Wow. I agree with VF, some of the responses so far have been.... interesting.
It is certainly a Common Musk, AKA Stinkpot. Stinkpots do not STINK, but they DO secret a smelly musk if STARTLED. I have a Stinkpot in a 54 gallon aquarium in my living room, and I assure you, despite the name "Stinky," he does not smell.
Painted turtles and Sliders make HORRID PETS compared to a mud or musk turtle. Captive born muds or musks are wonderful turtles to keep in the house. They are lucky to reach 6" in length, while a painted or slider is lucky to stay less than 12". The amount of space and filtration that a slider, snapper, or other pond turtle needs is MAMMOTH to put it simply.
Mud turtles do not often leave the water. They are like snappers, and prefer to bask in the shallows rather than perfectly dry, like a pond turtle. If this was found on the road, I again agree with VF that she is probably looking for a place to lay her eggs. Please take her to a place where there is a still water pond, with lots of plants in and around the water and let her go. If you want a Stinkpot as a pet, or other mud turtle, such as an Eastern or a Three lined (which I also have) please check the classifieds on kingsnake.com for a captive bred baby. They can be purchased for $20 or less. No need to take wild turtles from the wild. Not allowing this female to be free to lay her eggs could cause her to become egg bound and die. They will retain their eggs if conditions are not ideal or if they are stressed.
