Changes

Take the bus to Betis. Ask for the direction of the autopista. At the end of the avenida de la raza is a roundabout. Underpass the highway to the second roundabout and get a ride. You can go via the highway or the parallel road, which also works, since a lot of people want to avoid the highway toll. But it's slow of course.

So maybe use a sign "Cadiz";.