Purpose & Need


CDOT started the Westbound I-70 Peak Period Shoulder Lane (PPSL) project to respond to peak-hour traffic congestion on westbound I-70, similar to the improvements made through the Eastbound I-70 Peak Period Shoulder Lane project (now know as the I-70 Mountain Express Lane), which opened to traffic late in 2015.

The Westbound PPSL project connects the eastern logical terminus of the Veterans Memorial Tunnels—due to the slower speeds just west of that point—and the western logical terminus of Empire Junction—due to the high percentage of traffic that departs on US 40. It has independent use, and is a reasonable interim expenditure because it addresses safety, reliability and congestion related to geometry and grade. It addresses these purposes until CDOT can identify an ultimate solution in the study area.

The Westbound PPSL project is included in a January 2014 Memorandum of Understanding (MOU) signed by CDOT, Clear Creek County and the city of Idaho Springs. It is consistent with the non-infrastructure components (expanded use of existing transportation infrastructure) of the 2011 Record of Decision. It is an interim solution, not intended to address traffic problems 20 years in the future.

Purpose & Need

The purpose of these I-70 improvements is to provide westbound operational mobility improvements during peak periods when westbound traffic volumes are highest. Traffic congestion during peak periods erodes travel time reliability, increases traffic on local roads, decreases motorist safety and compromises the ability of emergency responders to respond quickly.

CDOT intends to quickly implement operational improvements on I-70, without substantial construction outside the existing highway footprint. The project is an interim solution for the study area, in advance of longer-term major improvements to the I-70 Mountain corridor in this area.

Project Needs

The interim project is needed due to rapid population growth in the Denver metropolitan area. In 2010, the population was 2,798,000 residents; by 2015, the metro area population had increased to 3,076,000—a 10 percent increase, or almost 300,000 people, in 5 years.

The existing section of westbound I-70 from the Veterans Memorial Tunnels to US 40 at Empire Junction has two westbound lanes. The westbound, outside shoulder is approximately 10 feet wide and the inside shoulder is approximately 4 feet wide. This stretch of I-70 is one of the most congested stretches of interstate in the entire mountain corridor.

Westbound I-70 has three specific transportation needs:

  • Travel time reliability. The current slow and unpredictable travel times on this stretch of I-70 severely affect I-70 mountain travelers, transportation-dependent commerce and other I-70 users.
  • Safety, including congestion-related crashes in this segment of I-70 and safety associated with rocks falling from the mountainside west of Idaho Springs onto I-70 travel lanes or shoulders.
  • Emergency service response is compromised in this section of I-70 because of the congestion
  • There are no pragmatic alternative routes between the Denver metro area and Colorado's central mountains. High traffic volume on I-70 during both summer and winter has led to ever-increasing periods of slow traffic, which at times is considered a gridlock situation. The predominant period for westbound I-70 congestion is on Friday afternoons and Saturday mornings, from the Denver metro area toward the mountains.

There is precedent in the study area for non-infrastructure improvements. In 2015, CDOT opened the I-70 Mountain Express Lane between Empire Junction and the Veterans Memorial Tunnels. Crews reconfigured the eastbound cross-section to provide a tolled travel lane on the inside shoulder during peak-period demand of heavy traffic returning to the metro area. This operational interim improvement project has notably alleviated eastbound congestion, reducing travel times by 21 minutes.

  • Travel Time Reliability
    I-70 recreational travelers, transportation dependent commerce, and other I-70 users are severely affected by the slow and unpredictable travel times on this stretch of I‑70. This travel time reliability issue affects tourism and economic development.
    • During non-peak periods, in uncongested free-flow conditions—from the Veterans Memorial Tunnels to Empire Junction—travel time is 12 minutes. In contrast, travel time during peak periods ranges from 16 minutes to 21 minutes—increases of 33 percent to 75 percent. Travel time during the peak period for 2035 is forecast to be just over 22 minutes (see image below).

