The History of I-70 in Colorado
The Federal Highway Act of 1944 initially authorized Interstate 70 between Denver and the Kansas state line. As part of this act, there was no interstate mileage allotted west from Denver but this omission would be dealt with under the 1956 Interstate Act.
Initially, Colorado would not be able to build I-70 west of Denver since the state of Utah was not interested in a connecting interstate route through eastern Utah since the route it would follow – U.S. 6 & 50 – had mountainous terrain, which would mean it would be very costly to build an interstate route. However, officials with the Colorado Department of Highways were determined to have I-70 continue west of Denver . After much negotiation with Utah officials, Utah approved such a route and Congress approved the additional mileage of I-70 from Denver west to U.S. 91 (to become I-15) in south-central Utah in October, 1956.