I-25 South Gap: Monument to Castle Rock

Project complete

About the Project

The Colorado Department of Transportation and contractor partner, Kraemer North America, completed construction on the 18-mile I-25 South Gap project in November 2022.

Construction Overview

The I-25 South Gap work zone stretched 18 miles between Monument and Castle Rock. The project was split into three geographic regions:

  • North: Castle Rock to Sky View Lane (Tomah Road)
  • Middle: Sky View Lane (Tomah Road) to Greenland Road
  • South: Greenland Road to Monument

Splitting up the project allowed construction to begin on one section, while design was finalized on another. Scroll down to learn the construction elements in each section.

North: Castle Rock to Sky View Lane (Tomah Road)

  • This section received an Express Lane, wider shoulders and new pavement in both directions.

South: Greenland Road to Monument

Here’s what to expect from construction between Monument and Greenland Road:

  • Monument to County Line Road: Construction included widening, earthwork, asphalt paving, storm sewer pipes, a new wildlife crossing, median barrier and retaining walls. 
  • County Line Road to Greenland Road: Construction included a new wildlife crossing, widening, storm sewer pipes, median barrier and retaining walls. In 2019, CDOT added funding to replace the County Line Road bridge.
  • Greenland Road: The Greenland Road interchange was completely rebuilt from a single lane box culvert, which was originally built in 1948, to a two lane underpass. Construction in this area also included a new wildlife crossing.
  • Monument Hill Frontage Road: Construction of a new wildlife crossing.
  • County Line Road bridge: Reconstruction of the County Line Road bridge. The bridge doubled in size to accommodate one through-lane in each direction, a turn-lane in each direction and wider shoulders.  

Middle: Tomah Road to Greenland Road

  • This 6-mile section was the most complex. Construction included new Express Lanes, wider shoulders, a new wildlife underpass and bridge replacements at Upper Lake Gulch Road, Spruce Mountain Road and Plum Creek.

Project Facts

The Gap is an 18-mile stretch of Interstate 25 from south of Castle Rock to Monument. It is the only four-lane section of I-25, connecting Colorado's two largest cities, Denver and Colorado Springs. Over the years, congestion, crashes and delays have grown due to population growth and more people using the road.

Efforts to improve these conditions are underway.

  • Cost: $419 million, with contributions from Douglas and El Paso counties, Pikes Peak Rural Transportation Authority and a federal INFRA grant (scroll down for details)
  • Contractor: Kraemer North America
  • Timeline:  Construction began in September 2018 and completed in November 2022
  • Location: 18 miles in both directions of I-25, south of Castle Rock to Monument, in Douglas and El Paso counties

Project Benefits

The I-25 South Gap: Monument to Castle Rock project delivered:

 Increased Safety: Wider shoulders allow room for vehicle pull-off and emergency response. This improvement also helps with drainage.

 Driver choice: The addition of an Express Lane in each direction of I-25 gives motorists the choice to use the Express Lane for a reliable trip in exchange for a toll or to use one of the two general-purpose lanes for free. Carpoolers (vehicles with three or more people) and motorcyclists can ride the Express Lanes for free.

 Wildlife safety: Four new wildlife crossings and 28 miles of deer fencing are anticipated to help decrease animal-vehicle collisions by 90 percent.

 Improved pavement: A new asphalt overlay to the existing pavement provides a smoother ride.

 Improved infrastructure: Reconstruction of five aging bridges and the extension of on- and off-ramps for improved operations.

 Improved truck access and safety: Implementation of truck climbing lanes near Monument Hill and the Greenland exit allow slower moving vehicles to stay to the right. A new truck chain-up station along southbound I-25 in Larkspur allows drivers to safely chain up in inclement weather before the climb over Monument Hill.

 Advanced technology: Modernization of communications and power along the corridor to enable advanced technology.

Tolling Information

Tolling on these lanes began in 2024. Visit I-25 South Gap Express Lanes for more information.


Study Projects Lowest Tolls in State for I-25 South Gap Express Lanes

Project Schedule

Construction Begins in Phases, Starting on North End

The 18-mile I-25 South Gap project is split into three geographic sections – north, middle and south.

North Section: Castle Rock to Tomah Road
Since construction began in September 2018, roadwork focused on the northern section of the project, between Plum Creek Parkway and Sky View Lane/Tomah Road. Traffic was shifted to the outside to build the new Express Lanes in the center median. Next, crews will shift traffic to the center median so construction can occur on the outside. Overnight single lane closures will continue in this area. Watch for trucks entering and exiting the work zone.

South Section: Greenland Road south to Monument
In early 2019, construction will begin in the southern section of the project between Greenland Road and Monument. This section is more complex. Overnight lane closures and extended closures of the Greenland Road and County Line Road ramps and Monument Hill Road will be required for safety-critical work. Please be prepared for frequent changes in traffic patterns and reduced shoulder and lane widths. The speed limit will be reduced in this area as well.

Middle Section: Greenland Road to Sky View Lane
This section is the most complex. Work here is expected to begin in summer 2019.

Remember: All construction schedules in Colorado can be impacted by weather.

North Section Traffic Shifts

During construction on the northern end of the project—between Plum Creek Parkway and Sky View Lane—crews will shift traffic three times:

  • Traffic Shift No. 1
    • Crews have already shifted traffic to the outside shoulders to work on the I-25 median, where the new Express Lanes and wider shoulders will be built.
  • Traffic Shift No. 2
    • Then, traffic will move to the newly constructed area, so crews can work on the outside lanes. 
  • Traffic Shift No. 3
    • Finally, traffic will move back to the outside, so crews can place the final overlay and striping.