Frequently Asked Questions


The purpose of the Westbound Peak-Period Shoulder Lane (PPSL) project is to provide westbound operational improvements during peak periods when 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.

Similar to the Eastbound PPSL project (now called the I-70 Mountain Express Lane)—which was implemented in 2015—the Westbound PPSL will use the existing shoulder as a tolled, third travel lane only during peak travel times on the 12 miles of westbound I-70 between the Veterans Memorial Tunnels and Empire Junction. The Westbound PPSL is not the permanent solution for the corridor; it's an interim, operational improvement to help ease congestion until a permanent solution can be developed and implemented.

In June 2011, the Federal Highway Administration (FHWA) issued a Record of Decision (ROD) outlining a number of actions to address I-70 Mountain Corridor congestion, and provide a path forward to improving mobility along the corridor.

One of the categories for improving mobility is "Non-Infrastructure Related Components—Expanded use of existing transportation infrastructure in and adjacent to the Corridor." The Westbound PPSL project fits within that category.

Learn more.

A Tier 1 National Environmental Policy Act (NEPA) process was completed in 2011 for the 1-70 Mountain Corridor from C-470 in Golden to Glenwood Springs. Tier 1 NEPA processes focus on strategies for an entire corridor to make broad policy decisions. The I-70 Mountain Corridor Tier 1 NEPA process made decisions on general location, mode and capacity.

A Tier 1 record of decision (ROD) was approved for the I-70 Mountain Corridor. It provided a long-term vision for the 144-mile corridor that includes a program of transit, highway, safety and other improvements to increase capacity, improve accessibility and mobility, and decrease congestion. This decision provided a framework for implementation of specific projects, which are then evaluated through Tier 2 NEPA processes.

Tier 2 NEPA processes can then focus on analyzing project-specific impacts and issues because the broad decisions are made at the Tier 1 level. The Westbound PPSL project was evaluated through a Tier 2 NEPA process.

The purpose of tolling the PPSL is to manage congestion and provide travel-time reliability. The purpose of tolling is not to pay for this construction or to generate revenue for CDOT. The High Performance Transportation Enterprise (HPTE; an entity within CDOT that operates as a government-owned business and focuses on financing) operates the PPSL rather than a private operator. The two existing lanes remain free to all travelers and travelers who choose not to pay the toll will also realize congestion relief. The new PPSL tolls single-occupant and multi-occupant vehicles. Buses and commercial vehicles of more than two axles are prohibited from using the lane.

CDOT has used similar lanes for over a decade as a proven way to enhance travel-time reliability and increase corridor throughput. The PPSL also provides opportunities to leverage emerging technology, and allow flexibility to adapt highway operations to changing travel patterns and technologies.

The I-70 Mountain Corridor record of decision (ROD) specifically encourages improvements that adapt to changes in global, regional or local trends that have unexpected effects on travel needs, behaviors and patterns.

The Westbound PPSL project is expected to see similar benefits to mobility and throughput as the I-70 Mountain Express Lane. For that Express Lane, travel times improved overall by 21 or 22 minutes,to 52 percent. This included all lanes of travel (including the existing free lanes), which means it benefits all users of the interstate whether a toll is paid. In addition, incident clearance times were 17 minutes faster, and there is less congestion on the free frontage road.

The tolls are used to pay back the loan for the project, and to pay for subsequent operations and maintenance.

Drivers are not required to use the PPSL, which is tolled. If a driver doesn't use the PPSL, that driver doesn't pay a toll. Drivers always have the option to use the two existing general-purpose lanes for free.

All users of westbound I-70 realize safety and travel benefits, such as reduced crashes associated with congestion, reduced congestion, improved travel times and improved incident management. Drivers whose taxes contribute to funding the Westbound PPSL project and who choose to use the PPSL pay a toll that benefits travel-time reliability.

With 70 percent of the project funding coming from state sources, taxpayers across Colorado are paying for the project.

The initial toll rates were established from a traffic model of the I-70 Mountain Corridor that considered traffic congestion and value of time. These base rates are set up for time-of-day tolling.

The CDOT I-70 Mountain Corridor manager can extend the tolling period earlier or later, if congestion persists. They can also adjust the toll rates during the day based on observed volumes and congestion. Thus far, toll rate adjustments for eastbound I-70 have happened infrequently because the lane has been operating well (i.e., providing a reliable travel time). The current base toll rates are $5 on Saturday and $6 on Sunday. Tolls are expected to be set similarly for the Westbound PPSL.

The peak periods on westbound I-70 are Friday afternoons, and Saturday and Sunday mornings during peak summer and winter travel seasons, as well as holiday mornings. Therefore, the Westbound PPSL is likely to be open to traffic on Friday afternoons, and in the mornings on Saturdays, Sundays and weekday holidays. Exact hours of operation have not yet been determined.

