Thai highway network
The Thai highway network follows the left-hand traffic rule of the road. The network is the twin responsibility of the Department of Highways (DOH, , "Krom Thang Luang"), and the Department of Rural Roads (DORR, , "Krom Thang Luang Chonnabot"), under the oversight of the Transportation ministry of Thailand. Public highways (, "thang luang") are also called public roads (, "thanon luang"), especially when part of urban streets. The network spans over 70,000 kilometers across all regions of Thailand. Most are single carriageways. Dual carriageways have frequent u-turn lanes and intersections slowing down traffic. Coupled with the increase in  the number of vehicles and the demand for a limited-access motorway, the Thai Government issued a Cabinet resolution in 1997 detailing the motorway construction master plan. Some upgraded sections of highway are being turned into a "motorway", while other motorways are not being built from highway sections. Types of highways. The 1992 Highway Act (), revised as the 2006 Highway Act (), defines the following five highway types: A special highway () or motorway is a high capacity highway designed for high speed traffic, for which the Department of Highways carries out construction, expansion, upkeep and repairs, and is registered as such . Motorway entrances and exits have controlled access, and controlled by the DOH. Registration of motorways is overseen by the Director General of the DOH. A national highway () is a primary highway, part of the network connecting regions, provinces, districts, and other important destinations, for which the DOH carries out construction, expansion, upkeep and repairs. Registration of national highways is overseen by the Director General of the DOH. A rural highway () or rural road is a highway for which the Department of Rural Roads carries out construction, expansion, upkeep and repairs. Registration of rural highways is overseen by the Director General  of the DORR. A local highway () or local route is a highway for which the local administrative organization carries out construction, expansion, upkeep and repairs. Registration of rural highways is overseen by the provincial governor. A concession highway () is a highway for which a legal government concession has been granted. Registration of concession highways is overseen by the Director General of the DOH. Highway numbering. The first digit of a highway number indicates the region of Thailand it serves, with the number of digits indicating the highway classification. These regions are: A single digit indicates one of four highways connecting  Bangkok to outlying regions: Two digits indicate a principal highway within a region, such as Route 22 in the northeast between Udon Thani and Nakhon Phanom. Three digits indicate a regional secondary highway, such as northeastern Route 202 between Chaiyaphum and Khemarat, and central Route 314 between Bang Pakong and Cha Choeng Sao. Four digits indicate an intra-province highway connecting a provincial capital to its districts, or between important sites, such as northern Route 1001 between the Route 11 intersection and Amphoe Phrao, and southern Route 4006 between the Route 4 intersection (Ratchakrut) and Lang Suan. Department of Highway  signage. Route number signs. DOH signs for public highways (ทางหลวง, "thang luang") are white squares with a black garuda (ครุฑ khrut) centered above the route number. Department of Rural Roads. DORR rural roads do not follow the regional numbering scheme, above. Signs may be black-on-white or gold-on-blue, with a two-letter province designation prefixed to the road number. Depicted is SK. 3015, for a rural road in Songkhla Province. The rural road network measures some 35,000 km, about 82 percent of which is paved. The Department of Rural Roads of the Ministry of Transport takes care  of the maintenance of all the rural roads in Thailand. Kilometer stones. or () single-carriageway kilometer stone facings display the route number on the outline of a garuda. Some kilometer stones also display the route number on top. Those located to the left of the carriageway display kilometers remaining to the road's beginning at kilometer 0. As seen on the right from the opposite lane, the kilometer stones ascend in value as one proceeds away from kilometer 0. On edges facing traffic, DOH kilometer stones usually show distances remaining to the next two towns, (amphoe seats, or provincial capitals .) Some edges, such as the one depicted to the left, have retroreflector panels. Dual carriageway kilometer stones or posts in the median strip show only the kilometer number.