Nowadays the optical atomic clocks that can be used in vehicles are many orders of magnitude less accurate than those that are restricted to a well protected laboratory environment.

If anyone is wondering, we aren't yet to the point of having an atomic clock in the dashboard of your Toyota. But they have been reduced to ~suitcase size. Example if one being tested in a Navy ship:

https://www.geoconnexion.com/in-depth/scientists-create-new-...

https://www.microchip.com/en-us/products/clock-and-timing/co...