Can you say:
"The new one-way system is considered by most rather to be an impediment than a help."
using "rather" to mean
"The new one-way system is considered by most to be more of an impediment than a help?"
Can you say:
"The new one-way system is considered by most rather to be an impediment than a help."
using "rather" to mean
"The new one-way system is considered by most to be more of an impediment than a help?"
Your original sentence is almost there, but "rather" is in the wrong place. Try this:
The new one-way system is considered by most to be an impediment rather than a help.