Frequently Asked Questions

Select any of the topic buttons below to expand or collapse a full list of answers to frequently asked questions about this study.

What is a PEL Study?

A Planning and Environmental Linkages study is a process typically used to identify transportation issues and environmental concerns in a large corridor or a specific location. It is generally conducted before any project construction funding is identified, and before specific problems and solutions are known. At a high-level, a PEL study:

  • Reviews existing environmental resources and examines the existing infrastructure and congestion conditions Identifies corridor needs (i.e. safety, congestion)
  • Defines and evaluates potential improvements Identifies possible impacts from proposed alternatives
  • Develops a vision and implementation plan for priorities large and small

Read more information about CDOT’s Planning and Environmental Linkages Program.

What is NEPA and how does it relate to the PEL?

The National Environmental Policy Act (NEPA) requires projects that have a federal nexus (Federal funds are involved, Federal permits, new or revised access to the interstate system, or other Federal approvals are required) to analyze the project’s effects on the environment prior to a Federal Agency making approvals or taking an action on the project.

Since CDOT uses federal funding to maintain and improve the interstate system throughout Colorado, most improvement projects on the Interstate must first undergo some level of NEPA review (Environmental Impact Statement (EIS), Environmental Assessment (EA), or a Categorical Exclusion (CATEX)).

A PEL uses transportation planning decisions and analysis, including purpose and need, identification of preliminary alternatives, and elimination of unreasonable alternatives, to inform NEPA. This helps reduce and eliminate duplication of work in the planning and NEPA processes.

What is the purpose of I-25 Central PEL?

The I-25 Central PEL study is examining Interstate 25 (I-25) between Santa Fe Drive/US 85 and 20th Street in Denver. The purpose of the recommended transportation improvements is to reduce congestion and improve safety and travel-time reliability for the movement of people and goods. The improvements will also consider access to and from I-25 as well as connectivity across I-25 for bicycles, pedestrians, transit and local traffic. See the Draft Purpose and Need statement.

What are the goals of the study?

In addition to the core purpose of the study, numerous goals also have been identified. These include:

  • Investigate opportunities to improve mainline geometry and design to meet current standards and address substandard: Stopping-sight distance, clear zones, narrow lane widths, and narrow shoulder widths
  • Investigate opportunities to use and/or not preclude emerging technologies to improve the safety, capacity, and management of mainline operations
  • Provide efficient access to major parallel routes and corridor destinations
  • Consider the impacts and benefits of proposed improvements on the local network
  • Improve connectivity across I-25 and the South Platte River for all modes
  • Consider the impacts of adjacent high-density redevelopment and the related potential changes in travel demand on I-25
  • Consider the impact of congestion improvements on southbound I-25 in relation to improved operation for southbound RTD buses
  • Consider the impacts and benefits on freight movement in the corridor
  • Consider the ability of improvements to the mainline and local network to improve person-trip connectivity
  • Consider the effects of improvements on the South Platte River and the surrounding communities
  • Consider the effects of expanded right of way on adjacent land uses
  • Consider the ability of improvements to provide community and environmental enhancements
  • Consider the ability of improvements to support economic development opportunities in the metro Denver area

What is the I-25 Central PEL Schedule?


Are you working with any other agencies and considering their goals?

This study is highly collaborative. In addition to community organizations and local businesses, CDOT is working with the City and County of Denver; the Federal Highway Administration; RTD; and the Denver Regional Council of Governments. All of these groups provided input on this PEL’s purpose, needs, goals, and objectives, which reflect the many different goals of the respective groups and agencies. Using the purpose, needs, goals, and objectives as the basis for the alternative’s evaluation process ensures that the outcomes of this study support and balance the overall missions and priorities of all study stakeholders.

What are the opportunities for public and agency participation?

Understanding the ideas, perspectives and needs of stakeholders in the corridor area is critical to building broadly supported decisions and solutions. The I-25 Central PEL study has multiple ways to get involved and stay informed.

