The event was attended by Cambodian Prime Minister Samdech Techo Hun Sen and Vietnamese Ambassador to Cambodia Nguyen Huy Tang.
Construction of the 135km road is projected to complete in 48 months and cost US$1.35 billion.
The road is Cambodia's second expressway after the Phnom Penh-Sihanoukville Expressway, which opened to traffic last year and connects the capital with the country's main port on the Gulf of Thailand.
Viet Nam-Cambodia trade value
By the end of last year, Viet Nam had 205 investment projects worth US$2.94 billion in Cambodia, establishing itself as the biggest ASEAN investor and one of the five biggest foreign direct investors there./.