Characters can ride chariots in much the same way as large monsters. When shooting at a chariot, the hits are randomised between the character riding the chariot and the chariot itself. Roll a D6: on a roll of 6 the attack hits the character. Work out damage in the normal manner, except that the character either gains a +2 armour save bonus for riding the chariot or can use the armour save value of the chariot, whichever is the highest.
In close combat, enemies can choose whether to attack either the chariot or the character riding it.