A further 20 drivers were fined for flashing their headlights at motorists approaching the police mobile speed traps from the other direction.
Pc Antony Gray, of Lancashire Police's road policing unit, said: "People who flash their headlights at other cars to warn them that there are police officers nearby may think that they are doing someone a favour but potentially they are putting lives at risk.
"The difference of a few miles per hour can mean the difference between life and death - the risk of death is approximately four times higher when a pedestrian is hit at 40mph than at 30mph.
"Flashing your lights at someone may make them slow down for just a second, but it will not make them change their habits in the long run.
"Speeding motorists need to be stopped and spoken to by officers so that they will seriously consider their irresponsible driving behaviour and hopefully drive more appropriately in the future - particularly in residential areas and near schools."
He said the majority of those fined for flashing their lights were aged over 40 and from the local area.
"It is disappointing that even though they are aware of the issues with speeding in their neighbourhood they were deliberately trying to help people avoid being spoken to by the police and thus exacerbating the problem," Pc Gray added.
Sean Corker, from the Drivers' Alliance, said: "If the outcome is drivers slow down, I don't see how they can fine others for doing this.
"Drivers have to be given notice they are in an area with speed checks - I don't think there's a difference between a road sign and a person giving a warning."
A spokesman for the AA added: "I think it is a legal and moral minefield. A lot of people will have a lot of different views on this and what is social behaviour and anti-social behaviour.
"It is very difficult. If someone is shoplifting and someone else tells them a store detective is about is that aiding and abetting or stopping them stealing?
"I think in many of these cases the police are being overly sensitive."
Chris Sweetman, a solicitor specialising in road traffic law, said he believed those caught had grounds to challenge their fines.
He said: "I think this is an underhand and unnecessary way to pick on motorists and raise revenue.
"They are not obstructing the police because they are not trying to prevent them catching a criminal, they are warning someone who is potentially going to commit a crime."
In January last year Michael Thompson, 65, was convicted of obstructing a police officer in the execution of his duty after he was caught flashing his headlights at oncoming motorists to warn them of a police speed trap ahead.
The pensioner argued that he was warning drivers for safety reasons as he had been in a crash previously when two drivers in front of him braked sharply after seeing a speed trap.
However, Mr Thompson, of Grimsby, Lincs, was found guilty after a trial at Grimsby Magistrates Court and ordered to pay £440 in fines and costs.
The Highway Code states that a driver should only flash their headlights to let other road users know they are there.
It also states that headlights should not be used to convey any other message or intimidate other road users.