Even highways aren't level. The system will still be able to use the hybrid tech to add a little power here and recover a little power there, so its highway mileage is still usually better than the non-hybrid. Getting those great numbers mean doing a little more than just buying the car. You have to take personal responsibility and drive for mileage. No speeding, no fast starts, and, if possible, take the slower routes. The highlander both hybrid and non, get their best gas mileage around 45 to 50 miles per hour. If you can stay on roads where it is safe to do that, then go for it. Those came road often come into 30mph town where the electric only mode can come into play and boost your numbers even further. It is quite possible to get 27 to 30 miles per hour without using any special techniques other than those I'm describing here. With even more care, planning, and willingness to give a few minutes of your time, you can take those numbers even higher.