Stakeholder Focus Group

The stakeholder focus group (SFG), is a group of representatives from a wide range of local stakeholders throughout the corridor. This group includes people from neighborhood associations, businesses and business coalitions, and non-profit organizations. The SFG meets at key milestones to review the work to-date and provide feedback to the project team. Key milestones for this study include:

  • Development of the project’s purpose and need
  • Completion of the level 1 evaluation
  • Completion of the level 2 evaluation
  • Completion of the level 3 evaluation
  • See the full list of the organizations that are a part of the I-25 Central SFG.

Public Open House

As part of the alternatives evaluation process, the I-25 Central project team hosted a public open house. This provided all interested persons the opportunity to learn more about the alternatives being evaluated, the initial results of the evaluation process, and ask questions directly to the project team.

Download the materials from the Open House.

Project Website

In addition to in-person engagement opportunities, current information about the study’s progress to-date as well as feedback opportunities are always available within this site.

How are I-25 Central PEL alternatives being developed and evaluated?

An initial list of alternatives was developed through a series of brainstorming discussions and interviews with key project stakeholders, project team members, and representatives from the public including members of neighborhood organizations, local business owners and coalitions, non-profit organizations, and others.

The alternatives are being evaluated through a three-level process. Initial evaluation examined whether an alternative meets the project’s purpose and need. The second level of evaluation examined how well an alternative meets the project goals. The last level of evaluation will examine the detailed tradeoffs between alternatives and make final recommendations about which alternatives should be carried forward into the NEPA process.


Alternatives are eliminated from further consideration at any level of evaluation if they are determined to not meet the projects purpose and need, or if a fatal flaw in their design is identified. It should be noted, however, that just because an alternative is eliminated from consideration it does not mean that elements from that alternative could not be carried forward. Upon removal from consideration, alternatives will be examined and positive elements or concepts from the alternative could be combined into existing alternatives, or recompiled into new alternatives to be carried forward.

How will the final alternative(s) be selected?

A multi-stepped alternatives evaluation processes is being used to refine different alternatives and ultimately make a recommendation on which ones should be moved forward into future studies, such as NEPA studies. This evaluation process is centered around understanding if an alternative meets the project’s purpose and need, how well it achieves the identified goals and objectives, and how large the potential impacts could be.

Subsequent to the PEL, a NEPA study will further develop alternatives and select a final, single, alternative for implementation. To learn more about NEPA, refer to Section 1 on this page.

What solutions are possible before considering adding lanes?

The study is considering a wide range of alternatives to improve the corridor, a number of which do not include adding lanes to the highway. These types of solutions include:

  • Assisting and supporting RTD and Denver in improving the transit system;
  • Assisting and supporting RTD and Denver in improving access to transit;
  • Improving bicycle and pedestrian routes;
  • Implementing congestion pricing;
  • Optimizing traffic flow using existing pavement through the use of intelligent transportation systems (ITS) and travel demand management strategies (TDM);
  • Better managing access to and from the interstate to smooth and improve traffic flow; and
  • Improving the geometrics of the roadway.

Why are more lanes being considered?

Population in the Denver region is expected to increase by 1.2 million people between 2015 and 2040. This growth will result in an increase in congestion on I-25 Central. Additional lanes on the highway are being considered and evaluated to understand how they might be able to help meet the I-25 Central PEL’s stated purpose, part of which is to reduce congestion for the movement of people and goods.

It should be noted that the I-25 Central PEL is considering a wide range of alternatives and concepts to improve the corridor – some with more lanes being considered and some with no additional lanes being considered. To understand the needs of the corridor, the study is using the 2040 DRCOG regional travel demand model to estimate what the future travel demand and resulting congestion will be on I-25 Central. This model includes projected employment and population data and accounts for already planned transportation improvements—including bicycle, pedestrian, transit system, and other roadway improvements. This type of data driven analysis is being utilized to help determine the appropriate number of lanes.

