There should be no surprise that the completion of the South Lawrence Trafficway has had an impact on Kansas Turnpike Authority toll collections.

After all, one of the missions of the trafficway was to provide an alternative route between Topeka and the southern suburbs of Kansas City. Of course that’s going to peel some traffic off of I-70.

But it would be surprising if the trafficway, which stretches on Kansas Highway 10 for 15 miles east to west around Lawrence’s southern border, had a significant impact on KTA revenues, considering that the Lawrence exits account for a small percentage of total turnpike traffic.

KTA officials said last week that they’re monitoring traffic volume between Kansas City and Lawrence and its effect on toll revenue.

“We have noticed traffic changes, both increases and decreases at toll plazas in that area,” KTA spokeswoman Jeri Biehler said. “Any time there is a major traffic change, it takes three to four months for traffic to normalize. At this point in time, we are waiting to see what that traffic does and how things shift.”

According to KTA’s annual report, 79 million vehicles got on or off the turnpike in the fiscal year that ended June 30. About 15 percent — 12 million vehicles — got on or off one of the four exits between Exit 197 at Lecompton to the west and Exit 212 at Tonganoxie/Eudora to the east.

According to the KTA report, the busiest section of the turnpike, which stretches from the west edge of the Kansas City suburbs to Wichita, is the I-70 stretch between Kansas City and Topeka. Some 36 million vehicles got on or off the turnpike on this stretch in the past 12 months. Of those, 23 million entered or exited at the western edge in Topeka or the eastern edge in Kansas City. That means that a significant share of the traffic is simply passing through the 40-mile length of the turnpike on I-70. That traffic shouldn’t be altered by the presence of the South Lawrence Trafficway.

Another important point is that commercial vehicles pay significantly higher tolls — as much as three times higher — than passenger vehicles. Commercial vehicles accounted for only 11 percent of the vehicles on the turnpike but 34 percent of the toll revenue. The South Lawrence Trafficway isn’t expected to be highly used by commercial vehicles.

The South Lawrence Trafficway allows drivers to get from west Lawrence to Overland Park faster without paying a KTA toll. And a person driving from Topeka to Overland Park could also save miles and toll costs by getting off the Turnpike at Lecompton and taking the trafficway.

But outside of those travelers, the South Lawrence Trafficway should have minimal impact on KTA toll revenue, certainly less than the 8 percent the KTA grew toll revenues in the past 12 months.