I-70 & Harlan Street Bridge Replacement & Interchange Safety Improvements - Design Phase

About The Project

CDOT and prime contractor, ACC Built, have begun construction on a project to replace the I-70 bridge over Harlan Street. The bridge was built in 1967. With close proximity to Interstate 76, US 287 (Federal Boulevard) and CO 121 (Wadsworth Boulevard), this bridge experiences the highest daily traffic volumes in this corridor. Due to its age, heavy usage, and the seasonal weather, this bridge experiences frequent deck and concrete cracking. This deterioration has led to planned and emergency multi-day repairs causing delays and rerouting of traffic on Colorado’s busiest east-to-west corridor. All of these factors have contributed to the need for replacing the I-70 bridge over Harlan Street. 

As part of this project, additional safety improvements will be made to the Harlan Street, 48th Avenue, and westbound I-70 ramp intersection. These improvements were determined during a traffic study CDOT completed in 2021, which you can read about below. 

The graphic shows the final design for improvements to this interchange and describes the safety benefits of each potential improvement. Reconstructing the existing signals is a lower-cost solution that may reduce the likelihood of crashes. Providing pedestrian improvements will also improve the safety of people walking, biking, and driving vehicles through the intersections. 

I-70 & Harlan Intersection Improvements- English

I-70 & Harlan Intersection Improvements- Spanish

As the graphic shows, a new traffic signal is proposed on 48th Avenue at the new westbound I-70 ramp entrance. The new proposed traffic signal indications will be synced up with the existing signal at Harlan/48th. Here are some additional details:

  • At the Harlan intersection, the westbound approach from 48th Avenue will allow for one through lane and a dual left turn movement that is only allowed to proceed with a green arrow.
  • Additional signage and pavement markings will be installed to clarify which lane motorists need to be in to safely navigate through both the reconstructed traffic signal at Harlan/48th and the new signal at the proposed new westbound I-70 ramp access. 
  • The new signal at the proposed new westbound I-70 ramp access will not stop westbound traffic, and eastbound traffic will only be stopped when westbound traffic is turning left to access I-70. At all other times, the eastbound indications will be green and the westbound left indications will be a flashing yellow arrow indicating proceed when an acceptable gap is present.
  • To prevent traffic queues from backing up into the intersection at Harlan/48th, the westbound left green arrow onto I-70 at the new signal will be synced with the westbound 48th green phase as well as the northbound Harlan to westbound 48th left-turn green phase.

Download this video simulation to see how the traffic signal phasing is expected to work.

The following considerations were made in developing this intersection design:

  • Crash reduction potential
  • Maintaining traffic flow
  • Minimizing delay through intersections
  • Accommodating all modes of transportation
  • Impacts to businesses
  • Anticipated cost

Schedule and Travel Impacts

  • The westbound on-ramp at Harlan and I-70 will close for two days. Beginning Monday, April 10 at 7 a.m. through Wednesday, April 12 at 5 p.m., crews will be removing and replacing a sanitation pipe in the work zone. 
  • The detour currently in place for daytime ramp closures will remain in affect for the full closure. Please see the detour map.
  • Detour route for the westbound I-70 on-ramp is as follows: 48th Avenue turns into Marshall Street, turn left on 52nd Avenue, turn left on Wadsworth Boulevard, enter westbound I-70 from Wadsworth.
  • For information on the nearby Wadsworth project, please go to https://whatsupwheatridge.com/improve-wadsworth

Map showing detour route: West 48th to Marshall to 52nd to Wadsworth

Map showing detour route for Harlan Ramp Closure

Project Schedule

Construction: August 2022 to August 2024

I-70 Harlan Schedule.jpg

In 2021, CDOT completed a traffic study of the North Harlan Street and I-70 north and south interchange intersections. The study area was in the City of Wheat Ridge, which is immediately adjacent to the Town of Lakeside and the City and County of Denver, within Jefferson County.

This traffic study was a continuation from a 2015 safety study completed by CDOT, which identified the north intersection of the North Harlan Street and I-70 interchange as a safety concern location. This location experienced a higher than expected incidence of crashes during the study period of 2009 and 2014. The prevailing crash pattern and type was broadside crashes, which are statistically a more severe type of crash. Broadside crashes (or T-bone collisions) are where the side of one vehicle is impacted by the front or rear of another vehicle, forming a T shape with the cars. Engineering improvements to the intersection can help reduce the number of crashes, specifically broadside crashes. 

Early in the process of identifying potential safety improvements for the I-70/Harlan interchange, a roundabout was identified as a potential solution. A preliminary study from 2015-2016 identified safety concerns at the north intersection and recommended a single-lane roundabout as potential mitigation. However, that safety study only looked at the crash data and did not consider the potential impacts to traffic operations at the intersection.

A roundabout alternative was evaluated early in the 2020 study effort. Initially, the design team looked at the feasibility of reconstructing the two Harlan Street intersections north and south of I-70 as two single-lane roundabouts. It was determined that a single-lane roundabout would result in long delays and queues.

The exhibit below shows a conceptual layout of a roundabout at the north Harlan/I-70 interchange that allows for a three lane northbound approach. This layout was determined to be the minimum number of lanes required to avoid long delays and queuing. After developing this conceptual design, the roundabout alternative was eliminated from consideration for the following reasons:

  • The concept shows a significant impact to the existing undeveloped property in the northeast quadrant which would likely result in a total take of that property. It also shows impacts to accesses on the northwest corner.
  • Although the concept shows that a northbound three lane approach can fit under the bridge, when truck paths were checked it became apparent this geometry would result in overlapping of large vehicle paths. Further development of the concept would result in widening the approaches which will impact the existing bridge. This would also likely require moving the center of the circle to the north, resulting in significant property impacts in the northwest and northeast quadrants.
  • The westbound movements have the possibility of high speeds due to geometry and may result in high entry speeds and large speed differentials between the circulating and entering vehicles. Large speed differentials and high entry speeds in roundabouts often lead to high crash rates.
  • Additionally, the roundabout may result in high speeds of the westbound traffic at the pedestrian crossings. This could lead to pedestrian-vehicle incidents which are often injury or fatal crashes.

Harlan Roundabout Concept 1

Harlan Roundabout Concept 2