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March 11, 2014

Speed up: Limits could soon increase on DFW freeways

Speed limits on freeways across the Metroplex could go up 5 mph, if the Regional Transportation Council on Thursday reverses a 13-year-old policy of keeping limits low to reduce pollution.

North Texas drivers soon may be able to press the pedal a little closer to the metal.

Speed limits could be raised by 5 mph on many freeways across the Dallas-Fort Worth area by the 43-person planning group called the Regional Transportation Council at its regular meeting Thursday in Arlington. The move would reverse a 13-year-old policy of keeping speed limits low to reduce pollution from automobile emissions.

Regional planners have determined the low limits may no longer be necessary.

“The air quality benefit of traveling 60 or 65 mph now isn’t really as significant as it was in 2001,” said Jahnae Stout, spokeswoman for the North Central Texas Council of Governments. For decades, that agency has been instrumental in helping the region craft a plan to comply with increasingly tough federal pollution reduction laws.

If the measure is approved, signs with new speed limits could be installed on some Metroplex freeways once state and federal agencies sign off on the decision, a Texas Department of Transportation spokeswoman said.

The change would cover a lot of territory. For example, speed limits of 60 mph could be raised to 65 mph on Interstate 20, Loop 820 and Texas 121 in central Fort Worth, Grapevine, North Richland Hills and cities in or near the center of Tarrant County.

Speed limits of 65 mph could be raised to 70 mph on I-35W from Burleson to the south, and Alliance Airport to the north. Also, a 65 mph posted limit could be raised to 70 mph on U.S. 287 from I-35W north to Wise County, and from I-20 south through Mansfield.

The move wouldn’t affect highways where speed limits are already higher, outside the urbanized region of North Texas. For example, the speed limit on I-35 is already 75 mph for motorists traveling south of Johnson County toward Waco and Austin. Also, motorists on I-20 west of Weatherford toward Abilene, and east toward Shreveport, La., can already legally travel at 75 mph.

The threshold is even higher in the state’s most remote areas. I-10 and I-20 allow legal speeds of 80 mph between Monahans and El Paso in far West Texas. Between Austin and Seguin, motorists may travel 85 mph on the Central Texas Turnpike, assuming they’re willing to pay a toll.

The higher speed limits more accurately represent the pace at which traffic actually flows, and “more safely transitions the speed limits from the rural areas entering the Metroplex,” transportation department spokeswoman Jodi Hodges said.

Motorists have been asked to take it a bit easier in the state’s most populated areas since the early part of the last decade.

Research updated

In 2001, the Regional Transportation Council approved a plan to reduce speeds across the board by 5 mph, as Metroplex officials scrambled to find ways to meet EPA requirements.

The 5 mph cuts were included in a document submitted to the EPA by the state of Texas to show what steps would be taken to clean the air.

In recent months, the state transportation department — which owns and manages nearly 80,000 highway miles across the state — asked the North Central Texas Council of Governments to review the lower speed limits and see whether it would be feasible to reverse course.

Updated research by the council of governments shows that increasing speed limits by 5 mph could increase the emission of nitrogen oxides emitted into the air by roughly 0.4 tons a day. Nitrogen oxides, frequently referred to as NOx, are potentially harmful chemical compound produced by automobile engines powered by fossil fuels.

But the council of governments also identified several ongoing transportation improvements that would reduce traffic congestion and therefore reduce NOx emissions. Those include better traffic signal timing, the use of technology to warn motorists of bottlenecks and restrictions on trucks in the left lanes of many highways.

In preparing to raise the speed limits by 5 mph, Metroplex officials in recent months submitted to the EPA a list of things that could be done to offset any negative impact on air pollution, Stout said. The EPA approved use of offsets last month, clearing the way for the RTC to officially change the speed limits.

Back in 2001, computer modeling of automobile emissions suggested that when cars, pickups or heavy trucks surpassed 60 or 65 mph, emissions spiked. But more recent models that include the increased fuel efficiency of newer vehicles show the increase is not as dramatic as previously thought, said Chris Klaus, council of governments senior program manager.

“The faster emissions generally flat line at higher speeds for both cars and trucks now,” Klaus said.

But he said the new computer models show an increase in emissions when vehicles travel at speeds below 35 mph, a common problem during gridlocked periods, especially during weekday mornings and afternoons.

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