Excitebike had one in the 80s!
https://youtu.be/sKef8Axd-io
This would be too much for the base game perhaps, but it would be a fun programming exercise to create a map builder with simple touch controls.
Allow movement only in the 4 predetermined Y coordinates (for changing lanes), and all across the positive X axis (the player starts near the 0 of X always)
UI
Buttons
Left side
Background toggle
Buildings toggle
Song toggle
Right side
4 arrows for moving in all 4 directions (Y axis only goes through 4 predetermined values for lanes)
A create button and an object toggle (cone, coin, 4 differently colored cars) above the arrows.
Top center
General UI
Coordinates
Display a "crosshair" that shows where the pointer is.
The coordinates could be displayed in the bottom left under the toggle buttons.
If the "crosshair" is over an existing obstacle, don't allow creating an object.
#Saving a scene
Create a format for saving all this data neatly in a JSON, load a list of saved names and when a name is selected, the JSON will be parsed and based on that info the objects will be added.
Once the objects are set and added, enable all their required scripts, enable the player/camera movement and the music, and that should be that.