Why are you considering managed lanes (HOV or toll lanes)?

In December of 2012 the Transportation Commission adopted Policy Directive 1603.0 requiring that managed lanes be strongly considered during the planning and development of capacity improvements on state highway facilities. Managed lanes provide the ability for CDOT to respond to changing traffic conditions and provide operational flexibility and efficient operation of the multi-modal transportation system infrastructure by maximizing the number of vehicles or the number of people traveling in a given corridor. As congestion increases in a corridor, like I-25, managed lanes can provide greater reliability of travel and also promote alternative travel choices. The challenge for transportation planners and highway engineers is to maximize the operation of transportation infrastructure by considering flexible, cost effective strategies for sustaining or enhancing the movement of people and goods.

Managed lanes will be considered as a potential element for the highway alternatives. The specific type, design, entry/exit, and use qualifications of the managed lanes have not yet been determined.

Will the footprint of I-25 be widened? If so, why?

Due to the existing deficiencies of the highway, the footprint may need to be widened. This study is examining a range of alternatives some of which require only minor widening while other alternatives have a wider footprint. This widening may be needed, at a minimum, to bring the existing highway up to current design standards (such as adding shoulders for emergency response and vehicle breakdowns and reducing the sharpness of curves to improve safety). Additional widening may be needed to provide congestion relief and better travel time reliability.  Details of where and how much I-25 may be widened will be determined in future studies.

How is access to and from the Interstate being considered?

The evaluation process in the PEL is examining access to and from the interstate in an effort to maximize the efficiency of the system while also promoting safety. This can be achieved by improving the geometry of access points—such as adding/improving acceleration and deceleration lanes so vehicles can reach an appropriate speed before entering or leaving highway traffic—and by appropriately spacing access points to/from the interstate. Both of these access elements are being evaluated through this PEL study.

For geometric improvements to access, the study team is looking at existing access ramp design and assessing what improvements are needed to bring the ramps up to current engineering design standards. This includes improvements to visibility, curvature, acceleration/deceleration lengths, etc.

For ramps spacing improvements, the study is examining a wide range of options to balance the needs and desires for convenient access to/from the interstate with the study’s purpose which is partially to improve safety and reduce congestion. Improvements being considered which would improve ramp spacing include:

  • Combining multiple access points together using collector/distributor roads (Collector/distributor roads are dedicated lanes on the side of the highway used by vehicles entering and exiting the highway, these lanes usually have a lower speed limit and facilitate vehicles entering and exiting the highway without impacting the through lanes.);
  • Moving access points to connect to the interstate at different locations;
  • Closing access points; and
  • Adding new access points.

The potential congestion, travel time reliability, safety, and other transportation related benefits and impacts of modifying access to the interstate will be examined and documented in this PEL study; however, a final conclusion on access closures or openings will not be made. Additional analysis to fully understand the potential benefits and impacts access changes may have—including to other areas of importance such as businesses and development impacts— will be completed in future, more focused studies.

Is the process taking into consideration the values of Denver residents?

The heart of this study is understanding what is important to the residents and users of I-25 Central. To understand this, the I-25 Central study is conducting a public involvement process that is more robust than many other PEL studies. Many different stakeholders have been integral to the study and interviewed, including Denver city councilmembers, Denver public offices, nonprofits, businesses, and community organizations to understand the interests and values of Denver residents. In addition to being interviewed, many of these groups are part of the study’s Stakeholder Focus Group. The I-25 Central team is in regular communication with this group—which includes local neighborhood organizations, nonprofits, environmental advocates, bicycle and pedestrian advocates, businesses, and schools. The input from these stakeholders is being used to shape and refine alternatives and is also being used in decision-making of the study. Beyond the interviews and the Stakeholder Focus Group, a public survey was conducted and nearly 1,500 people responded. Input collected from this survey has been considered during the alternatives development and screening process, and will be considered as projects move into NEPA.

