Computer simulation shows the planned southbound to eastbound flyover ramp from Santa Fe Drive to C-470 that CDOT expects to put out for contractor bids next month.

A project aiming to bring a big improvement to southwest metro commuters is going out to bid next month.

The Colorado Department of Transportation expects to advertise for bids Jan. 28 for the Phase 1 reconstruction of the C-470 interchange at U.S. 85, Santa Fe Drive. This $25.8 million phase of an overall $60 million interchange overhaul will build a huge and dramatically high flyover ramp to take southbound Santa Fe traffic directly onto eastbound C-470.

The south-to-east ramp will take the left turns out of the traffic jams that fill the Santa Fe overpass at C-470 waiting for the turn arrow.

But that’s not the only traffic improvement this project will bring.

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The entrance to the flyover ramp will be north of the nearby County Line Road intersection, so this means taking more than a thousand cars out of having to go through that intersection in the peak hour of the rush hours. That traffic instead will pass over County Line road on a bridge to the west.

Also, the flyover ramp will merge with the existing eastbound on-ramp first before reaching C-470, and then be lengthened about 1,100 feet farther to the east that where the current on-ramp merges into C-470.

This will eliminate the uphill climb there as the freeway comes up from the Platte River bottoms onto the highlands from which Highlands Ranch got its name.

That means entering traffic will have a better opportunity to get up to speed with the 65-mph flows on the highway when merging.

Diagram shows the new flyover ramp to be built and how it fits into the new entrance ramp, auxiliary lane, in yellow, and RTD light rail extension, in blue. Click on the image to enlarge it.

And finally, that right lane will be extended all the way to a “must exit” lane at Lucent Boulevard – what highway planners call an “auxiliary lane.” This will give C-470 drivers much more distance within which to complete their merging and weaving with traffic getting off at Lucent. And it means Santa Fe traffic headed to Lucent won’t even have to do any merging at all, just stay in the auxiliary lane to the Lucent exit.

The project has a mish-mash of funding sources. Douglas County is putting up $5.5 million; there is $9.3 million in federal funds allocated to it through the Denver Regional Council of Governments, including $3.8 million in federal stimulus funds through the American Recovery and Reinvestment Act; another $9.3 million in federal earmarked funds; and $2.1 million in CDOT funds.

One more element makes the project challenging to highway designers and interesting for motorists. Two freight railroad mainlines cut through the area along Santa Fe, and the RTD light rail line that now ends at Mineral Avenue is supposed to be extended through here as well on its own high flyover bridge.

The FasTracks Southwest Corridor extension to Lucent Boulevard will have a high bridge that crosses over the freight lines as well as the new highway ramp.

Combined with the topography here at the steep hill overlooking the Platte, it will make for a structural multi-stack and multimodal set of bridges for highway, freight and transit.