The interline spacing between capitalized or uppercase words should be approximately three-fourths (¾) the average capital or uppercase letter height in adjacent lines of text (Figure 4‑17). For message text that includes a mileage numeral, the interline spacing should be determined with the numeral height and spaced between the common line of text (Figure 4‑17). In no case may the interline spacing be less that one-half (½) the average.

The interline spacing between a Route sign and the line of copy below should be equal to three-fourths (¾) the average height of the numeral in the Route sign and the largest letter, numeral, or arrow in the line of copy (Figure 4‑18). The interline spacing should then be between the lowest point on the Route sign and the top of the line of text.

The interline spacing between a line of text and an upward sloping arrow should be equal to three-fourths (¾) the height of the uppercase letters in the line above the arrow (Figure 4‑19).

The interline spacing between a Route sign and an upward sloping arrow should be equal to three-fourths (¾) the height of the numerals inside the Route sign (Figure 4‑20).