Switching off street lights at night creates an “insidious threat” to safety, according to the president of the AA.
The organisation has published figures on accident rates, which show a sharp fall in incidents in lit 30 and 40 mph zones in bad weather.
This contrasts with only a small fall in accidents in the equivalent unlit roads.
Edmund King said: “Worse accident rates on roads with street lights turned off or not present are an insidious threat that has crept in literally under the cover of darkness.”
“Roads that are safe when lit can become unsafe with the lights switched off, but that is only shown when drivers, cyclists, bikers and pedestrians start to get hurt and killed.
“Why did people have to become street light victims to prove the point?
“With an extra casualty here and there, it is difficult to spot a creeping overall trend that might suggest something is dangerously wrong with a blackout.
“Without more switched-on thinking, a 70% street-light blackout in Essex and other councils will certainly cut costs and save CO2 but it will be paid for in lives and injuries.”
Essex County Council first switched off 70 percent of street lights on January 13 from midnight to 5am as part of a move to save £1.5m.
Last month the county council changed the timings in Epping Forest from 1am until 6am because of fears over the safety of late-night Tube users.
An Essex County Council spokesman said: “Consultations around the introduction of part-night lighting for the county have taken place since September.
"This has given parish and town councils, district councils, county councillors and the emergency services the opportunity to make any requests for areas that should not be included in the scheme.
"We have ensured those lights which meet the exception criteria are excluded from the scheme such as town centres, key road junctions and accident cluster sites."