Electronic toll collection (ETC), locally known as the FASTag system in India, has been made compulsory for payment of tolls on all National Highways (NHs) from January 2020. The users are thus adopting the newly developed FASTag system for toll payment, but the penetration rates are very low. The present research aims at studying the factors affecting road users’ willingness or unwillingness to use the FASTag. The nationwide survey data are collected from the different vehicle users using an online survey and personal interview methods. Various trip-related parameters like vehicle type, trip purpose, etc.; attitudinal parameters like awareness of toll roads, and current toll rates; FASTag-related parameters like awareness of FASTag, and having or not having the FASTag, and socioeconomic and demographic parameters like age, gender, monthly income, etc., are considered in developing the questionnaire. Analysis of these survey data showed that drivers of big cars, Bus, multi axel vehicle (MAV) and Truck Trailers are more willing to use the FASTag facility to pay toll. A willingness to adopt the FASTag model is developed using the binary choice model. The results showed that trip-related attributes such as vehicle class, trip purpose and trip frequency significantly impact willingness to own FASTag. Further, awareness about FASTag is one of the important factors for shifting towards the FASTag system. Moreover, frequent users passing during peak hours are more likely to use FASTag. Also, the users who are in service, either Government or Private, have shown more willingness to adopt FASTag than those who are unemployed. Further, the stated preference analysis is also carried out for framing possible policy measures to increase the FASTag share. The outcome of the present study is expected to provide essential inputs to the policymakers for enhancing the adoption of FASTag among toll road users.