Traffic control technology implemented in Northern Virginia encourages drivers to maintain consistent speeds to help traffic flow moresmoothly.
Fairfax County, Virginia, United States
New I-66 technology helping some drivers, but not daily commuters.
Summary Information
In September 2015, the Virginia Department of Transportation (VDOT) activated an active traffic management (ATM) system on I-66 through Arlington, Fairfax and Prince William counties from the Washington, D.C. line to Route 29 in Gainesville. The system includes new overhead sign gantries, shoulder and lane control signs, speed displays, incident and queue detection, and increased traffic camera coverage. A total of 21 overhead gantries were installed in each direction between the Beltway and Route 29 in Centreville and were spaced .6 miles apart.
Methodology
State researchers looked at travel times between the Centreville exit and the Capital Beltway (approximately 12.5 miles) to determine the impact of the new signage and changes to the use of the shoulder lanes. Data were analyzed for October 2014 to February 2015 (Before-ATM) and from October 2015 to February 2016 (After-ATM).
Findings
Hard Should Running Utilization in Hours (Average hours of operations/ day per Gantry)
| Direction - Average Day | Before ATM | After ATM |
| Eastbound - Weekday | 5.5 | 8 |
| Eastbound - Weekend | N/A | 2.4 |
| Westbound - Weekday | 6 | 6 |
| Westbound - Weekend | N/A | 2 |
Avg EB Weekday Travel Times
| Time Period | Oct 2014 - Feb 2015 | Oct 2015 - Feb 2016 | Change |
| AM Peak (5:30 AM - 11 AM) |
17.0 min | 18.2 min | +1.2 (+7%) |
| Midday (11 AM - 2 PM) |
13.3 min | 13.2 min | -0.1 (-1%) |
| PM Peak (2 PM - 8 PM) |
14.7 min | 13.7 min | -1.0 (-6%) |
Avg EB Weekend Travel Times
| Time Period | Oct 2014 - Feb 2015 | Oct 2015 - Feb 2016 | Change |
| Daytime Peak (10 AM - 8 PM) |
14.5 min | 13.1 min | -1.4 (-10%) |
Avg WB Weekday Travel Times
| Time Period | Oct 2014 - Feb 2015 | Oct 2015 - Feb 2016 | Change |
| AM Peak (5:30 AM - 11 AM) |
12.6 min | 12.3 min | -0.3 (-2%) |
| Midday (11 AM - 2 PM) |
13.3 min | 12.7 min | -0.6 (-5%) |
| PM Peak (2 PM - 8 PM) |
21.7 min | 22.5 min | +0.8 (+4%) |
Avg WB Weekend Travel Times
| Time Period | Oct 2014 - Feb 2015 | Oct 2015 - Feb 2016 | Change |
| Daytime Peak (10 AM - 8 PM) |
13.7 min | 12.2 min | -1.5 (-11%) |
Total Traveler Delay (veh-hour)
| Direction | Average Day | Before ATM | After ATM | Change |
| Eastbound | Weekday | 2968.5 | 3353.4 | +13.0 % |
| Eastbound | Weekend | 1682.5 | 704.7 | -58.1 % |
| Westbound | Weekday | 5121.6 | 5583.3 | +9.0 % |
| Westbound | Weekend | 1292.5 | 416.8 | -67.8 % |
Conclusions
- The ATM system had minimal effect on travel times during weekday peak periods, since shoulders were already in use before installation.
- Small benefits were observed in the off peak direction and during midday periods during the week.
- Flow improved substantially during the weekends. Both mean travel time and travel time reliability improved by a statistically significant amount.
- Most operational improvements appear to be attributable to shoulder lane usage.
- Preliminary safety data is promising, but more data is needed.
