Barranquilla is a town in Colombia.
West towards Cartagena
You can either get a bus (04/2019: COP 2,300) going to Universidad del Norte or Puerto Colombia and get out at Cementerio Jardines del Recuerdo. Almost right next to the cemetery and university campus you will find a Terpel gas station (11°00′55.6″N 74°50′48.47″W) with quite a lot of cars heading straight to Cartagena.
East towards Santa Marta
After the round about at the intersection of calle 17 with carrera 9 there are a multiple gas stations in a row where many trucks and cars stop (10°56′57.82″N 74°46′13.13″W). They all go in the direction of Santa Marta and at least pass by Cienaga after which the road splits towards Santa Marta or down to Santander. The place there is little bit messy but there are many cars and trucks which you could ask and it's easy to find something. Also the bus station for Santa Marta is right there towards the big roundabout in case you don't find anything.