“Speaking” to the Johnny DC point on the open world map will give you markers for that section of the open world. The resulting finish line flags that dot the map are races that unlock the majority of the vehicles.. After completing each race you will be awarded a new ride. Once all of the flags are checked off you should be missing Lex Luther’s Mech which is only obtainable after reaching 99.99% and located inside the Hall of Doom.
There are Acrobat, Flight, Speedster, and Advanced Glide Races that require characters with those abilities... however you can switch to a flight character to finish all of them. Wonder Woman acts as a Acrobat and a flight character.
There are Bicycle, “Special Vehicle” such as the tractor, Car, Motorcycle and Small Boat races as well.. you can not complete these outside of the assigned vehicle.
Each starting line shows what type of race they are... some can be completed with a combo of different vehicle. Most notably Car or Motorcycle.