National Highway 4C () is a national highway in HàGiang province in northern Vietnam. It links HàGiang City with the highland areas of the Dong Van Karst Plateau Geopark and includes the road section over Mã PàLèng Pass. The highway is widely associated with the route commonly known as the "Happiness Road" (), built from 1959 to 1965 as a road-access project for the plateau areas.
National Highway 4C runs from HàGiang City north and east across the province's karst plateau, connecting Quản Bạ, Yên Minh, ÃÂá»Âng VÃÂn, and Mèo Vạc. Tourism coverage has treated the "Happiness Road" corridor as roughly 184âÂÂ185 kilometers, while later rehabilitation planning has treated Highway 4C as roughly 200 kilometers of roadway targeted for repair and selective widening in steep terrain.
A core scenic segment runs across the ÃÂá»Âng VÃÂn plateau and is closely associated with the Dong Van Karst Plateau Geopark, which is part of the UNESCO Global Geoparks network. The best-known pass section is the road over Mã PàLèng Pass, overlooking the gorge of the Nho Quế River, with viewpoints along cliffside alignment above the river corridor.
Before large-scale road construction, travel between highland communes and market towns in the plateau areas relied largely on footpaths and packhorse tracks. The main construction period of the "Happiness Road" project is dated to 1959âÂÂ1965, providing road access from HàGiang City to plateau areas including ÃÂá»Âng VÃÂn and Mèo Vạc.
The project mobilized youth volunteer brigades and civilian labor from ethnic minority communities along the route corridor. VietnamPlus has listed participation by laborers from multiple ethnic groups, including the Hmong, Tày, Dao, Nùng, Pu Péo, and Lô Lô. Work on the plateau included extensive manual rock cutting in steep terrain, particularly on cliffside segments near Mã PàLèng Pass.
Reporting tied to the 2009 national-monument recognition of the Mã PàLèng landscape has stated that more than 1,000 youth volunteers and local residents were mobilized at the Mã PàLèng worksite and described the pass segment as taking nearly two years to complete because of sustained cliffside rock cutting above the Nho Quế River gorge. In 1961, Ho Chi Minh referred to the project as the "Happiness Road". A 1994 Bradt guidebook stated that the road through Mã PàLèng Pass was being repaired after sustaining damage described as coming from Chinese artillery.
The highway's Mã PàLèng landscape section was listed as a national monument in 2009 under Vietnam's cultural heritage administration, a designation used in provincial tourism promotion and management of viewpoints along the pass corridor.
Repairs and upgrading work have included stabilization and rehabilitation in steep terrain. Government planning published in 2025 described repair work and selective widening intended to improve safety and capacity, including segments planned for widening and the application of different technical classes depending on terrain constraints.
The pass section at Mã PàLèng Pass includes narrow mountain-road alignment, sustained exposure above a gorge, steep gradients, and tight curves, increasing technical demands for drivers in fog and heavy rain.
National Highway 4C forms part of the road network marketed to visitors as the backbone corridor for the travel circuit known as the HàGiang Loop. The plateau corridor is linked in tourism promotion to karst scenery, upland towns, and viewpoints over the Nho Quế River gorge, with Mã PàLèng treated as a signature stop.
Provincial tourism plans have treated visitor growth as an economic priority, with VietnamPlus reporting a provincial target of about 3.5 million visitors for 2025 and reporting more than 848,000 arrivals in the first quarter of that year.
Expanded travel services on routes using Highway 4C have included guided trips marketed as "easy rider" services, in which local drivers operate motorcycles while visitors ride as passengers. A separate policy strand has addressed funding for infrastructure and conservation in geopark areas, including discussion of fees for overnight stays in the geopark area.
In addition to the 2009 national-monument listing for the Mã PàLèng landscape section, Vietnamese reporting has described commemorative efforts tied to the construction period, including the placement of markers and monuments associated with the youth volunteer brigades who worked on the plateau road corridor. A 2014 report in Nhân Dân described plans for a monument to the youth volunteers at Mã PàLèng in connection with anniversary commemorations of the Happiness Road construction period.