Admins / mods: Please edit this post whenever any info is incorrect or outdated, and post at the end of the thread indicating what change(s) you've made.
Let's keep all the info easy to find right here at the start of the thread.
Please note: This list is only meant to show who maintains existing systems. There's no implication that a given collaborator will start development of future systems not yet in development. For example, yakra maintains AR, but has no interest in developing the AR state highways.
Africa
AGO, BDI, BWA, COD, DZA, EGY, GAB, KEN, LSO, MOZ, MWI, MUS, MYT, NAM, NGA, REU, RWA, SEN, SWZ, TUN, TZA, UGA, ZAF, ZMB, ZWE - si404
ESH, MAR - panda80
Asia
Western Asia:
ARM, AZE, CYP, GEO, IRN, ISR - si404
TUR - panda80
Mashraq:
ARE, BHR, IRQ, JOR, KWT, LBN, OMN, PSE, QAT, SAU, SYR, YEM - si404
Central Asia:
AFG, KAZ, KGZ, PAK, TJK, TKM, UZB - si404
South and East Asia:
BGD, CHN (all regions), HKG, KOR, LKA, MGL, NPL, PRK, TWN - si404
IND - Bickendan
JPN - nezinscot
Southeast Asia:
BRN, IDN, KHM, LAO, MMR, MYS, PHL, SGP, THA, VNM - si404
Europe
Islands of the North Atlantic:
ENG, FRO, IMN, IRL, JEY, NIR, SCT, WLS - si404
ISL - Duke87
France:
FRA-ARA, FRA-BFC, FRA-BRE, FRA-CVL, FRA-GES, FRA-HDF, FRA-IDF, FRA-NAQ, FRA-NOR, FRA-OCC, FRA-PAC, FRA-PDL - michih
FRA-COR - si404
Iberia:
AND, ESP-AN, ESP-AR, ESP-AS, ESP-CA, ESP-CB, ESP-CL, ESP-CM, ESP-CT, ESP-EX, ESP-GA, ESP-IB, ESP-MC, ESP-MD, ESP-NC, ESP-PV, ESP-RI, ESP-VC - si404
PRT - michih
Northern Europe:
ALA, EST, FIN, LVA - si404
BEL, DNK, LTU, LUX, NLD, NOR, SWE - michih
Central Europe:
AUT, CHE, CZE, DEU (all regions), LIE - michih
POL, SVK - si404
Southern/SE Europe:
ALB, BGR, BIH, GRC, ITA, MKD, MLT, MNE, RKS, SRB - si404
HRV, SVN - michih
HUN, ROU - panda80
Eastern Europe:
BLR, CRM, MDA, RUS, UKR - si404
North America
United States
AK - oscar
AL - froggie
AR - yakra
AS - si404
AZ - Duke87
CA - oscar
CO - the_spui_ninja
CT - yakra
DC - Duke87
DE - Markkos1992
FL - rickmastfan67
GA - ntallyn
GU - no specific maintainer -- anybody/everybody/nobody
HI - oscar
IA - Highway63
ID - compdude787
IL - Highway63
IN - mapcat
KS - yakra
KY - mapcat
LA - mapcat
MA - yakra
MD - Duke87
ME - yakra
MI - mapcat
MN - froggie
MO - Highway63
MP - no specific maintainer -- anybody/everybody/nobody
MS - froggie
MT - the_spui_ninja
NC - mapmikey
ND - the_spui_ninja
NE - yakra
NH - yakra
NJ - yakra
NM - oscar
NV - oscar
NY - yakra
OH - mapcat
OK - yakra
OR - Bickendan
PA - Markkos1992
PR - mapcat
RI - yakra
SC - mapmikey
SD - Highway63
TN - mapcat
TX - yakra
UT - Duke87
VA - mapmikey
VI - Duke87
VT - froggie
WA - compdude787
WI - Highway63
WV - rickmastfan67
WY - the_spui_ninja
Canada
AB - yakra
BC - oscar
MB - yakra
NB - yakra
NL - yakra
NS - yakra
NT - oscar
NU - N/A
ON - rickmastfan67
PE - yakra
QC - oscar
SK - oscar
YT - oscar
Mexico
MEX-AGS - (no data yet)
MEX-BC, MEX-BCS, MEX-CAM,
MEX-CHIH, MEX-CHIS, MEX-COAH, MEX-COL,
MEX-DF, MEX-DGO, MEX-EMEX, MEX-GRO,
MEX-GTO, MEX-HGO, MEX-JAL, MEX-MICH,
MEX-MOR, MEX-NAY, MEX-NL, MEX-OAX,
MEX-PUE, MEX-QRO, MEX-QROO, MEX-SIN,
MEX-SLP, MEX-SON, MEX-TAB, MEX-TAM,
MEX-TLAX, MEX-VER, MEX-YUC, MEX-ZAC - neroute2
Caribbean and Atlantic
ABW, BRB, CYM, GLP, JAM, MAF, MTQ, SPM - si404
BLZ - mapmikey
GTM - neroute2
Oceania
AUS-ACT, AUS-NSW, AUS-NT, AUS-QLD, AUS-SA, AUS-TAS, AUS-VIC, AUS-WA, NCL, NZL, PYF, WLF - si404
South America
ARG, URY - michih
CHL, ECU - neroute2
GUF - si404
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I've gone with forum usernames instead of real names, so forum readers can easily know who's who.