Advance Approach

I may not be a master in signals nor understand much about them but I know one thing though it's how railroads display Advance Approach.  *Y*/R , Y/G & Y/Y while each one state's an Advance Approach the description is different for each Railroad.

 ^ ADVANCE APPROACH in all forms.

*Y* Ex-Conrail Territory & Y/Y Ex- Southern & Norfolk &Western Territory

^ ADVANCE CLEAR to STOP in Canada form.

*Y*, *Y*/R, *Y*/R/R UNION PACIFIC : ADVANCE APPROACH  

Proceed prepared to stop at second signal.  Freight trains exceeding 40 MPH must immediately reduce to 40 MPH.  Passenger trains may proceed, but must be prepared to pass the next signal not exceeding 40 MPH.  When signal governs the approach to a control point with a 40 MPH turnout speed be prepared to advance on normal or diverging route. *

*Y*, *Y*/R, *Y*/R/R NORFOLK SOUTHERN's Ex-CONRAIL Lines ADVANCE APPROACH

Proceed prepared to stop at the second signal. Trains exceeding Limited speed must begin reduction to Limited speed as soon as engine passes the Advance Approach signal.

*Y*, *Y*/R, *Y*/R/R CSX's Ex-CONRAIL Lines : ADVANCED APPROACH

Proceed, prepared to stop at the second signal. Trains exceeding Limited speed must begin reduction to Limited speed as soon as locomotive passes the Advance Approach signal

*Y*, *Y*/R, *Y*/R/R CN & CP (Canada Lines) : Advance Clear to Stop : Proceed, prepared to Stop at second signal.

Y/G BNSF :

ADVANCED APPROACH Proceed prepared to pass next signal not exceeding

50 MPH and be prepared to enter diverging route at prescribed speed.

Y/Y CSX : ADVANCE APPROACH

Proceed, prepared to stop at second signal.

Y/Y NORFOLK SOUTHERN :

ADVANCE APPROACH
Proceed preparing to stop at second signal.

Y/Y Norfolk Southern Ex-NW :

ADVANCE APPROACH 

Proceed preparing to stop at second signal.

(* When the next signal is seen to display an aspect more favorable than APPROACH or DIVERGING APPROACH, the requirement to proceed prepared to stop short of the second signal is no longer required.)

(credit to Misterpsychopath3001 for the signal base.)