If a person has a Class A license and wants to have the P endorsement added to their CDL would that person have to take a road test? Or could they just take the written test?

From fmsca website
http://www.fmcsa.dot.gov/

c) Endorsement testing requirements. The following tests are required for the endorsements contained in paragraph (b) of this section:

(c)(1) Double/Triple Trailers — a knowledge test;

(c)(2) Passenger — a knowledge and a skills test;

(c)(3) Tank vehicle - a knowledge test;

(c)(4) Hazardous Materials - a knowledge test; and

(c)(5) School bus - a knowledge and a skills test.

[67 FR 49760, Jul. 31, 2002; 68 FR 23850, May 5, 2003]