Operations will be flexible and available for use beyond those days or times if traffic congestion conditions warrant, so long as the operating hours stay within the daily and annual guidelines established by a Memorandum of Understanding (MOU) that will be signed by the FHWA, HPTE, and CDOT.

Because the Eastbound and Westbound PPSLs are considered interim projects that are operational improvements for peak periods, FHWA, HPTE, and CDOT signed Memoranda of Understanding that define the maximum yearly times of operations. The agreement for the Eastbound PPSL is that it can be open no more than 100 days of the year and no more than 1,168 hours per year. The agreement for the Westbound PPSL is that it can be open no more than 125 days of the year and no more than 965 hours per year.

Rather than widen the highway, the Mountain Express Lane uses existing infrastructure to address peak period congestion in the interim until additional capacity can be added. Full-width shoulders and lanes were considered but not implemented because of cost, environmental impacts, and inconsistency with the 2011 record of decision (ROD), which did not identify this area as one to be widened for additional highway capacity until certain triggers are met. These triggers have not yet been met and can be found in the 2011 Record of Decision.

As an interim, operational improvement, the temporary nature of the project enables the use of "less-than-ideal" widths for lanes and shoulders. CDOT and FHWA are working through the I-70 Mountain Corridor Context Sensitive Solutions (CSS) process with local agencies and other stakeholders to determine the appropriate shoulder and lane widths for the Westbound PPSL project. FHWA determines if any variances to normal interstate standards are acceptable.

The accident history of the I-70 Mountain Express Lane shows that in the first year of operation, there were more crashes than prior to its implementation. During the second year of operation, the number of crashes decreased when compared to crashes reported before its implementation.

However, based on public input and input during the CSS process, the proposed width of the Westbound PPSL is wider than the I-70 Mountain Express Lane by two feet. This allows one extra foot in the inside general-purpose lane, and one extra foot between the PPSL and the median.

CDOT is planning to construct a new bridge over Clear Creek from Stanley Road to the Fall River Road interchange, but it will not be a part of the Westbound PPSL project. The bridge project is planned to begin before construction of the Westbound PPSL project.

Clear Creek Greenway

Several sections of the Clear Creek Greenway are planned to be funded by CDOT as a part of a separate project. CDOT, Clear Creek County, the Clear Creek Greenway Authority, and Idaho Springs are working together to determine which sections will be built. Once more information is known, a community meeting will be held.

If you have further questions about the Clear Creek Greenway, please contact Amy Saxton with the Clear Creek Greenway Authority at 720-588-9443.


Except in limited circumstances (e.g., adverse weather, construction zones), per 23 CFR 658.11(d), the state of Colorado cannot deny truck access, nor place restrictions on the interstate system without FHWA approval.

The request needs to be based on safety concerns. It requires an analysis of the impact to interstate commerce, and analysis and recommendations of alternative routes.

Motor carriers groups are involved in the Westbound PPSL project. CDOT is working with these groups to consider impacts to truck traffic movements both during construction and after the Westbound PPSL is in operation.

CDOT is not considering tolling all lanes on I-70. There will be two free lanes just like there are now. However, if local residents choose to travel in the PPSL, they will have to pay a toll.

During construction, there will be a robust public information plan to notify travelers, residents, and businesses of closures and detours through a variety of methods. In addition, CDOT has upgraded its intelligent highway systems along I-70 to help better respond to these needs.

These upgraded systems will better inform users of road conditions in the future. CDOT is continuing to develop improvements in traffic management and intelligent systems.

Speed limits will be posted for the Westbound PPSL. Because the Colorado State Patrol (CSP) is responsible for enforcing speed limits, CDOT will discuss implementing more frequent enforcement of speed limits with the CSP. Five pull-outs are being included as a part of the Westbound PPSL project, and two new pull-outs are being added on the eastbound side to allow more opportunities for enforcement.

Construction Impacts

One of CDOT's key concerns is to minimize impacts as much as possible to the traveling public. The Veterans Memorial Tunnels and I-70 Mountain Express Lane projects did disrupt traffic during construction, but there is no indication that travelers chose to never come back. Trying to minimize the disruption to travelers and communities during construction is one of the main goals of CDOT projects.

Air quality impacts during construction were considered during the NEPA process and best management practices will be included during construction. Best management practices include items such as keeping construction equipment well-maintained, using the cleanest fuels available in construction equipment and vehicles, and preparing a Fugitive Dust Control Plan that specifies practices to reduce dust during construction.

Detours during construction will be formalized once a contractor is selected. One of CDOT's goals is to minimize short-term impacts to traffic as much as possible. The short-term effects to truck traffic and Henderson Mine operations will likely be similar to those experienced during construction of the I-70 Mountain Express Lane.

Dumont-Lawson-Downieville Noise Issue

The Westbound PPSL project is an interim project and does not meet the definition of the type of project that requires a noise analysis. Based on information collected after the I-70 Mountain Express Lane was operational, adding a part-time tolled lane does not perceptibly change noise levels.

