| SMN | Société Morbihannaise de Navigation | In French | |
| SNCB | Société Nationale des Chemins de fer Belges (www.b-rail.be) = NMBS | Nationale Maatschappij der Belgische Spoorwegen | In Dutch |
In French | → Rail transport engineering |
| SNCF | Société Nationale des Chemins de fer Français | In French | |
| SNCFR | Societatea Naţională a Căilor Ferate Române | In Romanian | |
| SNCFT | Société Nationale des Chemins de Fer Tunisiens | In French | |
| SOCRATE | Système Offrant à la Clientèle la Réservation d'Affaires et de Tourisme en Europe | In French | |
| SODETREL | Société pour le Développement des Transports Électriques | In French | → Electrical engineering → Vehicle engineering |
| SODIT | SOciété Développement Innovation dans les Transports | In French | |
| SPT | Service des Postes et Télécommunications (www.spt.pf) | In French | → Telecommunications |
| SPT | Société des Postes du Togo | In French | |
| SPT | Simplifying Passenger Travel (www.spt.aero) | In English | |
| SPT | Strathclyde Partnership for Transport (www.spt.co.uk) | In English | → Organizations and associations |
| SQ | Singapore Airlines | In English | |
| SRJ | Stockholm-Roslagens Järnvägar | In Swedish | |
| SRPT | Service Régional de la Police des Transports | In French | → Public administration, government |
| SRWT | Société Régionale Wallonne de Transport | In French | |
| SSF | Sveriges Segelfartygsförening | In Swedish | |
| SSR | Spårvägssällskapet Ringlinien | In Swedish | |
| SSS | Svenska Spårvägssällskapet | In Swedish | |
| ST2N | Société Nouvelle des Transports de l'Agglomération Niçoise | In French | |
| STAN | Système de Transport de l’Agglomération Nancéienne | In French | |
| STB | Surface Transportation Board (www.stb.dot.gov) | In English | |
| STI | Systèmes de Transports Intelligents | In French | |
| STIB | Société des Transports Intercommunaux de Bruxelles = MIVB | Maatschappij voor het Intercommunaal Vervoer te Brussel | In Dutch |
In French | → Organizations and associations |
| STN | Société des Transports de Normandie | In French | |
| STN | London Stansted Airport | In English | |
| STP | Syndicat des Transports Parisiens | In French | → Organizations and associations |
| STS | Siemens Transportation Systems | In English | → Vehicle engineering |
| SWOV | Stichting Wetenschappelijk Onderzoek Verkeersveilgheid | In Dutch | → Foundations |
| SYTRAL | SYndicat des TRansports en commun de l’Agglomération Lyonnaise | In French | → Organizations and associations |
| T&D | Transportation and Docking | In English | → Maintenance and logistics |
| TACAN | Tactical Air Navigation | In English | → Aeronautics, aircraft |
| TACAN | Tactical Air Control and Navigation | In English | → Aeronautics, aircraft |
| TACANS | Tactical Air Control And Navigation System | In English | → Aeronautics, aircraft |
| TACC | Tactical Air Control Center | In English | → Aeronautics, aircraft |
| TCFN | Total Compagnie Française de Navigation | In French | → 665 |
| TCN | Transportation Control Number | In English | → Vehicle engineering |
| TCSP | Transport en Commun en Site Propre | In French | |
| TDG | Traffic Design Group | In English | |
| TEA | Transport Policy Evaluation and Analysis | In English | → Politics |
| TEF | Tuluzaj Esperantistaj Fervojistoj | In Esperanto | → Organizations and associations |
| TEN-T | Trans-European Networks-Transport | In English | |
| TER | Transports Express Régional | In French | |
| TGV | Train à Grande Vitesse | In French | → Vehicle engineering |
| TIPP | Taxe Intérieure sur les Produits Pétroliers | In French | → Taxes, duties → 665 |
| TL | Tramways Lausannois | In French | |
| TL | Transports Lausannois | In French | |
