David from Golden writes, “What's driving you crazy? The merge (acceleration lane) from northbound Sheridan to eastbound US 6 is very abrupt. Traffic routinely backs up because of this. Can the merge either be lengthened by extending the merge area along the frontage road or add a meter on the ramp so that the flow of traffic is better regulated?”
No, not really and back to you.
You are correct David about that acceleration lane. It is woefully short to accommodate the speed needed to achieve to enter the freeway safely. 6th Avenue is one of Denver's early freeways. The portion of 6th Avenue west of Federal is largely still in its original configuration. As a result, several of the interchanges, including Sheridan, have outdated features and it’s that old design that is the reason for the daily slow traffic in from Lakewood. The ramp from Sheridan as it merges into the right lane on eastbound 6th Avenue is only about 100 feet long. In comparison, the ramp from Federal to westbound Highway 36 is about four times that long.
About 10 years ago, CDOT spent $11.5 million to replace the 6th Avenue bridge over Sheridan Boulevard but did nothing to change the access from Sheridan to eastbound 6th. While it looks like CDOT could just rework the right shoulder area to extend the ramp another 100 feet, there are certain guidelines they have to follow before any work can be done. The guidelines set for the length of highway ramps is found in the Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD). It would recommend a much longer ramp, however, CDOT says they don’t have the money or the room to build a longer ramp.
“The right of way is very constrained at this particular location and any attempt to have extended or expanded an auxiliary merge lane at that time would have resulted in right of way acquisition,” said CDOT’s Stacia Sellers. “That would include significantly greater costs due to the utilities, environmental clearance efforts and cost due to the very close proximity of the adjacent homes.”
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The other major design challenge for CDOT are not only the homes next to 6th Avenue but the location of the frontage road and sound walls that abut up to 6th Avenue. As it was explained to me by a former project engineer, in order to make room for the extended ramp, the frontage road would most likely be cut off at Wolff Street. A few homes might have to be purchased as part of eminent domain. That additional space could then be turned into a longer ramp separated by large sound wall barriers right up next to the highway and homes that remain on the south side of 6th Avenue. I have a feeling those current homeowners aren’t too concerned about how drivers merge onto 6th Avenue.
Specifically, to your question about adding meter lights to the ramp: One CDOT engineer tells me the short answer is they have no current plan to add ramp metering due to the configuration of the ramp. He explains saying the ramp is relatively short, meaning there isn’t enough space to hold traffic during ramp metering without it spilling back onto Sheridan Boulevard. They could speed up metering rates to allow for more cars to get through but that would make any flow improvement on 6th Avenue greatly diminished.
The other problem is because the ramp is so short, there is less distance to accelerate to freeway speed after being stopped at the meter light. I’m told by the CDOT engineer that effective ramp metering necessitates operating the ramp meter when freeway flows are heavy but not yet at stop-and-go conditions. Due to the short length of the ramp and the merge from Sheridan to 6th Avenue, there is concern that adequate acceleration space could not be provided downstream of the ramp meter's stop bar.
Ultimately, the combination of needing to rapidly release vehicles due to the short storage space and the slower entering speed due to the short acceleration space would likely negate any potential ramp metering benefits.
As you can tell, CDOT knows this is a problem area and would like to fix the interchange by bringing it up to current design standards, but any thorough assessment would be needed first to determine a rough cost of improvements to the ramp, freeway mainline, and adjacent frontage road as well as impacts to retaining walls and noise walls. That would likely make the cost several times higher than typical cost for ramp metering installation, which is around $400,000 per location.
My experience is that the left lane moves a touch faster past Sheridan than the center or the right lane but then you are faced with the difficult challenge of merging over two lanes by the time you get to Federal if you want to get to I-25.
Denver7 traffic anchor Jayson Luber says he has been covering Denver-metro traffic since Ben-Hur was driving a chariot. (We believe the actual number is over 25 years.) He's obsessed with letting viewers know what's happening on their drive and the best way to avoid the problems that spring up. Follow him on Facebook, Twitter or Instagram or listen to his Driving You Crazy podcast on iTunes, Stitcher, iHeartRadio, Spotify or Podbean.
