Travel handheld baggage?

Depends on the airline and carrier. Different planes have different allowances although there seems to be a standard, you can check with your airline online.

My usual standard-sized carry-on was considered too big for one flight and they had to check it in.
 
I think you're safe with the 55. I recently flew to Canada and took the Via Rail train while there. The train also has carry on rules. I measured everything and followed the rules so carefully, but I was surprised to see plenty of people with bags over the limit carrying them on. If you stay within each carrier's measurements, you should have no problem.