When journalists reach for a word meaning "transit riders" or "constituents of transit" they often seize on the word commuter.
Definitions of to commute (in its transportation sense) vary a bit. Webster says it means "to travel back and forth regularly (as between a suburb and a city)." Some other definitions (e.g. Google) suggest that commuting is specifically about travel to work or (sometimes) school. The core meaning seems to be a trip made repeatedly, day after day.
But in practice, this meaning tends to slip into two other meanings. As with most slippery words, confusion between these meanings can exclude important possibilities from our thinking.
One the one hand, the meaning is often narrowed to "travel back and forth during the peak period or 'rush hour.'" This narrowing arises from the inevitable fact that most people engaged in policy conversations -- especially in government, business, and some academia -- have jobs that lead them to commute at these times. What's more, many people who are happy to be motorists often care about transit only during the peak period, when it might help with the problem of congestion. Reducing the meaning of commute to "rush hour commute" narrows the transportation problem to match these people's experience of it.
Of course, cities, and especially transit systems, are full of people traveling to and from work/school at other times, most obviously in the service sector (retail, restaurants) but also in complex lives that mix work, school, and other commitments. But these trips, even if made regularly, are quietly and subconsciously excluded from the category of commutes, when the term is used to mean only "rush hour commuter."
There's nothing wrong with talking about rush hour commute trips, of course. They're an important category that must be discussed, but I am always careful to call them peak commutes. The problem arises when commute can mean either the narrow category of peak trips or the larger category of all regularly repeated travel. That's the essence of a slippery word, and the danger is higher because this slip is exclusionary. When the word is used in a sense that is narrower than its definition, large numbers of people are being unconsciously excluded from the category it defines, and thus from our thinking about that category.
The word commute can also slip in the other direction, becoming broader than its literal meaning. It's common to see the word commute used as a one-word marker meaning "movement within cities." The excellent Atlantic Cities website, for example, uses "Commute" as the name of its section on urban movement in general. This, presumably, is also what the New York Times means when it refers to San Francisco's BART system as a "commuter train." BART runs frequently all day, all evening, and all weekend, serving many purposes other than the journey to work or school, so its effect on urban life is much broader than just its commuting role. When a word's meaning slips to a broader one, it can falsely signal that the broad category is actually no bigger than the narrow one -- in this case that all urban travel is just regular trips to work or school. This takes our eye off the remarkable diversity of urban travel demands, and the much more complex ways that movement is imbedded in all aspects of urban life.
So commute -- and the category word commuter -- refers technically to a regularly repeated trip, usually for work or school. But in journalism, and in the public conversation, it's constantly being either broadened to mean urban movement in general, or narrowed to mean "rush-hour commuter."
What can you do? Be careful. When you mean "regularly repeated trips," say commutes. When you mean "regularly repeated trips at rush hour", say peak commutes or rush hour commutes. When you mean "all travel at rush hour, regardless of purpose or regularity," say the peak or rush hour. When you mean "all urban mobility or access," speak of urban access or mobility.
Any linguist will tell you that the slippage in word meanings -- especially their tendency to slide to broader meanings or narrower ones -- is a normal feature of the evolution of language. I have no illusions that this process can be stopped. But when we're having public conversations, slippery word usages are the most common way that strong claims to hegemony or exclusion can hide inside reasonable-sounding statements -- often hiding even from the person speaking them. Learn to recognize slippery words (see my category Words, Unhelpful) and look for them, especially in journalism.
Yet another reason, by the way, to hire literature students!