The the engine RPM's go up as your speed goes up. That is the way it is supposed to be.
The RPM goes up but the car doesn't pick up any speed.
What kind of transmission? If it is a manual then your clutch may be shot. If it is an automatic then check your transmission fluid level. If the fluid level is good then your trans may be shot. A newer car like yours is probably still under warranty so I would take it to your dealer.
ChelseaDavis-- do you have dual clutch or CVT transmission? I imagine that don't have a manual transmission or do you?
Looking for a Used Elantra in your area?
CarGurus has 2,724 nationwide Elantra listings starting at $659.
Search Hyundai Elantra Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Hyundai Elantra Experts