The job description should say if travel is required for the position and, if so, what percentage of time it would be required. If it doesn't, don't be afraid to ask follow-up questions here to determine the frequency of travel and distance required. Knowing all the details will allow you to answer more honestly. Think about whether you would be able to travel and if you would need advanced notice each time. If you have limitations that restrict your ability, be upfront about it. If you have some flexibility speak openly about the circumstances.