There are several types of radios available for use in the US that are license free. You could choose CB, FRS, MURS or 900MHz business radios.
For a road trip between vehicles, here are some considerations.
The 900 MHz radios are intended primarily for business use but can be used by anyone. They can be pricey for general consumer use on a road trip, and they are limited to 1 watt, but they offer great coverage, largely due to their higher frequency range.
FRS radios are a common choice, but they are limited to 2 watts and are not allowed to have removable antennas, which means your range will be reduced when using them inside the vehicles, because the antennas are completely surrounded by metal and glass.
MURS radios are also limited to 2 watts, but they are allowed to have removable antennas, which means you can mount external antennas on each vehicle which will greatly extend your range, much more than a few extra watts of power. These radios can also be used by either businesses or consumers.
Then there are CB radios. These are commonly used by commercial and many recreational vehicles on the road. They have a legal limit of 4 watts, but there are many options available for external antennas that can maximize range on the road. Add the emergency channels that can be handy for roadside assistance, it is a logical choice for many on road trips.