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New I-66 technology helping some drivers, but not daily commuters

Monday's morning commute may not be the best measure of how Metro's track work will impact area traffic. (WTOP/Dave Dildine)

FAIRFAX, Va. – A high-tech traffic control system is speeding up cars along Interstate 66, but not during the traditional rush hour.

The Active Traffic Management system complete with overhead variable speed limit signs and lane control signs launched in mid-September. New data from the Virginia Transportation Research Council, the research arm of the state’s Department of Transportation, show that drivers traveling in the opposite direction of rush hour traffic on I-66, or traveling in the middle of the day or on weekends, are moving faster than they did at the same time a year ago. Traffic traveling in the traditional rush-hour direction, however, has continued to worsen.

Researcher Michael Fontaine said the differences are likely largely explained by the fact that the shoulder lanes are now opened to traffic outside of the typical rush hour, based on traffic congestion. The shoulder lanes were already available to rush-hour traffic — eastbound in the morning and westbound in the evening.

The algorithm behind the system had problems when it first rolled out and is still being tweaked. But preliminary data indicate the system may be contributing to a reduction in crashes.

“Ideally, the speed limit signs are first of all providing an advance warning that traffic is stopped ahead. Some of the most severe crashes we have are when people are going very fast running into the end of a stopped queue,” Fontaine said.

Transportation officials hope that the traffic control technology also encourages drivers to maintain consistent speeds to help traffic flow more smoothly.

Fontaine notes that the variable speed limit signs are actually enforceable by police, and are not just recommendations.

Because this is one of the first systems of its kind in the United States, researchers are watching closely to see how drivers react to it. In Europe, similar systems are often coupled with speed cameras to enforce the variable speed limits and encourage drivers to maintain a smooth flow; however, that is not planned for the I-66 corridor.

Fontaine also says there are no plans to display different speed limits in each lane because of the risk that the differences in speed could contribute to a crash if a driver decided to change lanes.

State researchers looked at travel times between the Centreville exit and the Capital Beltway to determine the impact of the new signage and changes to the use of the shoulder lanes.

Average Eastbound Weekday Travel Times

Time Period Oct 2014 – Feb 2015 Oct 2015 – Feb 2016 % Change
AM Peak (5:30AM – 11AM) 17.0 min 18.2 min 7 percent
Midday (11AM – 2PM) 13.3 min 13.2 min -1 percent
PM Peak (2PM – 8PM) 14.7 min 13.7 min -6 percent

Average Westbound Weekday Travel Times

Time Period Oct 2014 – Feb 2015 Oct 2015 – Feb 2016 % Change
AM Peak (5:30AM – 11AM) 12.6 min 12.3 min -2 percent
Midday (11AM – 2PM) 13.3 min 12.7 min -5 percent
PM Peak (2PM – 8PM) 21.7 min 22.5 min 4 percent

Average Weekend Travel Times

Time Period & Direction Oct 2014 – Feb 2015 Oct 2015 – Feb 2016 % Change
Eastbound (10AM – 8PM) 14.5 min 13.1 min -10 percent
Westbound (10AM – 8 PM) 13.7 min 12.2 min -11 percent

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