However, the concrete barrier with glare screen in Lawson that was installed along with the I-70 Mountain Express Lane provides noticeable incidental noise reduction benefits to the adjacent areas. The Westbound PPSL project also includes concrete barriers with glare screens, which are also anticipated to provide noticeable incidental noise reduction benefits to the adjacent areas.

Colorado state law now requires that any vehicle equipped with engine-compression-brake devices (commonly referred to as "Jake brakes") be equipped with proper mufflers. Failure to do so results in a $500 fine. The enforcement of this law is the responsibility of the local authorities.

CDOT has not restricted the use of these devices for safety reasons. However, CDOT has assisted local entities with this issue by installing "Engine Brake Mufflers Required" signs along selected highways, which could also be considered for this area.

Environmental/Socioeconomic Resources

The Westbound PPSL project development process included consideration of wildlife mitigation to better facilitate their movement across I-70. A specific committee called ALIVE (A Landscape Level Inventory of Valued Ecosystem Components) addresses wildlife needs and recommended mitigation for wildlife. Due to the interim nature of the project, large wildlife passages will not be included in the project. However, signage will be posted in key bighorn sheep areas to alert drivers to the potential for wildlife on or near the road, small mammal openings will be provided in the median barrier to allow movement across the highway, and some fencing will be removed near an underpass in east Idaho Springs to facilitate movement at that location.

Air quality was considered as a part of the National Environmental Policy Act (NEPA) process. Decreasing traffic congestion with the Westbound PPSL can be expected to reduce air pollution from vehicles. Best management practices are being incorporated for temporary impacts associated with construction.

Water quality was considered as part of the National Environmental Policy Act (NEPA) process. A specific committee called SWEEP (Stream and Wetland Ecological Enhancement Program) is tasked with developing water-quality treatment plans. A Sediment Control Action Plan has also been prepared that defines treatment for excess sediment along I-70. Its recommendations were considered in the NEPA process. Three detention ponds will be incorporated as part of the project as well as multiple drainage improvements at existing ponds, ditches, and inlets throughout the project.

The frequency of CDOT Bustang service on I-70 between Glenwood Springs and the Denver area has been increased, and it is likely to be further increase as needs grow and if funding is available. Outreach to providers of shared ride services was conducted as part of the NEPA process.

Aesthetics are an important part of any project that CDOT studies. All projects on the I-70 Mountain Corridor must comply with the Design Criteria and Aesthetic Guidance that was developed specifically for the corridor.

The Westbound PPSL project includes moving a portion of the existing noise wall approximately 3 to 4 feet behind its existing location. It will provide the same noise abatement as the existing noise wall.

Parking is impacted by the improvements to the Colorado Highway 103 interchange as part of the Westbound PPSL project. However, the current parking lot will be reconfigured so that no spaces are lost. During construction, parking capacity will be reduced. The city of Idaho Springs is also planning to build a parking garage in the future.

The Westbound PPSL project is anticipated to stay within CDOT's existing right-of-way; therefore, property will not be acquired and no houses will be impacted anywhere within the corridor.


The I-70 Mountain Express Lane resulted in overall improved economic conditions by easing peak-period congestion. Upgrades to the CO 103 and Exit 241 interchanges made businesses directly adjacent to the interchanges easier to access from I-70, as well as providing increased safety for residents, businesses and emergency service providers.

The I-70 Mountain Express Lane also reduced congestion-related traffic on I-70 during peak periods and improved emergency response times because emergency service providers are able to use the MEXL during off-peak periods for emergencies. The lane is less congested during peak hours, allowing emergency services to respond faster.

Easing of congestion during peak periods encourages more recreation- and tourism-oriented trips to Clear Creek County and other counties to the west. This indirect effect benefits local businesses from an increase in visitation to the area, is positive for economic conditions, and is of particular interest to Clear Creek County, which is actively encouraging a shift in the economic base to businesses that are more tourist-oriented.

The findings relative to the benefit provided for the cost of improvements for the I-70 Mountain Express Lane is that it was very cost-effective ("I-70 Eastbound Peak Period Shoulder Lane TIGER Application, CDOT April 2014"; "I-70 Westbound Peak Period Shoulder Lane INFRA grant application, CDOT November 2017").

The I-70 Mountain Express Lane substantially saved travel time and substantially improved time to clear crashes, at a cost that is much less than the cost to build a new, full-time lane. The Westbound PPSL is anticipated to provide similar benefits for relatively low cost.

In 2014, a feasibility study was completed for an Advanced Guideway System (high-speed public transit) and it was found to be technologically feasible but not financially feasible because it had a capital cost of between $5.5 billion and $32 billion in 2013 dollars. The full feasibility study can be accessed at This mass transit component is still a part of the Preferred Alternative for the I-70 Mountain Corridor. To learn more about the Preferred Alternative, please see the ROD.