People tend to compare "entire road network" to "one limited transit line" when thinking about ridership. The capacity of one highway lane with just the perfect amount of traffic (meaning full capacity but not congested overcapacity) is optimistically 24,000 40,000 per day. Of course that's not how highways work in practice. At peak times they're congested, and at off peak times they're undercapacity. 48,000 daily ridership is a lot.