Channel 19 AM on the West Coast has remained in active use as a trucker and highway information channel since about 1976.
Prior to that, Channel 10 AM was the ad hoc nationwide trucker channel, but some regional trucker channels (such as 17 AM and 21 AM) also existed then.
Channel 17 AM started as one of those regional trucker channels in California.
Then 17 AM became very active up and down the coast around 1978 during the intense skip of that roaring sunspot cycle.
Eventually, around 1996 during the low point in the sunspot cycles, most truckers in California began keeping their dial locked on 19 AM instead of switching to 17 AM when they were on Interstate I-5.
17 AM eventually stopped being a trucker channel at all, and devolved into a calling and working channel for the locals in many California towns and cities.
The addition of FM to the new FCC rules will probably cause another evolution in the use of FM for truckers and local information.
The growing use of Channel 29 as an FM Trucker Channel looks eerily similar to the way previous trucker channels evolved.
Considering how many truckers seem to already have FM-capable radios installed I can definitely see your point.
I know it's not a 1-for-1 comparison but in Russia they have 27.135 MHz AM (Channel 15AM, C15AM or D15AM) as the AM road/highway/trucker channel and 27.185 MHz FM (Channel 19 FM, C19FM or D19FM) as the FM road/highway/trucker channel. 27.635 MHz FM is also used as a highway advisory channel or road channel (D19FM or E19FM) in some areas. In larger cities, truckers use additional channels (mostly in FM mode) but Channels 15 and 19 seem to be the main channels. Rigs designed for the Russian market have Channel 15 switches like most rigs have a Channel 9 / Channel 19 / NORM switch (or just a Channel 9 switch).
Maybe something similar will happen here. FM does make more sense for local short-range communications, which is what channel 19 is used for now. Maybe 19 will eventually switch to FM and another channel will become the AM channel.
I remember reading about the 23-channel days, back when channel 9 was the emergency channel, channel 10 was the road channel/trucker channel and channel 11 was the calling channel. Channel 11 has remained the calling channel in many respects. I believe the switch from 10 to 19 was, at least in part, to reduce adjacent-channel interference on channel 9 and channel 11 from heavy traffic on channel 10.
We might end up taking a page out of the European or Russian CB book and include the mode in the channel designator - CB channel 29 FM, CB channel 19 AM, CB channel 21 AM, CB channel 31 FM, etc.
Channel 1 -
Channel 2 -
Channel 3 -
Channel 4 - this is apparently used by 4x4 groups, Jeep clubs, etc. - see also: channel 16 - AM mode
Channel 5 - heavily used by Latin American stations - AM mode
Channel 6 - we already know what channel 6 is...
Channel 7 - often similar to Channel 5, although when the band is closed its used locally - AM mode
Channel 8 -
Channel 9 - still the emergency channel, in theory, but you'll have better luck on 19. Latin American calling channel - AM mode
Channel 10 -
Channel 11 - calling channel - AM mode
Channel 12 -
Channel 13 -
Channel 14 - AM mode channel, used locally - AM mode
Channel 15 - Often also used as an AM DX channel
Channel 16 - this is apparently used by 4x4 groups, Jeep clubs, etc. - see also: channel 4 - AM mode
Channel 17 - AM DX channel, calling channel - AM mode
Channel 18
Channel 19 - road channel - highway channel - trucker channel - AM mode
Channel 20 - "testing channel" - used for DX during band openings - AM mode (for now?)
Channel 21 -
Channel 22 - used locally (around me anyway) AM mode
Channel 23 -
Channel 24 -
Channel 25 -
Channel 26 - AM DX calling channel - AM mode
Channel 27
Channel 28 - AM DX calling channel - AM mode
Channel 29 - trucker FM channel - CB channel 29 FM 27.295 MHz FM mode
Channel 30
Channel 31
Channel 32
Channel 33
Channel 34
Channel 35 - sometimes used for SSB
Channel 36 - often used for SSB, or as a local channel
Channel 37 - often used for SSB
Channel 38 - SSB calling - 27.385 MHz LSB 27.385 LSB
Channel 39 - often used for SSB
Channel 40 - AM channel, sometimes used for SSB operations as well