The I-25 South Gap is an 18 mile stretch of Interstate 25 from south of Castle Rock to Monument. It is the only four lane section of the highway connecting Colorado’s two largest cities, Denver and Colorado Springs. Congestion, accidents and delays have grown significantly. With forecast growth in the area, these issues are forecast to worsen. Ch2MHill and team members, including ArLand, were selected to help CDOT conduct an environmental assessment of potential alternatives within record time.