YSK that if you are traveling westbound on even numbered highways or southbound on odd numbered highways, the exit numbers usually match with the miles left to the next state border.
from /r/YouShouldKnow
YSK认为，如果你在偶数公路上向西行驶或在奇数公路上向南行驶，出口号码通常与到下一个州边界的剩余里程相匹配。