Why is DE 1 not an interstate?

[ixnay]

I get a kick out of the traffic reporters on WDEL referring to Exit 156 as "the jughandle".

[abqtraveler]

Regardless of whether or not DE 1 becomes an Interstate (hint: it won't), DE 1's exits should be converted from kilometer-based to mile-based. I understand why Interstate 19 has kilometer-based exit numbers, but DE 1 should never have had them, especially the exits south of DE 9.

It was because the DE-1 toll road was built in the early to mid-90s when there was a push for the US to convert to the metric system. I-19 in Arizona was built much earlier, but was signed in kilometers due to its proximity to the Mexican border. There are a lot of highways near the Canadian border that have dual mile/kilometer signage for the same reason.