Community Cycles Preferred Option(s) for the Iris Improvement Project

Alexey DaviesAdvocacy, News

It is time for everyone to weigh in on the proposed safety improvements to Iris Avenue. 

Arterials make up just 17% of Boulder’s street system, however they account for two-thirds of the city’s fatal and severe traffic crashes. In 2022 City Council unanimously agreed to move forward with the Core Arterial Network (CAN) to improve safety for all modes and provide equitable mobility on a key set of interconnected arterials.

The city has put forward four design alternatives to make Iris safer for all users. Alternatives A and B require no expansion of the current right of way. Alternatives C and D are major road reconstruction projects that require extensive right of way acquisition, mature tree removal, and relocation of utilities like water, sewer, lights, and power. 

Community Cycles supports Alternative A or B based on safety and feasibility.  


We can expect the four-lane widening configurations (alternatives C and D) of Iris to be at least four times more expensive than the three-lane configurations (alternatives A and B). Our cost estimate for alternate A and B is based on the cost of Baseline Phase 1 & 2 (approximately $5M). The cost of alternatives C/D are more difficult to estimate. The reconstruction of 30th street (from Arapahoe to Colorado) will cost at least $5.8M for .5 miles. The recent North Broadway reconstruction cost was $11M, not including the Fourmile Creek underpass flood mitigation work.  We estimate that the cost for widening and reconstructing the 1.2 miles of Iris under alternatives C or D will be at least $20M in today’s dollars. Based on CDOT’s average inflation rate in recent years (~10%), the project cost will likely exceed $135 million by the time of implementation. 


The 30th street corridor study was completed in 2015 with the preferred alternative to maintain 4 travel lanes and add protected bike lanes. Since then we have gotten one protected intersection thanks in large part to CU and public matching funds.  The Arapahoe to Colorado segment of 30th is funded and work just began.  The segment from Colorado to Baseline is still unfunded.  Based on this example we estimate a completion date 20 years in the future for Alternate C & D.


Alternates C & D do not reduce the most common crash type, rear-end automobile crashes when vehicles are turning left.  Most cyclist crashes are at intersections, and the four-lane options C & D may not provide fully protected intersections due to space constraints.  In addition, the crossing distance is greater for pedestrians for the four-lane options, which increases risk. Alternatives C & D will not slow vehicle traffic by design, and current median vehicle speeds would likely remain well above the current 35 mph speed limit.


Alternates C & D do not help shift travel behaviors away from carbon-intensive driving as much as A & B do. The most recent IPCC report highlights the need for a 48% reduction in carbon dioxide emissions by 2030. The long build times for C & D are inconsistent with this urgency. Additionally, higher vehicle speeds associated with the four-lane options will increase acceleration, braking, energy use, and particle emissions from tires, brakes, and road dust relative to A & B. They also result in much higher noise, affecting environmental quality for adjacent residents and those walking or biking along Iris.

While Community Cycles supports Alternatives A & B, we do have some negotiable criteria for acceptance of Alternate B, and some non-negotiable criteria such as signal & turning restrictions.  Alternate B, with the two-way cyclepath, has cyclists traveling in the opposite direction of vehicle travel. We fear that drivers trying to enter Iris will not be looking to the right for cyclists traveling from that direction. Our criteria describe ways to mitigate these and other risks. We note that alternate B has some benefits, notably by providing better emergency response options, and easing snow removal due to the fewer lane-miles, wider path and the greater sun exposure on the north side of Iris.


Please write Council with your support of Alternate A or B and / or sign up to speak at City Council meetings. We have talking points or a short templates to assist in your message

Thank you!
You can read more about our analysis on the Iris for All webpage.  For information about Community Cycles vision and educational materials, please visit Boulder for All – A new vision for transportation in our Community.  The City of Boulder storymap is here.