The existing road networks of Irosin provide access to all its rural barangays to the urban center except for Cawayan, a mountain village. The Maharlika Highway is a main road artery linking the municipality to other places in the Philippines. The existing roads are classified into national, provincial, municipal and barangay roads. The national road has a length of 22.155 kilometers stretching from Bolos in the north to Casini in the south and from town center to Mapaso in the east. The provincial road in the municipality includes the Gulang-Gulang to Gabao road, Buenavista to Batang road and Bolos to Guruyan road with a total length of 5.945 kilometers. The existing roads within the poblacion are municipal roads with a total length of 7,927 kilometers. The roads classified as barangay roads have a total length of 51.621 kilometers. There is a private road leading to Mt. Jormajan with a total length of 1,399 kilometers. The total length of the road network in the municipality is 89.047 kilometers.
As to the type of road surface in 2014, 100% of the national roads are Portland Cement Concrete Pavement (PCCP) and with Asphalt Armoring at Maharlika Highway. The whole length of the provincial roads and municipal roads are concreted. Only 58.3% of barangay roads are concreted while the remaining 41.7% are unpaved with gravel and earth surfacing. There are fifteen 15 bridges in the municipality and majority of which is along the national roads. Eleven bridges are permanent concrete bridges and four are spillways reinforced by culverts. Majority of the bridges has 15-ton load capacity.
Irosin is accessible to all means of land transportation being at the midway of the province. Public transport buses and other public utility vehicles plying the Manila to Southern Bicol, Samar, Leyte, Masbate and Mindanao route regularly passes Irosin. They have established pick-up stations or booking offices as well as terminals in the municipality. The adjoining towns of Bulan and Matnog where seaports for roll-on roll-off vessels are present and the transit point to Masbate, Visayas and Mindanao are 20 kilometers and 23 kilometers away respectively.
The central location of Irosin in the Sorsogon province made the town a catchment area and a host to several public and private institutions catering to a number of barangays of at least five adjoining towns of the province. The town also is a convergence area of economic activities of the towns of Bulan, Bulusan, Juban, Matnog and Sta. Magdalena. The mode of transportation in the inter-barangay mobility of people and products are mainly tricycles, jeepneys and trucks except for Cawayan – a barangay situated in the highland with no road serviceable to motorized vehicles. Tricycles are the most common mode of public transportation in the town proper. A road network system connects almost all the barangays to the Maharlika Highway and other national roads traversing the town. Land transportation facilities in the municipality include a public transport terminal for jeepneys and tricycles along the sides of the public market, a private bus terminal, and four gas refilling stations. There are also automotive repair and vulcanizing shops for emergency and minor vehicle repairs.