It was supposed to be a landmark trial that could lead to the creation of Norfolk's first 20mph town.
But campaigners have branded the measures to come into force next month in Swaffham as "laughable and ridiculous" after it was revealed only one road will see any changes.
Locals have waited more than a year for the trial to come into effect, which was meant to gather evidence to be used to support a permanent introduction on most of the roads.
It comes amid growing volumes of traffic driving along the high street, with HGVs passing through at a rate of one every two minutes.
However, from late February, there will only be one change - an extension of the 20mph limit already in force on London Street to include the full length of the road up to the north end of Brandon Road.
The experimental traffic order will be monitored for six months, which Norfolk County Council say will help determine whether it is the "right solution" for Swaffham.
A spokesman for Norfolk County Council said: "Once we have the evidence from this trial, we’ll be able to make an informed decision on whether the new limit should stay in place indefinitely.”
But for Tony White, who has led the 20 is Plenty crusade for the market town, the trial is too limited in scope and he has questioned what will be achieved.
He said: "This is something that the vast majority of residents and the town council support - we want to make the town a safer environment for everyone.
"But we need an area-wide trial to see what difference it makes. It is laughable and ridiculous."
The campaigner also fears motorists will simply avoid it altogether and use side roads instead.
He added: "A 20mph speed limit in Swaffham is the will of the people. We need to create a better environment for the people of the town."
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