Halt means stop. To "bring to a halt" means to stop something or make something stop. In this case, because there is road work, traffic has stopped. Another example would be, "The protestors linked arms to form a human chain in front of the building, bringing construction to a halt."

"to a halt" can be used with different verbs too. Came to a halt. "Brought it to a halt" The bus came to a halt just in time to avoid hitting the wall. Came to a halt simply means that something stopped. The bus came to a halt just in time to avoid hitting the wall. If you want to explain that something else forced an object, activity or person to stop, then you would use brought ___ to a halt. You can also use other verbs in the phrase depending on the situation. "The car rolled to a halt when it stalled." Look into these phrases also. "ground to a halt." ; "to a grinding halt" ; "halted in mid sentence"; "Came to a standstill."