Public/community engagement will continue to be an important aspect throughout the I-25 Central PEL study and all future projects. This engagement will continue to ensure that the priorities and values of residents and users of I-25 Central help shape the decision-making process and outcomes along the corridor throughout the planning, design, and construction processes.

Will the highway's impacts to the environment be considered and reduced and/or minimized?

A PEL study looks at existing conditions of environmental resources within a corridor which provides the baseline information to consider as alternatives are developed and evaluated in the PEL. Within this type of study, potential environmental impacts are evaluated at a high level as they relate to the amount of design available. As projects move from a PEL study into NEPA, environmental impacts are assessed and reduced, minimized, or mitigated as needed.

How many vehicles travel all the way through the corridor as opposed to within it?

Analysis of available traffic data indicates that 20-25 percent of vehicles travel through the corridor end to end between US 85/Santa Fe Drive and 20th Street.

What is induced demand and will any effects be taken into account?

Induced demand happens when road improvements entice additional travelers to use the road (such as diversion from other routes, new or longer trips, and trips from new development).

Travel demand on I-25 and the local street network is being analyzed with travel simulation models for the project alternatives.  A primary goal of the study is to understand how people are using the existing transportation network to complete trips within the study area. The alternatives analysis will consider traffic volumes on I-25 and parallel facilities.

This study will take into account the efforts made with RTD and the City and County of Denver to analyze strategies that encourage other modes of travel, such as improvements to transit, bike and pedestrian facilities, and technology solutions like Transportation Demand Management (to learn more about TDM, refer to Section 8 on this page). 

How is the study addressing congestion on the highway and surrounding roadway network?

This study is addressing congestion on the highway and the surrounding roadway network by first understanding the root causes of congestion—such as the overall travel demand, the impacts of special events, the impacts of crashes, etc.—and then identifying potential solutions that could help address these root causes of congestion. Some congestion solutions being considered include travel demand management (TDM) strategies to reduce the overall demand to use I-25, transit improvements to encourage people to use other modes of travel other than driving on I-25, and highway capacity improvements to better accommodate the travel demand.

To understand how these kinds of improvements may help reduce congestion, the I-25 Central PEL study team is examining congestion a larger network level. To do this, the traffic analysis area for this study was expanded to include a much larger area than just the I-25 Central corridor. The traffic analysis area includes the roadway network generally bounded by US 36/I-270 to the north, Washington Street/Brighton Boulevard/Speer Boulevard to the east, University Boulevard/Mississippi Avenue to the south, and Federal Boulevard to the east . In addition to this, the traffic analysis has also included an analysis of the bicycle, pedestrian, and transit networks. Expanding the traffic analysis area to include such a large region beyond the immediate study area will allow the I-25 Central PEL study to better understand the how the larger transportation network works together to serve the travel demand. 

Is safety a priority for the study?

Yes, safety is one of the primary needs identified and listed in the study’s Purpose and Need statement that has helped craft concepts and evaluate alternatives. This study is modeling safety performance and working hard to ensure that safety is improved on I-25 Central.

Are you seeking to align I-25 Central solutions with other concepts, like Front Range Rail?

This study is considering concepts and alternatives in context with existing and on-going planning efforts including local plans—such as Denver’s bicycle, pedestrian, transit and development plans—and more regional plans—such as Front Range Rail.

What new east-west crossings will be added for bicyclists and pedestrians?

Accommodating bike and pedestrians across I-25 is an important part of the study, which means bike and pedestrian crossing’s will be fully considered in all alternatives. Working with City and County of Denver staff, sidewalk and trail improvements identified in Denver’s planning documents will be part of this study document, and opportunities for additional crossing locations will be evaluated.

Will alternatives include multi-modal options, other than for automobiles?

