This map shows the 18 predictable freeway bottlenecks identified by the Denver Regional Council of Governments. Zoom in or click on any of the blue balloons to read about each one’s congestion statistics, the key causes and possible remedies for the problems.

View Metro Denver’s Freeway Bottlenecks in a larger map

Denver’s most notorious freeway bottlenecks are in the crosshairs of transportation planners.

But without reliable and consistent funding as ammunition to build the improvements that would untangle these congestion points, they’ll be shooting blanks.

You know them by name, likely. They tie up traffic regularly and frustratingly. Interstate 70 at Floyd Hill. Sixth Avenue at Bryant Street. Interstate 70 through the Stapleton area. Boulder Turnpike from Foothills to Davidson Mesa. Interstate 25 at Broadway and Santa Fe.

Use your cursor to move this Google Street View around the I-70/Floyd Hill area, the freeway segment with the longest congestion delay of seven minutes and 43 seconds for weekend peak hour traffic.

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And the mother of traffic bottlenecks, I-25 in the Central Valley between Speer and 20th Street – the most heavily traveled segment of roadway in the Rocky Mountain West.

“A lot of these you’ll hear about every morning or afternoon on the radio traffic report,” said Steve Cook, transportation planning program manager for the Denver Regional Council of Governments.

DRCOG has put together updated profiles of 18 infamous bottlenecks on the metro area’s freeway system and posted it online last week. It reads like a rap sheet on some of the worst miscreant commuting corridors. What’s key to labeling a bottleneck is, foremost, predictability. Each afternoon, when work gets out, drivers know they will hit a backup northbound on I-25 in Adams County approaching 84th Avenue.

Cook makes no attempt to rank them – how could he anyway? By time lost, total traffic delayed, drop from free-flow speeds, crashes? These may not even be the 18 bottlenecks on which all other metro drivers would agree, and the list doesn’t include jams on surface arterial streets like Wadsworth or Colorado boulevards.

“It’s not meant to be the full list,” Cook said.

But they are the iconic bottlenecks of Denver, and the roster gives all the vitals. It provides descriptions of the particular problems that are unique at each location, the baseline current traffic conditions, three-year crash data from 2002-2004, the Colorado Department of Transportation’s safety service level rating that estimates the potential for accident reduction, rush-hour delays and speeds and, finally, possible projects that would improve the situation.

The outdated cloverleaf interchange at I-270 and Vasquez Boulevard had the highest delay per person in the metro area, four minutes and 34 seconds; only I-70 from Floyd Hill to Idaho Springs had more delay.

Some projects are funded or in line for funding, such as the I-25 bottleneck at Santa Fe. Some are in the study phase to get environmental clearance so that federal funding can be used, if ever available. Some projects are visible on the radar scope and some are merely on a wish list.

Cook says DRCOG looked for bottlenecks of all different types, and wasn’t disappointed. They have many different characteristics. The I-70 mountain corridor, for instance, is predictably bottlenecked during ski season weekends, particularly eastbound on Sunday afternoons.

“And U.S. 36 leaving Boulder at Davidson Mesa, if you compare that to 225 at I-25, they’re not in the same league, but it is something that has a unique cause, maybe after a football game,” Cook said.

These 18 bottlenecks cause a total of 16.8 million person-hours of delay per year that cost the local economy $444.3 million annually, DRCOG calculates. An average of 1,130 crashes per year occurred at these locations between 2002 and 2004.

This Google Street View shows I-25 between 20th Street and Speer Boulevard, along the busiest segment of freeway in the Rocky Mountain West.

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So what causes bottlenecks?

DRCOG noted that “every freeway includes decision points that may affect the consistent speed of vehicles, such as on and off ramps, merge areas, weave areas and lane drop locations.” Bottlenecks also form in areas where freeways had awkward curves, hills, narrow shoulders on either side and tunnels – remember how traffic almost inexplicably slowed on I-70 under the old Stapleton runway tunnel?

A lane-drop is when a freeway loses a through lane, such as when five-lane I-25 northbound becomes four lanes at the Interstate 225 junction, then down to three lanes when the right lane jumps off at Santa Fe. When the number of vehicles increases, the merging forced by a lane drop slows traffic like squeezing an accordion.

A weave lane is where entering traffic mixes with exiting traffic, most apparent at cloverleaf ramps such as Sixth Avenue Freeway at Wadsworth or the problematic Sixth-Bryant-I-25 weave.

Fixes can be expensive.

CDOT resolved one of the metro area’s most dangerous weaves when the T-REX project rebuilt the Full House interchange at I-25 and I-225. Southbound I-225 traffic entering I-25 from the left side but wanting to exit at Belleview Avenue had to weave across three busy through lanes to get there in a very short distance. Now, I-225 traffic feeds onto I-25 from the right, via a tunnel that separates the flow, and drivers headed to Belleview simply slips to the right at the exit ramp, never touching I-25.

Northbound, traffic entering I-25 at Belleview faced a hazardous weave with vehicles exiting at I-225. There, CDOT used a “braided ramp,” a bridge that carries traffic entering from Belleview up and over the rampt to I-225 – with a slip ramp allowing Belleview drivers to get to I-225 as well.

But structures such as tunnels, bridges and retaining walls, are the most expensive elements of a transportation project.

“Hopefully this list will stimulate conversation and get people to think about how to address them,” Cook said.

Here are the aggravating 18:

C-470 (both directions) from US-285 to Quincy Ave.
C-470 (eastbound) east of Santa Fe Dr.
C-470 (both directions) from Yosemite St. to I-25
I-25 (southbound) south of County Line Rd.
I-25 (both directions) from Broadway to Alameda Ave.
I-25 (both directions) from Speer Blvd. to 20th St.
I-25 (both directions) north of US-36/I-270 Interchange
I-70 (both directions) from Twin Tunnels to Floyd Hill
I-70 (eastbound) from I-25 to York St.
I-70 (eastbound) east of I-270 EB Interchange
I-225 (southbound) from Yosemite St. to I-25
I-225 (southbound) from Alameda to 6th Ave.
I-225 (northbound) from Parker Rd. to Yale Ave.
I-270 (both directions) at Vasquez Blvd.
US-36 (eastbound) from Foothills Pkwy. to Davidson Mesa
US-36 (both directions) from Interlocken Loop to Wadsworth Blvd.
US-6 (both directions) at Wadsworth Blvd.
US-6 (both directions) from Federal Blvd. to I-25