The site is undergoing major refurbishment works with new toilets being installed.
They will remain free-to-use for the remainder of January. From then on a 20p charge will be required.
Council bosses say the move is "in line with other bus and railway stations around the country" and will help cut down on anti-social behaviour.
Change machines have been installed outside the entrance to the new toilets to help visitors out, they added.
Work is continuing on the redevelopment of the concourse, with more sections now completed.
The latest improvements include new internal coach facilities, information desk and security office.
County Coun Keith Iddon, cabinet member for highways and transport, said: "We're really pleased with the redevelopment work in the concourse and we've already had lots of comments from people about how good it now looks.
"We know that these toilets will be a big improvement on what we had before, with better facilities for people to use. Toilet charges are quite normal at bus and railway stations around the country. People who travel to other places will be familiar with this.
"A small charge helps with the upkeep, reduces the running costs and helps to reduce anti-social behaviour.
"Our multi-million pound redevelopment is progressing well. The concourse has been renovated in keeping with the Listed status and the bus stands have been updated. As a Listed building, we have a responsibility to keep it well-maintained."
The new women's toilets are located in the coach lounge area, while the refurbished women's toilets will be temporarily for use by men - until the men's toilets have been refurbished. Signage will be in place to advise customers of this new arrangement, the council added.
The 20p charge policy for the toilets will be in place from Thursday, February 1.