1. http://data.gov.uk/dataset/naptan. http://data.gov.uk/dataset/naptan.
2. http://data.gov.uk/dataset/road-accidents-safety-data. http://data.gov.uk/dataset/road-accidents-safety-data.
3. www.transtats.bts.gov/DatabaseInfo.asp?DB_ID=110. www.transtats.bts.gov/DatabaseInfo.asp?DB_ID=110.
4. www.transtats.bts.gov/DatabaseInfo.asp?DB_ID=120. www.transtats.bts.gov/DatabaseInfo.asp?DB_ID=120.