An picture of a section of freeway with route shield markings painted within the lanes.  The left two lanes have an <a href="//commons.wikimedia.org/wiki/Category:Interstate_30_in_Texas" title="Category:Interstate 30 in Texas">I-30</a> shield, and the right two lanes have an <a href="//commons.wikimedia.org/wiki/Category:Interstate_35E_(Texas)" title="Category:Interstate 35E (Texas)">I-35E</a> shield.
Federal Highway Administration
<a rel="nofollow" class="external text" href="https://safety.fhwa.dot.gov/older_users/fhwasa15088/ch3.cfm#fig50">Handbook for Designing Roadways for the Aging Population</a> <a rel="nofollow" class="external autonumber" href="https://safety.fhwa.dot.gov/older_users/fhwasa15088/images/fig_50.png">[1]</a>