Monday, October 13, 2008

Newest segment of 121 Tollway between Carrollton and Plano/Frisco line has 70-mph speed limit

By Pegasus News wire

CARROLLTON — The North Texas Tollway Authority would like to inform motorists that the main lanes on the newest segment of the 121 Tollway -- also known as "segment two" -- have a 70-mph speed limit, even though there are no speed limit signs currently posted.

Under Texas law, 70 mph is the "prima facie speed limit" - in other words, the presumed safe maximum speed on the road until a speed limit is specifically determined. It will remain in effect until the completion of a speed study by the Texas Department of Transportation.

The 121 Tollway officially transferred to the NTTA System from TxDOT on Sept. 1, 2008. According to the project agreement, TxDOT is required to conduct a speed study on the frontage roads and main lanes of the 121 Tollway's newest segment, also known as segment two, between six to eight weeks after the service commencement date to allow time for traffic patterns to stabilize.

Segment two opened Aug. 31 and extends from Old Denton Road in Carrollton to Hillcrest Road on the Plano/Frisco line. Segment one, which opened in the summer of 2006, extends from Denton Tap Road in Coppell to Old Denton Road in Carrollton. Segment one currently has a 70-mph speed limit, which was previously determined and posted by TxDOT.

The 121 Tollway has three additional segments to be constructed. Upon their completion, speed limits will be similarly determined and implemented for each of those segments.

The speed study for segment two should be complete by the end of the year. It will measure the speeds of free-flowing vehicles during weekday off-peak hours under favorable weather conditions. The speed checks are conducted for a maximum of 125 vehicles at each location or for a two-hour period, whichever comes first.

Once the free-flowing speeds are collected at each check point, they are compiled to calculate the 85th percentile speed-the most characteristic representation of traffic speeds that are safe and reasonable.

The NTTA also considers special unique features of the roadway when making a final recommendation. Once complete, the recommended speed limits will become legal pending resolution approval by the NTTA Board of Directors.

Source: NTTA

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