The study team has worked with RTD and Denver to understand and support expansion and access to multi-modal options. Locations for innovative “mobility hubs,” where travelers can more easily shift from vehicles to transit or trails, will also be suggested. Opportunities for  improved bicycle and pedestrian crossings, including enhanced experiences such as a “lid” option, will also be highlighted in the study report but will have to be further analyzed in subsequent and more detailed studies.  

is safety a priority for the study?

Yes, safety is one of the primary needs identified and listed in the study’s Purpose and Need statement that has helped craft concepts and evaluate alternatives. This study is modeling safety performance and working hard to ensure that safety is improved on I-25 Central.

Are there real projects, or is this just another study?

There’s a real need for improvement on the I-25 Central Corridor. The cityscape is changing, the population is growing, and more and more people and goods are moving around and along the corridor. For these reasons, we believe this study is an integral component to real results. There are several projects on I-25, from Santa Fe to 20th, which have been studied in the past and could proceed more quickly if and when funds are made available.

To the south, more than ten years ago the Valley Highway EIS studied and generated six projects, or “phases,” from Santa Fe to 6th Ave. The recently completed construction projects at Santa Fe and 6th Ave account for only half of the planned work. Remaining phases in this area, yet to be funded, include improvements to Alameda, an improved connection from Alameda to north I-25, railroad track realignment, and I-25 improvements from Alameda to 6th Ave

On the north side of the corridor, studies of the 23rd Ave and Speer bridges have already highlighted poor remaining structural life, deficient clearance for trucks, outdated access ramps, and poor bicycle/pedestrian connectivity.

Each of these projects-in-development are included in this PEL study, for a holistic visioning of the future of I-25. In addition to these projects-in-development, the goal is that the I-25 Central PEL will result in alternatives that will improve the full corridor.

How can I see the results?

Materials and concepts have been made available to the public throughout the study and the final PEL study will be available in the Fall of 2019. You can get involved in the process before anything is decided. Study materials, including preliminary results and materials presented at public and stakeholder meetings, are available for download. Interested persons can also register to receive the periodic study update email blast which provide information on the current progress of the PEL study.

Will alternatives include multi-modal options, other than for automobiles?

The study team has worked with RTD and Denver to understand and support expansion and access to multi-modal options. Locations for innovative “mobility hubs,” where travelers can more easily shift from vehicles to transit or trails, will also be suggested. Opportunities for  improved bicycle and pedestrian crossings, including enhanced experiences such as a “lid” option, will also be highlighted in the study report but will have to be further analyzed in subsequent and more detailed studies.  

Is safety a priority for the study?

Yes, safety is one of the primary needs identified and listed in the study’s Purpose and Need statement that has helped craft concepts and evaluate alternatives. This study is modeling safety performance and working hard to ensure that safety is improved on I-25 Central.

Will the effect of new emerging technologies, such as autonomous and connected vehicles, be considered?

Autonomous and connected vehicle technology is at the forefront of research at this time, but the impact on future traffic volumes is currently unknown. Whether this technology will result in increases or decreases in trips and vehicle miles traveled (VMT) is being debated by industry experts. A large unknown is how long it will take to create market penetration of the given technology to create a significant impact on traffic volumes or miles driven. Traditionally, market penetration depends on economic feasibility and affordability.

CDOT is looking at using new technologies that will benefit traffic operations and safety for the entire state with the focus on higher traffic volume highway corridors such as I-25. This study is modeling an estimated range of possible effects of connected and autonomous vehicles will be documented in the PEL report to inform the development of alternatives.

Is the study considering Transportation Demand Management (TDM) solutions?

TDM is one of many alternatives being considered as part of the study. TDM solutions help people consider and use new alternatives to meet their travel needs, for example by altering their mode of travel, their time of travel, routes, etc. Managed lanes are one option of a TDM solution being considered in this study, which can influence people’s travel behavior. Another such solution under consideration is congestion pricing. This strategy, in order to relieve traffic congestion, imposes a fee for traveling on a roadway or within a specified area. These solutions/strategies are being examined to be implemented on their own as well as to be paired with other solutions to form a full range of improvements.