How Does A Road Marking Machine Work ?

To paint direction arrows, they start with a design which in Spain must be approved by the Road Authority, the paint team has a set of masks (arrows, letters, text), they define the position relative with a measuring tape, they put the mask at the correct position, they spray thermoplastic paint, and then they throw (by hand) over it a handful of plastic reflective pellets while the paint is wet. In this case not even a 10% of the pellets is fixed to the paint.
These pellets are 1mm (or a little more) diameter, and their aim is to reflect light, and also to protrude over the water film when it is raining so the road mark is seen better.
Central marking is done with a road marking machine.
The road marker team starts by painting dots every 10 or so meters (30 feet) at the center of the road. They measure it again with a measuring tape. On straight roads they may even mark a straight line with a rope with cray dust on it.
Then the road marking machine runs at constant speed while it follows the center dots. The front pole of the machine follows the dots, and steers the machine when the road winds.
The machine sprays a thermoplastic paint in a continuous mode for continuous line and with start and stop in case of discontinuous. Timing of the spray going on or off determines the length of the line, being shorter at the end.
In this case a nozzle sprays the paint, and another drops the pellets, as in this diagram--