westbound I-70 reenters Denver, and the eastbound I-70 to southbound I-225 ramp originates in Denver but enters Aurora as it passes under westbound I-70 to southbound I-225 ramp. Like other state highways in Colorado, I-225 is maintained by the Colorado Department of Transportation (CDOT), an agency who is responsible for maintaining and constructing transportation infrastructure across Colorado. In 2014, the department's traffic surveys showed that I-225 serves approximately 71,500 vehicles per day between I-25 and Parker Road and 60,750 vehicles north of Parker Road going in and out of Aurora. All of I-225 is part of the National Highway System (NHS), a network of roads important to the country's economy, defense, and mobility. History I-225 was originally proposed by CDOT to be numbered as I-25E on April 3, 1958, based upon the Route Numbering Committee signing north, south, east, and west routes as suffixed routes in the Interstate Highway System. AASHTO rejected the designation, and the highway was then assigned the I-225 designation following further correspondence the following year. Construction and expansion Construction on I-225 began in May 1964 at I-70. A section from Colfax Avenue to Sixth Avenue was opened in 1966. The first segment of freeway that ran from sixth Avenue to I-70 received a temporary carrier route that was cosigning I-225 as State Highway 33. CDOT then removed the state highway designation in 1968 as part of an effort to remove carrier routes on existing US and Interstate highways. Five years later, a segment between Mississippi Avenue and Parker Road was opened, and construction began on another segment south of Parker Road, completed in May 1975. The rest of the route between Yosemite Street and I-25 was completed in May 1976. Immediately after the completion of the freeway, improvements at the SH 30 (6th Avenue) interchange were underway involving the overpass. Reconstruction of the freeway between 30th Avenue and Smith Road took place between October 1992 to August 1994, which involved bridge replacements over Toll Gate Creek and Smith Road that were completed by August 1990 in an effort for the reconstruction project. Two months after the reconstruction project, the I-70/I-225 interchange reconstruction went underway, which involved widening I-225 from I-70 to Smith Road and improvements to the flyover ramps at the interchange that was completed in April 1995. From February 1996 to November 1997, I-225 was expanded to six lanes between Toll Gate Creek and Colfax