    • Congestion persists on the I-70 Mountain corridor outside the study area. The study area is a reasonable and suitable segment of I-70 for interim operational improvements.
  • Local Access
    Some motorists divert to alternate routes (primarily frontage roads), causing congestion for local traffic and reduced safety on these roads. The frontage road is the "main street" for Downieville, Lawson and Dumont, and the only continuous east-west local street in Idaho Springs.
    • Weekday two-way traffic counts on the Stanley Road frontage road average 900 vehicles per day, but the volume more than doubles on weekend days. When I-70 travelers use the frontage road to avoid congestion on the highway, area residents and businesses are inconvenienced because they cannot get out of their driveways onto the frontage road. In addition, in-town roads in Idaho Springs are congested because travelers cut through town to avoid I-70 congestion.
  • Safety
    Congestion-related crashes occur on I-70. Analysis of crash data in this stretch of I‑70 shows that there is a cluster of concrete barrier crashes on westbound I-70 around exit 240, and just east of Exit 241; a cluster of rear-end crashes near the Veterans Memorial Tunnels; and a high concentration of wildlife-vehicle collisions along the US 40 off- and on-ramps. (Source: 2017 Safety Assessment Report, Felsburg, Holt & Ullevig)

    • Emergency service responders working in the study area are delayed by the congestion and lack of alternate ways to get to incidents on I-70. The current edge-to-edge pavement is narrow and emergency vehicles have difficulty maneuvering through the density of congested vehicles to access incidents during peak periods.

      The severe congestion affects speed of response to incidents on I-70, incidents in adjacent communities and incidents affecting recreationists using the Clear Creek corridor. The resulting delay in effective incident management compromises safety and substantially inconveniences other travelers.

    • Travelers' safety is also compromised by rocks falling onto I-70, due to its proximity to steep mountain slopes. (See more information about rockfall issues below.)
  • Transit
    There is a lack of safe and efficient facilities for regional transit passengers on the Bustang route, which serves the I-70 Mountain corridor between Glenwood Springs and the Denver metro area. This is also an issue with the county-run Prospector bus. Passengers have high exposure at current stops in Idaho Springs on Miner Street, and they provide no amenities to passengers. Further, both eastbound and westbound buses must make inefficient turnarounds to return to I-70, causing increased travel time to all regional passengers.
  • Deficient Infrastructure
    The current highway is deficient in many aspects, including substandard and failing facilities for drainage, guardrails, and pavement.
    • Current traffic levels far exceed original plans, designed in the 1950s. Some ramps have inadequate sight distance, and deficient design of  acceleration and deceleration lanes.
  • Rockfall Hazards
    Westbound motorists are adjacent to unstable rocks west of Idaho Springs in the study area, which affects safety and mobility. Between 2014 and 2017 (as of October 2017), there have been 49 rockfalls that have affected the entire interstate, westbound I-70 lanes or shoulders. These events closed lanes for as few as 30 minutes to as long as several days.

These project need elements formed the framework for developing the project, which was assessed in the Westbound PPSL Categorical Exclusion (National Environmental Policy Act document).

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The I-70 Mountain corridor is a magnificent, scenic place in close proximity to the Denver Metro area. Human elements are woven through breathtaking natural features. The integration of these diverse elements has occurred over the course of time. The corridor is a recreational destination for the world, a route for interstate and local commerce and a unique place to live.

I-70 is also federally designated as a high-priority corridor, a significant part of the defense network, a major east/west continental corridor and a major economic corridor for Colorado. For many local communities along the corridor, I-70 is the lifeline, primary access and only connection to other communities.

Current I-70 roadway geometry is constrained with narrow shoulders and tight curves that impact safety, mobility, accessibility, and capacity for travelers and residents. In a manner that respects the unique environmental, historic, community and recreational resources in Clear Creek County, westbound improvements are needed to lessen delays caused by peak period volumes.


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