A crude-only Canadian Pacific train carrying North Dakota crude passed through St. Paul along Warner Road and the Mississippi River. (The Minnesota Star Tribune)

As U.S. senators — one from Minnesota and one from Wisconsin — we have always understood how important railroads are to the economy in each of our states. Our businesses and farmers rely upon rail service as a reliable way to move their products to markets across the country and around the world.

But on Wednesday, at a meeting in Minneapolis, we'll hear from residents and local officials who have deep concerns about the dramatic expansion of rail cars carrying highly volatile and flammable crude oil from the Bakken oil fields in North Dakota through Minnesota and Wisconsin to refineries in other states.

While the quick growth in oil trains has meant higher profits for the large railroads and skyrocketing tax revenue for the state of North Dakota, it also has put hundreds of communities in Minnesota and Wisconsin at risk for the explosive crashes that come when an oil train derails.

In the past seven months, there have been at least six serious oil train accidents in North America — including a fiery explosion in North Dakota that forced the evacuation of a small town. Another train carrying Bakken oil exploded in Quebec a few years ago, killing 47 people.

We are thankful our states have not experienced similar tragic accidents, but with hundreds of thousands of residents living within a half mile of tracks carrying oil trains, we know we can't allow the safety of our communities to be simply a matter of luck. That's why for more than a year, we've taken an all-of-the-above approach to ensure that oil trains travel more safely.

In August, when the Senate passed a bipartisan transportation bill, we pushed to include provisions to safeguard communities along oil train routes by requiring that railroads develop plans to quickly respond to oil spills. The bill also requires that carriers make oil train information available to local first responders so that they are aware when such trains are traveling through their communities. And finally, for the first time, it would give state and local officials access to inspection reports for private bridges owned by the railroads.

Beyond legislation, we've also pressed the railroads as well as federal transportation and safety officials to protect communities along rail lines from oil train dangers. And while we've already seen some good steps implemented to improve safety, it's clear that more needs to be done.

First, we've called for safer tank cars and for the rerouting of trains that are carrying this highly explosive oil through populated areas. We've also pressed to make sure that the volatility of the crude itself is reduced to make it safer before it's loaded onto the trains.

In response to our calls for action, the U.S. Department of Transportation has taken some useful steps to help keep our communities safe. In May, it announced new standards for trains carrying flammable fuels.

The rules require that new tank cars have thicker shells and other improvements to make them safer in the event of a derailment. And within five years, all trains carrying crude will have to meet this standard. While this is a step in the right direction, we can't slow-walk the rollout of safer tank cars, and we will continue to push to make this happen more quickly.

We also know that the light crude oil passing through our states each day from North Dakota is much more volatile than heavier crudes produced elsewhere. That's why we've supported efforts to reduce the volatility before it is shipped through our states.

Producers can actually condition the crude at the well, where they can get rid of a lot of the volatile natural gas liquids. In fact, in April, the state of North Dakota started requiring them to do just that. But we'll be pushing our federal regulators to reduce volatility even further to make sure we get the strongest possible protections for people in our states.

The new federal rules also include requirements to reduce operating speeds and to improve routing decisions so that when oil trains can avoid the most populated areas, they do.

We also want local officials and first responders to have as much information as possible about oil being shipped through their communities. While the new rules require railroads to share information about oil shipments, that information often doesn't make it to local communities. Because of that, we've urged the Transportation Department to strengthen disclosure requirements. It has responded with a promise to do just that.

Railroad service is an important part of our states' transportation infrastructures and is critical to our economy. That's why we'll continue to do everything we can to safeguard communities in Minnesota and Wisconsin from the dangers posed by the unprecedented expansion of volatile crude oil being shipped through our states.

Al Franken represents Minnesota and Tammy Baldwin represents Wisconsin in the U.S. Senate. Both are Democrats.