New U.S. and Canadian speed limits for oil trains will do little to temper the likelihood and severity of explosive accidents that have grown in frequency over the past two years, critics of new regulations said on Friday.

Walking a line between increasing safety and keeping oil shipments moving at a clip on North American rails, regulators announced a 50 mile per hour (mph) speed limit for oil trains, a key component of new rules rolled out on Friday. But speed was not identified as a key factor in recent crashes, and slowing trains further may congest an already beleaguered rail system, some say.

The speed provisions alone are expected to have little impact on oil train accidents, four of which have already occurred this year. Of the nine major oil train accidents in the United States and Canada since 2013, none of the trains were traveling above 50 mph, according to government records and data compiled by Reuters.

The average speed of these last accidents was 34 mph. Four of the nine occurred at or above 40 mph. Of the rest, all but one occurred when the train was traveling above 20 mph.

Under the new regulations, the speed limit for trains hauling older tank cars in urban areas would fall to 40 mph. The limits were part of a set of preliminary proposals put forward in August.

“Even with these rules in place, the accidents earlier this year would not have been prevented,” said Jared Margolis, an attorney at the Center for Biological Diversity in Portland, Oregon, which has called for a moratorium on oil trains until more stringent tank car standards are in place.

Friday’s rules called for the phase-in of tougher tank car standards including thicker hulls, head shields to protect the end of each car and electronic pneumatic brakes.

Although speed was not necessarily a factor in recent accidents, experts say that tank cars are more prone to puncture as train speeds exceed 10 mph. Data show that the faster a crude oil train travels, the more likely it is for cars to puncture on impact.

In New Augusta, Mississippi, in January last year, an oil train traveling at 45 mph came off the rails and 25 tank cars spilled oil. In Lynchburg, Virginia, a train came off the rails in April 2014 going about half as fast and only two cars ruptured, catching fire.

While the railroads have immediately voiced opposition to adopting the new braking systems that they say are expensive and potentially unreliable, the speed restrictions appear to be less contentious. Indeed, some railroads have already reduced speed limits for oil trains in urban centers to 35 mph.

Others say it will not make a difference to accidents, but reducing speeds below the new rules could hurt the rail industry.

“If you reduced speeds down to 30 mph, you would not have a corresponding drop in accidents,” said Anthony Hatch, owner of New York-based transportation consultancy ABH Consulting. “But it would severely crimp the capacity of a vitally important part of the economy.”