Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_3005999_1 ( route_number VARCHAR, origin VARCHAR, destination VARCHAR )

### Question ###
How many route numbers occur for the origin of Birmingham and destination of Bristol?

### Accurate SQL ###

SELECT COUNT(route_number) FROM table_3005999_1 WHERE origin = "Birmingham" AND destination = "Bristol"