Wait until leader clears the lunar

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Riding the trolley from West Philadelphia going to University City,


I love the Philly trolleys.  They are clean, fast, and powerful; graffitiless; the drivers are courteous and the riders are polite.  However, since I'm curious about practically everything I encounter, I often wonder how the cars know which of numerous branching tracks they should turn onto, and so forth.  One of the most mysterious things about my daily trolley ride to UPenn is the sign pictured above — somebody else noticed it 7 years ago and was sufficiently amused by the wording to post it on Twitter.

Clearly, this is an instance of occupational argot.  All six of the words of the warning on the sign are common and known to nearly every literate person, but only trolley drivers know their meaning when put together like this.

The miracle of language!


Selected readings



  1. Dick Margulis said,

    April 21, 2022 @ 3:41 pm

    Reminds me of my favorite highway sign in Connecticut: No permitted vehicles allowed.

  2. Philip Taylor said,

    April 21, 2022 @ 3:48 pm

    The sign inspired a poem.

  3. Chas Belov said,

    April 22, 2022 @ 12:22 am

    My favorite highway sign in Connecticut was always the "Road Legally Closed" signs at the entrance ramps for I-84.

  4. Chas Belov said,

    April 22, 2022 @ 12:26 am

    Speaking of transit driver jargon, I've always loved the "Gilley Room," the name for the break room where drivers wait for assignments. I initially thought it was specific to the San Francisco Municipal Railway aka Muni. However, playwright Richard Cartwright set the play "The Gilley Room" in the break room of the predecessor transit company of AC Transit, across the bay in Oakland, so I have no idea what the range of that term might be.

  5. Chas Belov said,

    April 22, 2022 @ 1:22 am

    While I can't speak to "lunar," I'd guess "leader" is industry wide. It's the vehicle in front of you. The precise meaning of "in front" is, I'd guess, context dependent. In the sign in question, it would mean a vehicle which is close in front of you, without regard to whether the vehicle is designate as running on the same route.

    However, I've heard it used here in San Francisco to refer to the preceding vehicle on the route, as in "Where's your leader?" to the driver of a packed bus. How the driver would know that I have no idea, since at the time I heard of this expression we did not yet have the vehicle location devices we have nowadays.

  6. Yuval said,

    April 22, 2022 @ 2:37 am

    So is this nerdview, or do we only use that for signs intended for the public?

  7. Victor Mair said,

    April 22, 2022 @ 7:40 am

    From Kent McKeever:

    What is lunar?


  8. Emily said,

    April 22, 2022 @ 9:35 am

    At last, the perfect solution to the trolley problem!

  9. john burke said,

    April 24, 2022 @ 11:46 am

    Lunar signals–they look white to me, though bluish-white isn't inaccurate–are used by the San Francisco Municipal Railway (Muni) Metro service. It's the fixed-guideway (rail) component of our transit system, much like the subway-surface cars in Philly.

  10. Philip Taylor said,

    April 25, 2022 @ 5:16 am

    I am intrigued by Victor's "I love the Philly trolleys". "Philly" is obviously a reference to Philadelphia, and I assume that "trolleys" is a reference to "trolley-bus[s]es", but is this a common abbreviation in North American ? In the UK, a "trolley" is (most commonly) the thing that one pushes around a supermarket and into which one places one's shopping prior to check-out, but a trolley-bus is always a "trolley-bus" (or "trolley bus", or "trolleybus"), never just a bare "trolley".

  11. john burke said,

    April 25, 2022 @ 9:06 am

    San Francisco Muni also operates trolley-buses, which are powered from an overhead catenary wire but also have diesel engines so they can run on streets lacking the catenary system. As for the name, I grew up in New York in the 1940s when there was still some fixed-guideway surface transit; I learned the terms "trolleycar," "trolley," and "streetcar," but can't remember ever hearing "trolley-bus." I suspect most of these terms are unfamiliar to younger Americans, apart from Philosophy majors.

  12. jaap said,

    April 25, 2022 @ 10:00 am

    To me trolley would mean a trolley-bus (i.e. a road bus that uses overhead electric cables), but in this case it seems to be referring to streetcars or trams, i.e. things that run on rails that are embedded in the road surface or run alongside roads.

    When reading that sign, I would imagine that lunar would refer to the curved part of railtrack in a rail switch, and that the trailing streetcar needs to wait to give the switch time to automatically move if necessary. That sounds plausible to me, but it is pure speculation on my part.

  13. J.W. Brewer said,

    April 25, 2022 @ 6:13 pm

    @Philip Taylor et al.: Philadelphia's varied public transit system still features (perhaps uniquely in North America at present?) both trolleys that run on rails ("trams" in the variety of English you are probably more familiar with) and trolley-buses. But the full text of vhm's post suggests the former, although I can't be bothered ("can't be arsed," I think you say over there) to google up a map of the Philly transit network and see if that makes sense in terms of plausible routes from vhm's house to his office.

  14. Philip Taylor said,

    April 26, 2022 @ 3:21 am

    Thank you, JWB. In fact "can't be arsed" is most definitely not in my idiolect, whereas "can't be bothered" is an integral part, but I have certainly noticed that a not-insignificant minority of my British peers have adopted "can't be arsed", although adopted from whence I have no idea. And yes, "tram" is an inherently meaningful term to me, and I still recall travelling on the last London tram as a child.

  15. Chas Belov said,

    April 26, 2022 @ 7:04 pm

    This transplanted San Franciscan used "trolley" for "tram" when I lived in Pittsburgh (which only had streetcars and diesel buses) and in San Francisco when I transplanted here as well. The buses that run on trolleys are pretty much called "trolley buses" here in SF, although sometimes spelled as a single word.

  16. Philip Anderson said,

    April 27, 2022 @ 7:03 am

    @Philip Taylor
    “Can’t be arsed” is British slang, but still considered vulgar by many. Meaning “I can’t be bothered to get off my arse” to do something.

    ‘Can't be arsed dates from at the very least 1968, where it appeared in Hunter Davies' authorised biography of The Beatles, in a Paul McCartney quote:

    "If they can't be arsed awaiting for me, I can't be arsed going after them. So I sat down and watched telly."
    As semi-vulgar slang, it will have been used in speech much before first appearing in a book.’

    N.B. Trams have been running again in London since 2000.

  17. john burke said,

    April 27, 2022 @ 9:44 am

    @jaap; "Lunar" is the name for a type of illuminated signal governing movement, analogous to a traffic light. Rather than regulating turn-taking at right-angle intersections, rail signals' chief function is to maintain a safe distance between trains moving on the same track, including those moving in the same direction. Signal systems often include a feature that informs an operator of whether the next section of track is occupied, so "clears the lunar" would mean "don't move forward until the signal light tells you the next strertch is unoccupied."

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