I’ve been an adjunct university professor for 12 years. My students knew they had to be darn good to earn an A.

If a student earned 90 percent as a final grade in one of my classes, I’d give them a high-five.

So L.A.County Metro should be happy with the results of its latest customer survey conducted in September-October 2017, in which the transit agency received 14,400 completed surveys. Surprisingly, 90 percent of bus riders were satisfied with the service, as compared to 88 percent of rail passengers. It’s the second year in a row when bus rider satisfaction topped rail riders, and only the second time since 2003.

Wait. Say that again? Bus riders were more satisfied than rail passengers? A head-scratcher, considering the many complaints heard at board meetings of buses not running on time and carrying suspicious characters.

One theory says recent train riders on new or extended lines (Gold, Expo) may be nonplussed by the experience. Since 39 percent have a car (as compared to 17 percent of bus riders), they might still have fond memories of driving alone in leather seats listening to their favorite podcast, compared to pushing into a sea of humanity for a seat on a train full of strangers.

The issue of personal space lies at the center of a mass transit experience: you have little. Which brings me to the number of people who reported being sexual harassed at least once on a Metro rail train. It rose from 18 percent to 21 percent — or one in five.

Incidents of physical touching, such as groping, were much lower, 5 percent, and down from 7 percent in 2015; reports of someone exposing themselves rose by a percentage point to 9 percent.

Bus riders taking the survey reported fewer incidents in almost all categories (except for groping which tied train riders at 5 percent). Maybe the ergonomics play a role. Bus seats are more compartmentalized than rail seats. Most riders on a bus face forward so they’re looking at the backs of heads. On a light-rail train, seating is more, um, intimate, or can be. There’s more standing, more bumping up against legs, arms, bodies in general. And some trains (Red Line, Purple Line) are underground, unlike buses.

Also, more bus riders are female at 55 percent; female rail riders make up 46 percent of the total. Usually it’s males doing the harassing and there are more men riding trains than buses on Metro.

Ninety percent said they feel safe riding the bus. Only 79 percent of Metro train riders said so. To report sexual harassment, Metro added a hotline last year: 844-633-5464 and increased the number of police and Metro security.

Moving on to other results, here’s one I don’t find terribly shocking: Smartphone usage is way up for train passengers (94 percent carry some type of cell phone) and 91 percent for bus riders. That leaves room for innovative ride services via phone apps. Or using phones for alerting passengers to schedules, delays and service cancellations.

What’s always startling are the differences in median household income between Metro bus and rail riders.

Bus riders have a median income of $16,218 and 61 percent are below the poverty line. Metro rail riders’ median household income is $24,390 with 39 percent below the poverty line. The only way that could balance out is when Metro builds more light-rail lines servicing lower-income neighborhoods. Completion of the Crenshaw Line — about 18 months away — may help.

Obviously, Metro is trying to lure the middle class onto trains. Hence new lines into Santa Monica and the burbs of the East San Gabriel Valley. How they spend $6.1 billion next year is up for debate. Bus routes may be changing as well. To give your opinion on the Metro budget and its “NextGen” bus restructure study, join a telephone town hall on Wed., April 4 and Thurs., April 5 from 6:30 p.m. to 7:30 p.m. by dialing 888-400-1932.

Steve Scauzillo covers transportation and the environment for the Southern California News Group. He’s a recipient of the Aldo Leopold Award for Distinguished Editorial Writing from The Wilderness Society. Follow him on Twitter or Instagram @stevscaz or email him at sscauzillo@scng.com.