1. Oral sources
2. Interview no. 1 – An official at the Estonian Road Agency (interviewed on 15 August 2016)
3. Interview no. 2 – Police officers (three persons) (interviewed 30 August 2016)
4. Interview no. 3 – A police officer (interviewed on 30 August 2016)
5. Interview no. 4 – Two officials at the Estonian Road Agency (interviewed on 16 November 2016)