you would be surprised about the required HP to maintain a steady 70mph on freeway (no acceleration).
If the wind is not against you and you are not uphill, it can be as low as about 20 HP (I have a friend with a BMW that displays in realtime the HP used, this is where I get those numbers).
Knowing that hybrid version of Kia Niro has a 43HP electrical motor, on ideal condition YES it can handle the constant speed on freeway
it is not going to be for a long time but if you are light on the pedal or on cruise control, it happens.
The main reason is that the Niro is very energy harvesting oriented. Which means that when you are on the highway running on ICE, if not all the power of the ICE is used for traction, the remaining HP are used to generate some electricity. After a while, to keep the EV battery to a constant level, the car is going to reuse temporary this stored energy. This is what I really like in this car, nothing is lost
I discovered that on my Plugin (I know, the plugin has bigger battery and the motor is 60HP instead of 43HP, but the principle is still the same).
When I'm on freeway in HEV mode, on a long flat cruise controlled freeway, I can see that the ICE is providing energy to the wheels AND battery.
Then after a while, I can see the ICE turning OFF and battery keeping the constant motion for a little while. It is like a cycle charge / discharge to use the excess of energy. The ratio is pretty low, I would say 1/10 (1 mile free for 10 miles ICE) but still appreciated.
Of course this increases our mpg. For example, my last 2 trips with about 250 miles (way above the 24 EV capacity) I did around 60mpg.
On the opposite, if I drive on a windy road where constant speed is difficult to keep, my mpg can go as low as 47 mpg, which confirms the 47mpg given for ICE only.