You are presently working as Junior Engineer (JE) in the State Irrigation Department. Quite naturally your work requires lots of field visit. As far as I know, the next promotion would be as AEN or AE (Assistant Engineer). Once you get your promotion, the filed visit will be much less. But I don't know, when will you get your next promotion and the promotional prospects in your Department.
As this is a State Government job, it is quite natural that in Central Government job, the pay-structure and facilities will be much more at same/similar level. On the other hand, you are presently working in your home-state and you will always work in your home-state (under normal circumstances). But in the Central Government service, there is no surety that you would always get posting in your home-state.
Due to a very good pay structure and comparatively better promotional avenues, SSC-CGL has become very lucrative. The competition is very tough. The topmost successful candidates get the posting as ASO. Fewer successful candidates get posting as ASO in the Railway Board in New Delhi(and remember, not as per your choice in Zonal Railways). You can't be sure that you will get the chance of being selected as ASO in Railway Board.
Considering the above factors, please take the decision and start preparation for SSC-CGL. But it is also pertinent to state that many positions (which are filled on the basis of SSC-CGL) are transferable in nature even in smaller cities and require frequent field visits.
"If you are killed in action, you go to Heaven. If you win, you rule this Earth (as beautiful as Heaven). That is why, O son of Kunti, take a firm resolve and fight!"-- Shrimad Bhagwad Gita