look like? How are they stored? In whole numbers or decimal?
Thanks for the note. The Roadway data didn't have mile posts, but I created one using the split tool at 0.1 mile distance and then converted them to point file (centroid tool for lines to points) which then had the mile post kind of data. Now the crash data mile posts are in 2 decimal places. So, I am trying to match them with the data set I created and do a join or something. Let me know if there is a better way to get the lat-long data from a set of mile posts on a know roadway when I have the TIGER shapefiles for US/ State roadways. Thank you.
I think you're on the right track. With a little tinkering you should be able to create a locator that can match your crash 'address' to the 'address' of a mile post. If you want to match at 100% I suggest you round your crash data up or down to one decimal.
Commonly used address locator styles—Help | ArcGIS Desktop (Specifically the single field type)
Were you able to get the GPS coordinates this way? I have shape file with linear reference to the routes. I created the route in ArcMap and then successfully plotted the events on my created route. I am not sure how to go on from there to get the GPS coordinates for each event. I appreciate your help.