Because of being an .obj import, the text isn't really text - just lines which happen to be text shaped. They are not "editable" in the sense of being able to just type in new text.
Create Panel > Shapes (tab) > Text
Font Arial Bold, Size 186, Kerning 7
Add an Extrude Modifier, align the text (in Y) to the existing text object.
Notes.
Size may be different - the whole thing imported rather large on my system. The thing is to make the new text the same size as the original - trial and error is the easiest way
😉I wouldn't use the attached scene as a basis for any further modifications as the scene scale will undoubtedly be wrong.
Also, the spacing between the words doesn't quite match the original. You may be better off creating each word separately.
freewaysign.zip
Max 2016 (SP1/EXT1)
Win7Pro x64 (SP1). i5-3570K @ 4.4GHz, 8Gb Ram, DX11.
nVidia GTX760 (2GB) (Driver 430.86).