The cameras will track the speed of drivers travelling between Bramham and Tadcaster Bar, with anyone travelling at more than 40mph on average being issued with a ticket.
They had not been activated yesterday but are due to be operational throughout the works, which are scheduled to last between two and three months.
The work between Bramham and Tadcaster Bar represents the first phase of the scheme, with a second due to follow on the section between Bramham Bar and Askham Bar.
The spokeswoman said the cameras were temporary features and not connected to an ongoing feasibility study into the potential benefits of introducing fixed speed cameras on the road.
It follows concerns about the number of collisions on the route, with 16 fatal crashes and 89 serious crashes in the past five years.
There are currently no fixed cameras on North Yorkshire’s road network and police instead use a fleet of safety camera vans.
The 12 vans not only detect speeding drivers, but can also identify seatbelt offences and drivers using mobile phones.