The District is building a streetcar system while also studying the potential for express bus lanes in key areas. Montgomery County is looking at building a bus rapid transit (BRT) network. Arlington and Fairfax counties are planning a streetcar on Columbia Pike, while a BRT line is under construction in the Crystal City-Potomac Yard area in Arlington and Alexandria.

It’s easy to get confused about the differences between these various transit projects. Moreover, it’s easy for opponents of certain projects to use this confusion to misdirect residents when comparing different types of transit projects.

Two weeks ago, for instance, Arlington County Board member Libby Garvey wrote on this page that she opposes a streetcar on Columbia Pike and instead favors what she calls “modern bus transit.” Unfortunately, nowhere did she define this term, which isn’t a real name for a type of transit. Personally, I favor “Star Trek”-style transporters on Columbia Pike, which would be far faster than any car, bus or train, but those are just as nonexistent.

Garvey brought up examples like Cleveland’s “HealthLine” BRT. The leading Arlington anti-streetcar Web site shows a picture of the Eugene, Ore., BRT as if it were the answer for Columbia Pike. But Cleveland’s and Eugene’s buses run mainly in grassy medians and other special dedicated rights of way. If anyone knows of a grassy median on Columbia Pike, please alert the county staff, because it’s about as visible as the Easter Bunny.

Let’s understand the various types of transit.

You’re almost certainly familiar with the Metro, which is what transit experts call heavy rail. These trains don’t share the roads with cars or trucks. They are fast (when adequately maintained) and have high capacity but are expensive to build.

A somewhat slower but also cheaper approach is light rail, which uses shorter trains that can operate on tracks embedded in regular roads in some places and their own dedicated lines in others. Maryland is planning two light-rail lines, the Purple Line in Montgomery and Prince George’s counties and the Baltimore Red Line. Both will run on both streets and off-street tracks, including through tunnels in some spots.

Streetcars are like light rail, but they usually employ even shorter trains and operate entirely or almost entirely on streets in mixed traffic. This is a good option when there isn’t room — or it’s politically impossible — to set aside a road lane exclusively for transit.

As for buses, you’re almost certainly familiar with regular ones, which run on the same roads as cars and trucks. They start and stop a lot, or if it’s an express line, perhaps not so much. Bus rapid transit is a mode that seeks to duplicate many characteristics of light rail, such as running in dedicated lanes at higher speeds, with special stations rather than basic bus stops.

If a jurisdiction is designing BRT, it’s very important to make sure the project includes dedicated busways and other features. Good BRT lines also let riders pay at stations before they get on the bus, have platforms so riders can board without having to climb steps, configure traffic signals to stay green if a bus is approaching, and more.

Often, especially in the United States, officials start out looking at BRT but gradually shave pieces of the project down, little by little, until you’re just left with a regular bus line that has newer vehicles and fancier paint. This is known as “BRT creep.”

Montgomery County is considering actual BRT with dedicated lanes, and it’s a good idea — as long as officials stick to their guns and really give the buses dedicated lanes and other features of world-class transit systems.

It would be fantastic to dedicate lanes on Columbia Pike, but the Virginia Department of Transportation isn’t willing to consider reallocating space from cars to transit, even if more people would be moved in the higher-capacity trains or buses. That’s too bad, but as long as that’s true, streetcars are Arlington’s best bet.

Even though they run on regular streets, streetcars can transport more people than buses can and usually stimulate more economic development than an equivalent bus project. (Garvey claimed otherwise while comparing rail and bus projects that aren’t even remotely equivalent.)

Because of these advantages, streetcars also make sense on many D.C. streets, such as H Street NE and Georgia Avenue NW. That doesn’t mean the District shouldn’t also create some dedicated bus lanes. Fortunately, Mayor Vincent Gray has included funding for bus projects along with the streetcar in his latest budget.

One mode is not better than another in all cases. On Columbia Pike, though, the streetcar is the right mode; in Montgomery County, BRT is a good approach. The District can benefit from both. But beware claims about “modern buses” or other vague solutions. If someone says you can get of the same benefits of one mode much more cheaply with another, chances are you’ll end up with few or no benefits at all.

David Alpert is editor of the blogs Greater Greater Washington and Greater Greater Education.