The Surface Autonomous Bus Network—officially the Meridian Public Surface Transit System, universally called the MAST or simply the bus—is the largest by ridership of all transit systems in GLMZ, carrying an estimated 2.1 million passenger trips daily across 847 active routes covering all districts including peripheral and unzoned areas. MAST vehicles are electric autonomous platforms, typically 40 to 60 passengers in standard configuration, operating on fixed routes with dynamic schedule adjustment based on real-time demand data. Unlike the Spine or SkyReach, MAST operates without hard access tiering—any individual capable of paying the flat 4-credit fare or presenting a subsidized transit credential can board any route, a feature that makes it the only major transit system in the city accessible to the full socioeconomic range of the population.

The autonomous operation of MAST vehicles uses a sensor suite broadly similar to the freight crawler platform—LiDAR, radar, and visual systems with V2X infrastructure communication—but calibrated for mixed-traffic urban environments where pedestrian interaction density is far higher than in dedicated logistics corridors. MAST vehicles operate under a conservative autonomy protocol that prioritizes collision avoidance over schedule adherence, with the practical consequence that routes through high-pedestrian-density areas often run significantly behind published schedules. The MTA's own performance data shows on-time arrival rates averaging 61 percent system-wide, dropping to 43 percent in Districts 6 through 9 and to 28 percent in peripheral area routes, where road surface conditions, informal market encroachments on bus lanes, and higher rates of infrastructure sensor failure compound the baseline challenges.

Funding for MAST comes from a combination of fare revenue, a municipal transit allocation from the city government budget, and corporate district improvement assessments levied on commercial property owners in served areas. The funding formula has been a persistent source of political conflict: corporate interests in upper districts advocate for assessment rate reductions on the basis that their employees primarily use private or premium transit, while lower-district and peripheral community advocates argue that chronic underfunding of MAST is a direct cause of the service quality gap that makes lower-tier transit appear less desirable than it could be. Independent analyses of the funding model generally support the latter position, finding that per-rider infrastructure investment in MAST is approximately one-seventh of the per-rider investment in the Spine.

Despite its service quality challenges, MAST functions as the connective tissue of GLMZ's informal and peripheral economies. Routes that extend into unzoned areas carry workers to employment nodes in mid-tier districts, informal market operators moving inventory, and people navigating the city's social services infrastructure. MAST vehicles have consequently become social spaces with a density and diversity absent from the rest of the transit system—a fact reflected in the disproportionate attention MAST interiors receive from the city's surveillance infrastructure, with onboard camera systems, acoustic monitoring arrays, and automated fare evasion detection all standard equipment on current-generation vehicles. Civil society organizations have documented the use of MAST surveillance data in law enforcement investigations at rates substantially higher than equivalent surveillance on premium transit systems, a disparity they attribute to the socioeconomic profile of the ridership rather than any differential in recorded incident rates.