You came to this page? Congratulations! You're a road geek (or you're lost, one of the two).

Here is a little expansion about sequential intersections:

The US highway and then the interstate system were both designed to follow a pattern: For US highways, even numbers were east-west roads increasing from north to south, and odd numbers were north-south roads increasing from east to west. The interstate system flopped the way the numbers increased: Even numbers were east-west roads increasing from south to north, and odd numbers were north-south roads increasing from west to east.

With this pattern, a diagonal line can be found where the odd meets the even and the two numbers are sequential. The US highway line, working northeast to southwest, starts in Houlton, Maine, with US 1 and 2, and ends at Fort Worth, Texas, where US 80 and 81 intersected once upon a time. (The diagonal US 84 created two exceptions beyond this: 83 and 84 intersect in Abilene, Texas, and 84 and 85 used to intersect in Santa Fe, New Mexico.) Somewhere along that approximated line are 19 and 20 in Erie, Pennsylvania; 30 and 31 in (near) Plymouth, Indiana; 40 and 41 in Terre Haute, Indiana; 50 and 51 in Sandoval, Illinois; 60 and 61 (and diagonal 62) near Sikeston, Missouri; and 70 and 71 in De Queen, Arkansas. Suprisingly, even with the wide variety and direction of three-digit US highways, three sequential intersections occur: US 201 and 202 in Augusta, Maine; 219 and 220 in Roanoke, Virginia; and 270 and 271 in Wister, Oklahoma.

Using the interstates, another diagonal line working northwest to southeast connects sequential intersections where one road is an interstate and the other a US highway. Iowa has two of them (I-29 and US 30; I-35 and US 34). Other sequential intersections like this are I-90 and US 89 in Bozeman, Montana; I-80 and US 81 near York, Nebraska; I-70 and both US 69 and US 71 in Kansas City (Kansas and Missouri, respectively); I-40 and US 41 in Nashville, Tennessee; and I-20 and US 21 in Columbia, South Carolina. US 11 intersects I-10 and I-12 in eastern Lousiana, but at this location 11 is violating numbering rules (like 84 above).