The Colton Crossing Flyover is a finalist in the 2015 ASCE’s Outstanding Civil Engineering Achievement (OCEA) award. Established in 1960, the OCEA Award recognizes a project that makes a significant contribution to both the civil engineering profession and society as a whole
One of the worst congested railway passages in the U.S. was eliminated on August 26, 2013, with the opening of the $93-million Colton Crossing Flyover, which separated 2 busy tracks in San Bernardino County, California.
Project designers at HDR devised an innovative approach to eliminate the chokepoint, located about 50 miles east of Los Angeles, by constructing a 8,150-foot flyover structure to take the Union Pacific Railroad’s east-west tracks 35 feet above the north-south tracks of the BNSF Railway. These are the 2 largest freight railroad networks in the U.S. Passenger rail lines also use these tracks.
Dubbed the “oldest bottleneck in U.S. history” by the U.S. Department of Transportation, Colton Crossing was originally built in 1883 as an “at grade” rail-to-rail intersection. Today, it hosts an average of 125 crossings daily.
To construct this project, engineers had to overcome physical, operational, and phasing constraints. A flyover structure to separate Union Pacific from BNSF tracks was identified as a means of improving freight and passenger movement in the region. However, a limited footprint would not allow typical sloped embankments for the approaches.
To solve this puzzle, HDR turned to a novel solution – cellular concrete. Though it had never been used in this quantity or at this height, cellular concrete offered the exact properties needed: its self-supporting nature meant there was no need for conventional retaining structures. All told, use of the material saved $45 million and expedited delivery by 8 months.
ASCE News Associate Editor Doug Scott interviewed Jeff Teig, national rail program leader for HDR and project manager for the Colton Crossing Flyover final design and construction support.
1. What is the most innovative or creative aspect of your project?
The unprecedented use of cellular concrete overcame a lot of the challenges and technical issues of the project – the tight constraints, the schedule, the continued operation of rail traffic. That was the biggie – being able to use cellular concrete to the scale we did.
2. What was the biggest challenge?
The biggest challenge was the schedule. The expiration date of the funding obtained for the project made it such that we had to do activities concurrently that are usually done sequentially. That made it very difficult because the NEPA [National Environmental Policy Act] documents weren’t completed by the time we started final design, and it’s usually not done that way. We were doing utility relocation design prior to having right-of-way approval, so there were a lot of things that had to be done concurrently in order to keep the schedule in place to make sure we kept the funding in place.
Just to give you an idea, we did a final design in 9 months that usually would take 2 years to do. We had over 100 people charge more than 40 hours from 10 different offices on this project in order to get it done. There were a lot of challenges, but the schedule was the biggest.
3. Did your project have any technical issues that you had to overcome? If so, what were they and how did you overcome them?
The technical issue was to maintain rail traffic through the heavily constrained corridor. We had residences to the south and I-10 to the north, then we had to have room for 4 tracks in place – 2 in service at all times. We also had to allow for future widening of I-10.
We had to design straddle bents across the 2 active mainlines for the connection track, which is the track used to change the direction of traffic from north to west or west to north. To top it all off, we had to lower the profile, so there was a huge depth issue we had to overcome for the straddle bents.
Another issue was the layer of poor soil at the surface that wasn’t strong enough to hold up conventional-type construction. That was another technical issue – how do we overcome the poor soils through the corridor?
The main way we overcame all those issues was with the cellular concrete. It helped us avoid removing the poor soils. It allowed smaller types of equipment to be used in construction of the corridor, which helped us keep rail traffic in service. And because we could leave the poor soils in place, we didn’t need shoring that would also have interfered with rail operations.
For the straddle bents, we did a combination of prestressed and posttensioning to get those to work on such a shallow scale. Plus, we had to design the bent caps as an inverted ‘T’ shape to get the grades to work.
The cellular concrete was also very quick to install.
4. What time and budget challenges did your project have and what did you do to overcome them?
It took 4 years from the start of considering doing a grade separation to getting the funding. We probably wouldn’t have obtained the funding without the TIGER [Transportation Investment Generating Economic Recovery] Grant and California bond funds. If those 2 things [hadn’t happened], we probably still wouldn’t have this project. Because of the funding, we had milestones we had to hit in order for those funds to remain in place. So we really had to accelerate the design.
5. Sustainability is one the 3 strategic initiatives here at ASCE. Describe how your project adheres to being sustainable.
The design life for the structure is 100 years. That’s typical for railroad bridges, but it’s not typical for other types of transportation structures. Because of the cellular concrete, we were able to keep the poor soil in place. So we used the existing soil rather than having to remove over 150,000 cubic yards of soil that would have had to be placed somewhere.
Sustainability was the whole reason for the project – to have better fluid mobility of the goods coming to and from the ports. The project reduced air pollution, reduced idling trains; reduced noise; reduced the use of fuel. There were a lot of things the project itself did that helped us get the funding, and they were based on sustainability issues. So the project itself demonstrated sustainability.