The derailment and explosion of a train of oil-tank cars in North Dakota last week was the fourth such wreck in North America in under six months.

No one was injured in the small North Dakota town of Casselton, but they mayor there attributed that to luck rather than successful safety precautions.

In November, an oil-laden train spilled thousands of gallons of crude oil into an environmentally sensitive marsh, where the damage was contained only because of a nearby beaver dam.

A month earlier a train carrying propane and oil derailed in Gainford, Alberta, Canada, forcing the evacuation of the town.

Last July, a train carrying 50,000 barrels of crude oil rolled uncontrolled for eight miles, crashed and exploded in Lac-Megantic, Quebec, killing 47 people and nearly destroying the town.

Accidents have risen along with North American production of crude oil, which has risen in the United States by 2 million barrels per day over the last two years. Railroads now haul 90 percent more crude oil in the United States and Canada than they did in 2009, and the accident rate demonstrates that safety measures are needed.

U.S. and Canadian transportation officials should mandate use of railroad oil tankers that don't puncture easily on impact, and impose speed restrictions that allow train crews more time to respond to problems.