Is a national speed limit again on government agenda?

It seems like the idea of a nationally enforced auto speed limit is an idea that's past its due date. But there is an idea in some corners of the government and private sector to revive it.

In July when gas prices were hitting the $4 per gallon level, Senator John Warner asked the Government Accountability Office to investigate what it would mean to reinstitute a national speed limit of 55MPH. You may recall the US had a widely disregarded 55 MPH limit until 1995.

The GAO today answered Warner's request and said that while reducing the speed limit could reduce oil consumption, a variety of other factors including drivers' compliance with a reduced speed limit, would affect the actual impact of a lower speed limit.

The main issue: Reducing the speed limit does not necessarily mean that drivers will comply. In fact, in 1975, under the previous national speed limit, about half of the states reported more drivers exceeding the national speed limit of 55 MPH than complying with it. States may vary in their ability to enforce the reduced speed limit, in part due to cost and limited resources, affecting driver compliance, the GAO stated

A national speed limit would not affect many of the miles driven in the United States, such as those in urban areas, where most vehicles are already traveling at lower speeds due to lower speed limits or congestion. Less than one quarter of the vehicle miles traveled in the United States would likely be directly affected by a changed speed limit. In addition, congestion forces some vehicles to travel slowly, no matter what the speed limit, meaning a reduction would have little or no impact on fuel consumed on congested roads, the GAO stated.

A recent study on found that only about 17% of participants thought a new government sanctioned national speed limit would save fuel or improve safety. Most said 55 MPH was too slow or that law enforcement could better enforce current speed limits.

The GAO added that over the last 2 decades, fuel economy gains resulting from advances in automotive technologies have largely been offset by increases in vehicle weight, performance, and accessory loads. Specifically, vehicles are heavier than in the past, because they are larger and include more technologies. For example, average vehicle weight has increased from 3,220 pounds in 1987 to 4,117 in 2008, according to the Environmental Protection Agency.

In addition, trends show that recent vehicles, on average, have bigger, more powerful engines that yield better performance at the expense of fuel economy, the GAO stated. For example, according to the same EPA report, average horsepower has increased from 118 to 222 over the same period. Further, increased accessory loads, such as air conditioning and electronics, have also reduced fuel economy, the GAO said.

In looking back at the impact of the national speed limit, the estimated fuel savings resulting from the 55 MPH limit ranged from 0.2 to 3% of annual gasoline consumption.

According to the Department of Energy's 2008 estimate, a national speed limit of 55 mph could yield possible savings of 175,000 to 275,000 barrels of oil per day. According to the Energy Information Administration, total US consumption of petroleum for 2007 was about 21 million barrels of oil per day. In calculating these estimates, DOE assumed, among other things, a compliance rate of 50%.

Certainly all aspects of energy consumption are on the table as a new administration prepares to take hold in Washington, DC but one has too wonder if a national speed limit would be a priority in any form.

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