Travel is totally fine in the 4th month as long as your route isn't too bumpy. I used to carry a small cushion for back support and always kept a water bottle and dry snacks handy in my bag. Just avoid rush hours if u take public transport to save energy.
I'm in my 5th month now and still going to office thrice a week! Actually, some days are super tiring. Are you planning to use cabs or public transport? I find that taking regular breaks to stretch helps a lot.
Look, the second trimester is generally the safest time to travel. Just make sure u aren't standing for long or riding on extremely bad, potholed roads. If you're driving or going by cab, wear your seatbelt under your bump and take it easy.
Please be very careful and check with your gynac first. I had some spotting in my second trimester, and my doctor immediately put me on travel restriction. Everyone's body is different, so get a green signal from your doc before you start daily commuting.
This is a great question, even I was wondering about this for when my time comes! How do you handle the morning sickness while commuting? Hope your office is accommodating with flexible hours.