Lowest number pair that doesn't meet?

[hotdogPi]

It was established in a previous thread that state level or higher 10 and 33 intersect nowhere in the US, but there is a county road junction.

What is the lowest number pair (positive integers only, and not the same number twice) in the US that doesn't exist in any form, where the pair is defined by its higher number? (For example, if we were doing state routes only, since we know 10 and 33 don't intersect, we would have to check all pairs where the higher number is 32 or lower, and 33 with 1-9).

US 2 and US 1

MA 3 and US 1
US 3 and US 2

RI 4 and US 1
MA 4 and MA 2
US 4 and US 3

I-5 and CA 1
US 5 and US 2
I-5 and CA 3
US 5 and US 4

US 6 and IL 1
US 6 and OH 2
US 6 and MA 3
...

[wanderer2575]

I was told there would be no math.

[ari-s-drives]

I don't believe that CA1 and CA2 ever meet.

[ClassicHasClass]

I don't believe that CA1 and CA2 ever meet.

They don't now, officially, but they used to until 1998 or thereabouts. https://www.cahighways.org/ROUTE002.html

[Scott5114]

Back in the day, there was a 10/33 junction in eastern Oklahoma. But US-412 took over that section of OK-33.

[SkyPesos]

In Ohio, US 33 used to intersect OH 10 in Lancaster, before the latter became part of a US 22 extension from Cambridge to Cincinnati and a new OH 10 was established near Cleveland.

[NWI_Irish96]

US 2 and US 1

MA 3 and US 1
US 3 and US 2

RI 4 and US 1
MA 4 and MA 2
US 4 and US 3

I-5 and CA 1
US 5 and US 2
I-5 and CA 3
US 5 and US 4

US 6 and IL 1
US 6 and OH 2
US 6 and MA 3

US 6 and OH 4
US 6 and IN 5

US 7 and US 1
US 7 and US 2
IN 7 and IN 3
US 7 and US 4
OH 7 and OH 5
IL 7 and US 6

IN 8 and IN 1
IN 8 and IN 2
IN 8 and IN 3
AK 8 and AK 4
I-8 and I-5
OH 8 and US 6
I-8 and CA 7

[TravelingBethelite]

It was established in a previous thread that state level or higher 10 and 33 intersect nowhere in the US, but there is a county road junction.

What is the lowest number pair (positive integers only, and not the same number twice) in the US that doesn't exist in any form, where the pair is defined by its higher number? (For example, if we were doing state routes only, since we know 10 and 33 don't intersect, we would have to check all pairs where the higher number is 32 or lower, and 33 with 1-9).

US 2 and US 1

MA 3 and US 1
US 3 and US 2

RI 4 and US 1
MA 4 and MA 2
US 4 and US 3

I-5 and CA 1
US 5 and US 2
I-5 and CA 3
US 5 and US 4

US 6 and IL 1
US 6 and OH 2
US 6 and MA 3
...

US 1 and CT 2 intersect just short of the state line in Stonington, if I'm not misunderstanding the prompt.