Interstate 70 at Highway 40 has made its way onto the short list of major highway bottlenecks in the United States.

The downtown St. Louis interchange boasts a peak average speed of 39 mph and a nonpeak average of 47 mph, according to the report. It found that the worst time to drive was 5 to 6 p.m. each day.

Of course, this location is a spaghetti bowl of interstate highways that converge just west of the Poplar Street Bridge. It's quirky, too. Say you're driving south on I-70 through the depressed section and need to get to westbound Highway 40 (Interstate 64).

Good luck with that. There is no direct connection.

The American Transportation Research Institute and the Federal Highway Administration ranked the interchange as the 28th-worst bottleneck. The rankings track "congestion trends and conditions for infrastructure that is vital to freight transportation."

The results were released last month.

The research institute said it used truck position and speed data pulled from "wireless onboard communications systems" commonly used by the trucking industry.

In all, the group ranked 250 highway interchanges and highway segments. Not all really qualify as bottlenecks, said Daniel Murray, vice president of research at the institute.

Two other St. Louis interchanges made the list: Interstate 70 at Interstate 270 (ranked No. 164 on the congestion index) and Interstate 55 at Interstate 255 (ranked No. 174). Those highway segments aren't as likely to be classified as chokepoints.

To earn its way onto the list, Murray said, there has to be a significant amount of truck traffic and, in the majority of cases, a substantial reduction of speed from what it is when traffic is flowing freely.

The congestion study would appear to lend support to those who pushed for the new Mississippi River bridge north of the Edward Jones Dome. Alleviating congestion on I-70 and the river bridges has long been held out as a reason to build another crossing.

BURNING UP OVER TRAFFIC?

Ever wonder how much extra gasoline your car burns while it idles in traffic jams?

For St. Louis car commuters, the Texas Transportation Institute put that number at 14 gallons (roughly equal to a week's worth of gasoline for the typical commuter) last year. The national average for large urban areas was 11 gallons last year. What's more, traffic congestion costs the typical St. Louis commuter $642 a year, equal to the national average for similar-size regions.

The 2011 Urban Mobility Report, as we reported in the Along for the Ride blog last week, found that while overall congestion has let up across the country — primarily because of the stagnant economy — it is a heck of a lot worse than it was in the early 1980s.

"The economic slowdown points to one of the basic rules of traffic congestion — if fewer people are traveling, there will be less congestion," the authors concluded.

The annual TTI mobility report found congestion will increase slowly over the next decade and said transportation planners should combat it through smarter management and targeted projects to increase road capacity in heavily traveled corridors.

Here's how St. Louis stacked up:

— Yearly congestion delay per driver: 30 hours (Rank: 34th among all U.S. cities/regions).

— Traffic "operational treatments" — including highway incident management and signal coordination on arterials — saved the region a collective 1.98 million hours in traffic delays. (Rank: 27th)

— The commuter stress index — measured by the ratio of travel time in the peak times to free-flow conditions for peak directions of travel — ranked 62nd nationally among 101 areas.

Q. On westbound Highway 40 at the Vandeventer on ramp, the entrance lane from Vandeventer has a solid (no crossing) line, but only for a limited distance. Because westbound 40 traffic is traveling at a higher rate of speed than the entering Vandeventer traffic, I believe it creates a dangerous situation (i.e., entering slower-moving vehicles merging right, immediately). To make it safer, would it not be prudent to extend the solid white line to remind entering Vandeventer traffic not to merge until it is safe? — R.H.

A. The Vandeventer ramp actually becomes its own dedicated lane of westbound Highway 40, so it was unclear what purpose an extended solid line would have there. But I'm no traffic engineer. So I asked Linda Wilson of MoDOT, and here is what she told us:

"The westbound I-64 ramp from Vandeventer is a long ramp that provides the distance for drivers to get up to speed. It is also important to note that the speed limit on this stretch of I-64 is 55 mph. The 60 mph limit starts just before Kingshighway. We will have the signing and striping looked at just make sure it doesn't need anything else."