I’d say @joseph_125’s statement pretty much summed up why MH wasn’t really used around here either. They were expensive to maintain and operate, so they were often reserved for special situations, such as downtowns, business districts, private developments etc. where aesthetics/better color rendition were desired.
Meanwhile had CMH come out much sooner for roadway use, we may have seen it more widespread as those did negate some of the disadvantages of conventional MH lamps, while offering better efficiency and improved color rendition. However it was simply too late, the writing was already on the wall because of LEDs.
Metal halide is less expensive to operate than mercury vapor. Mercury vapor is significantly less efficient than metal halide (but not as efficient as HPS). But yes, they are more expansive to maintain and they don’t last as long.
Also, MH lamps don’t usually fail violently except for low wattage PSMH lamps (some do, though). They were found a lot in business districts, private developments, and on and in businesses for a long time. They weren’t usually even found in subdivisions, mainly like on the outside of apartments or something like that, and if used, they weren’t normally cobra heads, they were shoebox lights or acorn post tops.
Also, CMH cobras are even rarer than QMH cobras in most cases.
Also, we don’t need every MH lamp to be CMH, and not all MH lamps explode (it’s not extremely common for most variations). Probe start lamps tend to actually explode less than PSMH lamps (especially PSMH lamps ranging from 50 to 150 watts). Ceramic metal halide is expensive and they often don’t last as long as HPS (many have similar lifespans to standard PSMH pulse start lamps), though I’ve seen some go up to 24,000 hours, and Chicago, IL had so many failures with the CMH fixtures, so that was an issue too. If all cities went to CMH, they’d pay a LOT of money just to replace them because the lamps are highly expensive (especially higher wattage ones), and I don’t think cities can use 100W CMH for all their lights, some parts would require 250W or 400W lamps to get sufficient brightness. You can’t use 100W CMH for a highway.
In general, electronic HID ballasts seem less reliable than magnetic ones (kind of like fluorescent ballasts), and many CMH lamps require an electronic ballast. If cities used probe start for street lights, it’d be just fine, they may not last as long, but cities used incandescent street lights at one point (which had significantly shorter lifespans than metal halide).
Nowadays, there is no point of using MH or CMH as street lights as we already have LEDs which are more efficient and last longer than MH, and have a comparable or better CRI. I actually like that the LEDs are full cutoff, as that design puts the most light on the road and sidewalk, and the least on the sides and up. I like 4000K the best for street lights (though I prefer 5000K for anything else). LEDs probably last longer than MV if properly designed (because LEDs do not experience the same lumen depreciation as MV normally). The primary issue with mercury vapor was that over time, they’d get dimmer and eventually they’d get so dim that they’re only as bright as a 15W incandescent. LED lights also cannot explode.
