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The number 100,000 is big.

West Jordan, the state's fourth-largest city, has about that many residents. That number of people would fill EnergySolutions arena five times.

It's also about how many cars pass through the intersection of 5400 South and Redwood Road on an average day — 99,915 to be exact.

That makes it the state's busiest surface-street intersection (freewaylike interchanges are not counted), according to Utah Department of Transportation data.

"I'm not at all surprised," said Taylorsville resident Elaine Cook as she loaded groceries into her car at an adjacent Harmons grocery store and prepared to battle through that intersection again. Some students at nearby Taylorsville High walk or drive through it twice a day.

Redwood Road has eight of the state's 50 busiest intersections. Bangerter Highway has 12. Salt Lake County's State Street has eight, and Utah County's State Street six. University Avenue in Utah County has five.

Busiest intersection • UDOT has improvements planned soon for many of those busiest intersections, but not at 5400 South and Redwood.

UDOT Deputy Director Shane Marshall said an improvement was made there in 2010 that should handle its traffic for another 15 to 20 years. UDOT calls it a continuous-flow intersection (CFI) design.

Cook, as she loaded her groceries, called it "that stupid thing."

The CFI design saves a little time by eliminating left-turn signals off 5400 South. Those wanting to turn left must queue up well in advance of the intersection. A signal then allows them to cross oncoming traffic into a special lane on the extreme left of the road — and turn left while other traffic on 5400 South proceeds straight.

Cook said she uses "that stupid thing" to turn onto Redwood and then immediately turn into Harmons. But "people turning right off 5400 South make it tough, and it's a little crazy there" with the merging traffic.

Adding to the general confusion around that intersection is that just to the west of it is where the state's only "flex lanes" begin — where some 5400 South lanes change direction during the day. Four lanes go with the heaviest drive-time flow, while two go in the direction of lighter traffic.

Marshall conceded that CFIs are unusual and can be confusing — but said most Utahns are accustomed to them after many have been installed.

"For a relatively small amount of money, you can get a big bang and it will last quite a long time" to improve flow, he said, adding that a CFI is five times cheaper than building a freewaylike grade-separated interchange.

Marshall said such a freewaylike interchange at 5400 South and Redwood "would be very difficult. The access to many businesses is literally 100 feet away from that intersection."

Second busiest • But UDOT is looking at possibly installing such a freewaylike interchange at the state's second-busiest intersection: University Parkway and State Street near the University Mall in Orem.

He said when UDOT worked with the Utah Transit Authority on plans for a "bus rapid transit" system along University Parkway — which has a dedicated lane for buses — it examined many options to improve that intersection.

"We really couldn't find a solution that lasted into 2040," he said. So the Utah Transportation Commission last month approved a $1.5 million study about possibly converting it into a freewaylike intersection, with one road passing over the other and ramps connecting them.

"The difficult part there is the access to the mall and some other businesses that are really close to that intersection," Marshall said. "How do you balance that access with moving people?"

Busy Bangerter • Bangerter Highway in western Salt Lake County has six of the 10 busiest intersections in the state, and 12 of the top 50. Many already are CFIs, but UDOT is considering converting them into freewaylike interchanges over time.

Earlier this month, it completed one such conversion at Bangerter and Redwood Road — which was the 16th busiest in the state with 71,805 vehicles on an average day. UDOT earlier completed another conversion at Bangerter and 7800 South.

Many of the Bangerter intersections scheduled for conversion in the near future are not necessarily the busiest ones. The next conversion scheduled — at 600 West — isn't even among the top 50 busiest intersections. But it is near the new conversion at Redwood, and Marshall said the combination of the two will help overall traffic flow near Interstate 15.

The four others scheduled and funded for conversion between 2017 and 2022 areat 11400 South (15th busiest, 71,845 cars daily), 9000 South (ninth, 81,105), 7000 South (13th, 73,890 cars) and 5400 South (third busiest, 93,860 cars).

Marshall said UDOT generally is trying to work south to north on Bangerter, and that most of the intersections have about the same amount of traffic.

He said some Bangerter intersections not yet firmly scheduled for freewaylike conversions "will be next on the list" in long-range plans.

Some of them include Bangerter intersections at 3500 South (ranked fourth among busiest intersections, 87,785 cars daily), 4700 South (fifth, 85,385 cars), 6200 South (eighth, 83,955 cars) and 4100 South (10th, 79,360 cars).

At the dedication of the new interchange on Bangerter at Redwood Road, Riverton Mayor Bill Applegarth praised UDOT's approach to upgrading intersections only as needed by traffic.

He said that had UDOT built Bangerter as a freeway from the outset, it would "use up precious funds that cannot be used in other projects."

Elsewhere • Improvements are planned for some, but not all, of the other busiest roads around the state.

The intersection of Bluff Street and Sunset Boulevard in St. George is No. 6 on the list with 85,340 cars a day. It had been under consideration for conversion into a freewaylike interchange, but instead will receive some improvements, including putting a pedestrian undercrossing there.

"Taking the pedestrians out of that intersection," Marshall said, "allowed us to meet traffic demand to 2030."

Among the busiest intersections where no improvements are on the horizon are: Redwood Road and 6200 South in Taylorsville (ranked seventh, 84,110 cars a day); State Street and 800 North in Orem (11th, 78,515 cars); Redwood and 9000 South in West Jordan (12th, 74,695 cars) and Redwood and 4700 South in Taylorsville (14th, 73,700 cars).

Average daily car volume at Utah's busiest intersections

1. Redwood Road and 5400 South, Taylorsville • 99,915

2. State Street at University Parkway, Orem • 97,190

3. Bangerter Highway at 5400 South, Taylorsville • 93,860

4. Bangerter at 3500 South, West Valley City • 87,785

5. Bangerter at 4700 South, West Valley City • 85,385

6. Bluff Street at Sunset Boulevard, St. George • 85,340

7. Redwood Road at 6200 South, Taylorsville • 84,110

8. Bangerter at 6200 South, Taylorsville • 83,955

9. Bangerter at 9000 South, West Jordan • 81,015

10. Bangerter at 4100 South, West Valley City • 79,360

Source: Utah Department of Transportation