The 260-kilometer corridor between São Luís and Barreirinhas follows the remnants of colonial cattle routes through Maranhão's interior, a journey that once took four days by ox cart and now spans four hours by paved highway. The MA-402 cuts through cashew plantations and low scrubland before entering the transitional zone where the Amazon basin meets the Parnaíba delta, the landscape flattening into the sedimentary plain that birthed the Lençóis dune fields. For travelers bound for Lençóis Maranhenses National Park, Barreirinhas serves as the sole inland gateway, a riverside town of 62,000 where the Preguiças River meets the western edge of the protected area. The road itself carries no intrinsic attractions — no colonial towns, no roadside vistas — but functions as the mandatory transit corridor for every visitor arriving by air through São Luís International. Private transfer São Luís to Barreirinhas services emerged in the mid-2010s as park visitation doubled, displacing the earlier reliance on irregular bus schedules and shared vans with fixed departure windows. Dedicated shuttle operators now maintain fleets of air-conditioned sedans and SUVs, offering door-to-door pickup from São Luís hotels and direct delivery to Barreirinhas accommodations. The route departs the capital's coastal humidity and climbs onto the central plateau, passing through Rosário and Morros before the final descent into the Preguiças basin. Most services include a brief stop in Morros for fuel and restrooms, the halfway mark where the vegetation shifts from dense scrub to sparse caatinga. The transfer functions as prelude rather than destination, the necessary preamble to accessing Lagoa Azul, Lagoa Bonita, and the park's signature white-sand expanses. Shared transfers consolidate passengers into 12-seat vans, departing São Luís twice daily at fixed hours; private options allow flexible scheduling aligned with inbound flight arrivals or early-morning dune tour departures. Return journeys to São Luís typically begin before dawn to accommodate afternoon flight connections, the reverse route offering views of the Preguiças estuary in morning light. The park entrance itself lies 25 kilometers east of Barreirinhas, accessible only by 4x4 or boat, making the town the staging ground for all onward expeditions into the dune interior.