The use of carts at golf courses seems to be increasing, in spite of the fact that the USGA and many state golf associations encourage walking. However, many courses have been designed where the player absolutely has no choice but to take a cart or forfeit play of the course. For that reason, in addition to preference, there are situations you should be aware of when carts enter the equation; and these are a few examples:

A cart runs over your ball in play, embedding it into the turf.

• If this cart belongs to the rules official, you must replace the ball per Rule 18-1 [Ball at Rest Moved By Outside Agency]. There is no penalty, but the original lie has been altered; and Rule 20-3b applies, which states: "If the original lie of a ball to be placed or replaced has been altered: except in a hazard, the ball shall be placed in the nearest lie most similar to the original lie which is not more than one club-length from the original lie, not nearer the hole and not in a hazard………"
  
  
• If this cart belongs to you or your partner (whether it is shared by you or not), Rule 20-3b applies as stated above. HOWEVER, you will be penalized one stroke in stroke play or in match play under Rule 18-2 [Ball at Rest Moved by Player, Partner, Caddie, or Equipment].
  
  
• If this cart belongs to your opponent (match play) during the search for the ball, or your fellow-competitor [stroke play] at any time, there is no penalty; and Rule 20-3b applies as stated above.
  
  
• If this cart belongs to your opponent, and other than during search for the ball, Rule 20-3b applies as stated above; and the opponent shall incur a penalty of one stroke per Rule 18-3.

You have just hit a fabulous drive and as it is coming to earth for its first of many bounces:

• A cart from a neighboring hole roars into its path, deflecting it backwards twenty-five yards. You must play this ball as it lies under Rule 19-1 [Ball in Motion Deflected or Stopped by Outside Agency].
  
  
• It glances off of the edge of the paved cart path bisecting the fairway. The ball kicks hard right and out of bounds. You must proceed under Rule 27-1 [Ball Lost or Out of Bounds] and re-tee, hitting three.

from Ladies Golf Journey - Jul/Aug 2003