| TMA | Trans Mediterranean Airways | In English | → Aeronautics, aircraft |
| TMB | Transportation Management Bulletin | In English | |
| TMB | Transportes Metropolitanos de Barcelona | In Spanish | |
| TMD | Transport de Matières Dangereuses | In French | → Chemicals |
| TMD | Transports de Marchandises Dangereuses | In French | |
| TOI | Transport Okonomik Institut | In Norwegian | → Economics |
| TRB | Transport Research Board | In English | |
| TREN | TRansport et ÉNergie | In French | → Energy economics |
| TRL | Transport Research Laboratory | In English | → Research institutes |
| TRT | Transportation Research Thesaurus | In English | |
| TSE | Transportation Support Equipment | In English | → Vehicle engineering |
| TSIS | Traffic Software Integrated System | In English | → Software |
| TTP | Transports Terrestres Promotion | In French | |
| TWU | Transportation Workers Union of America | In English | → Organizations and associations → Labour, labour economics |
| UAL | United Airlines | In English | |
| UEM | Union Européenne Motocyclisme | In French | → Organizations and associations |
| UIC | Union Internationale des Chemins de fer | In French | |
| UMCPG | Union des Mutuelles des Cheminots et des Personnels du Groupe SNCF | In French | |
| UNOSTRA | Union Nationale des Organisations Syndicales de Transport Routier Automobile | In French | → Organizations and associations |
| UPU | Union Postale Universelle = UPU | Universala Poŝt-Unio | In Esperanto = UPU | Universal Postal Union | In English |
In French | → Organizations and associations → International relations |
| UPU | Universala Poŝt-Unio = (look above) |
In Esperanto | → International relations |
| UPU | Universal Postal Union = (look above) |
In English | → International relations |
| USAP | Union des Société d'Autoroutes à Péage | In French | → Organizations and associations |
| USCD | Union Sportive des Cheminots Dijonnais | In French | → Organizations and associations → Sport, physical exercises |
| USCF | Union Sportive des Cheminots de France | In French | → Organizations and associations → Sport, physical exercises |
| USPS | The United States Postal Service | In English | |
| UTP | Union des Transports Publics | In French | → Organizations and associations |
| UVP | Unité de Voiture Particulière | In French | |
| VAL | Véhicule Automatique Léger | In French | → Vehicle engineering |
| VBA | Verkehrsbeeinflussungsanlage | In German | |
| VCÖ | Verkehrsclub Österreich (www.vcoe.at) | In German | → Organizations and associations → Vehicle engineering |
| VESTA | VErsailles Sécurité routière Technologies Avancées | In French | |
| VMIS | Verkehrsmanagement und Informationssystem | In German | |
| VNF | Voies Navigables de France | In French | |
| VOR | Verkehrsbund Ost-Region | In German | |
| VTC | Véhicule de Transport en Commun | In French | |
| VTI | (Statens) Väg-och Transportforskninginstitut | In Swedish | |
| WHIST | Walloon Highway Information System for Traffic | In French | |
| ZELT | Zone Expérimentale et Laboratoire de Trafic | In French | → Regional planning |
| ZEVGA | Zeitschrift fur Eisenbahnwesen und Verkehrstechnik Glasers Annalen | In German | → Serial publications, periodicals → Vehicle engineering |
| ZKR | Zentralkommission für die Rheinschifffahrt = CCR | Centrale Commissie voor de Rijnvaart | In Dutch = CCR | Commission Centrale pour la Navigation du Rhin | In French = CCR | Central Commission for Navigation on the Rhine | In English |
In German | |
| ΟΛΠ | Οργανισμός Λιμένος Πειραιώς & | In Greek | |
| ΟΣΕ | Οργανισμός Σιδηροδρόμων Ελλάδας | In Greek | |
| МИАТ | Монголын Иргэний Агаарын Тээвэр = MIAT | Mongolyn Irgenii Agaaryn Teever | In Mongolian |
In Mongolian | → Aeronautics, aircraft |