Lincolnshire County Council was considering whether to lower the 50mph stretch near East Heckington to 40mph.
However, councillors feared that it could lead to dangerous overtaking the moment vehicles left the zone.
It would extend from the junction with Sidebar Lane through the village and almost to Swineshead railway station.
The council’s Planning and Regulation Committee said the proposed speed reduction needed a rethink.
Councillor Alison Austin said: “I have concerns about the extent to which traffic would be kept to 40mph. This is a major road in the East Midlands with a large amount of heavy traffic.
“I’m worried that once traffic leaves 40mph, all hell will break loose. Everyone is going to be jockeying to get past each other.
“With it being such a long, long stretch, there could be unforeseen consequences the moment vehicles are out.
“The A17 tends to be self-regulating – this won’t be the case at 40mph.”
Councillor Thomas Ashton agreed that it did not seem appropriate, saying: “There are sections that don’t feel like 40mph – there are bits of open road with good visibility.”
Speed surveys found that traffic averaged between 42 and 46 mph in the stretch.
Councillor Paula Ashleigh-Morris, who represents a Boston ward, also said that the change did not seem needed.
“I was surprised to find there were only 15 accidents resulting in injuries on this stretch in the last five years,” she said.
“We have very few good roads into Boston – this one cracks along.
“Where I live on a B road in Langrick, we’ve had considerably more accidents as HGVs head up to Immingham. This change needs a rethink.”
Councillor Ian Carrington also requested for information on whether speed had contributed to previous accidents.
Members voted for council officers to take another look at reducing the extent of the 40mph zone.