I have to define what I mean by traffic and transit now so they make sense throughout my writing.
The Webster’s dictionary definition of traffic is a
(1) : the movement (as of vehicles or pedestrians) through an area or along a route
(2) : the vehicles, pedestrians, ships, or planes moving along a route
(3) : congestion of vehicles <stuck in traffic>.
When most people think of traffic, they think of the painful third version of that definition. But I am more interested in the first definition. The Oxford definition (http://oxforddictionaries.com/definition/english/traffic?q=traffic) is even closer to my needs:
noun [mass noun]
(1) vehicles moving on a public highway: a stream of heavy traffic
(2) the movement of ships, trains, aircraft, or pedestrians: Europe’s air traffic
(3) the transportation of goods or passengers: the increased use of railways for goods traffic
None of these definitions define traffic by itself as congestion. Though the first modifier that comes to mind is “heavy traffic”. You need the adverb to make traffic into congestion. “Light Traffic” is not congested at all.
To be specific for the purposes of my writing, I define traffic as “the movement of independently piloted motorized vehicles on a road network, including motorcycles, cars, trucks, SUVs, and tractor trailers”. This is close to but more specific than the first definitions above. The practice of engineering for managing movement on roadways is not called automobile, or vehicle engineering, it is called traffic engineering. They do not call themselves congestion engineers, or car engineers, nor do they call themselves roadway engineers. They deal with the events that happen on the road, and their vehicle of interest has been motorized almost from the start of their profession. They design their signals, markings, lanes and signs for times of heavy and light congestion to balance throughput, access, route conflicts, safety and even other modes like walking and biking. My definition only differs from the traffic reporter definition of traffic. Reporters do not mention traffic unless it is heavy traffic. The absence of disaster is not news.
There are two classes of transit, expensive and cheap. What makes transit expensive are the vehicles, ways and right of way. What makes it cheap is when it reuses the same right of way as traffic. I refer to rail versus bus transit, of course. Using the same right of way as traffic is a difficult bargain for transit, as road networks are set up hierarchically, and transit does best along corridors. The need of transit to stop frequently for passenger boarding and alighting makes it both slower than the traffic around it and slowing to the traffic around it. A bad bargain for all involved. To write about what transit could be, I choose, for the time being, to focus on the expensive stuff: heavy rail, light rail, commuter rail, monorails and streetcars. Streetcars can operate exactly like buses, or they could operate with some dedicated lanes along their routes. It depends on the system. The average cost of building that stuff, including new right of way, rails, power, rolling stock and stations, is about $70 million per mile.
Rail transit, for all the expense, is higher capacity and higher performing than bus transit and traffic. Bus transit is barely better performing than traffic in many cases, an artifact of being mixed with traffic and having much larger vehicles to drive, while stopping and accelerating more than even the other vehicles in traffic. I would like to understand bus transit better, as they are more affordable and call for better design solutions. As they are, however, they are not readily distinct form traffic. So I studied rail transit as transit.
WALKING AND BIKING
As for “walking” and “biking”, both are present continuous verbs, not nouns like transit and traffic. I had no choice. Bikes are just objects unless used by bikers, and walks are routes or routines taken by walkers. As you know, I am developing an allergy to the term “pedestrian”, “pedestrianism” or any other form of pederasty. It sounds more like an affliction than a transportation mode. In the traffic paradigm of the last eighty years, it actually is an affliction. So I use “walking” and “biking” to include the set of people who walk or bike, their vehicles that weigh much less than them, the routes designated or built for them, and the trips taken by walking or biking.
These are the four modes I talk about in my writing.