DNT 4th Lane Widening and Capacity Improvements, NTTA
Collin County, TX

Part of an overall improvement plan to provide a better driving experience for customers along the DNT from IH 635 to Sam Rayburn Tollway, this 2.71-mile project extended from south of Parker Road to south of Sam Rayburn Tollway.

The project primarily involved the addition of a fourth lane to the main lanes in each direction. This widening required realignment of 14 ramps, relocation of 6 toll gantries, 6 bridge widenings, one bridge replacement, drainage improvement, ITS improvements, and extensive addition, modification, or replacement of the retaining walls along the corridor.


IEA provided traffic control plans (TCP) and construction phasing for the Tennyson Bridge section of this project. IEA provided two TCP concepts to the City of Plano and NTTA for consideration. The City of Plano opted for IEA’s multi-phase design to keep the bridge open for citizens to travel. The advantage of allowing the bridge to remain open includes allowing the traffic to flow without interruption. The DART bus system would not be affected with lost travel time or bus stops. Public frustrations would be minimal, with less travel time lost and keeping routes uninterrupted.


IEA provided roadway designs for this project.

  • U-turn and frontage road profiles
  • Grading limits
  • Sheet set-up
  • Reduced frontage footprint


IEA designed the replacement of the existing 120’ long, 169’ wide single span precast prestressed concrete bridge at Tennyson Parkway with a 160’ long, 172’ wide single span steel girder bridge with an additional 27’ width at the flares. IEA designed the structure to be built in two phases, using drilled shaft foundations that also serve as the retaining wall support. The single span, staging of the structure, traffic control, and use of a combined drilled shaft/retaining wall minimized impact to the customer during construction.


IEA provided utility coordination with Oncor Electric and Verizon. IEA placed existing plan view utility locations for the Tennyson/DNT intersection. IEA coordinated with the utility companies early to avoid any delays in the schedule due to coordination with an outside agency. IEA discussed existing and future crossings, received the utility design standards, and discussed comments of the utility companies. Interdisciplinary coordination required a utility design realignment to better fit the girder layouts.


IEA provided professional services for ITS plans preparation that include CCTV and DMS placements and approximately 4 miles of conduit. IEA was responsible for existing gantry removal plans and site plans for 6 new gantry locations. In keeping project goals, IEA also developed plans for temporary toll facilities, minimizing impacts to tolling operations.


Collin County, TX

Services Provided

Widening and Capacity Improvements